Table 2 – Indices acc accumulator gen generation subsystem on on aux auxiliary gnr generator op operation avg average grs gross out output from subsystem brm boiler room H heating P0 at
Terms and definitions
For the purposes of this document, the terms and definitions given in EN ISO 7345:1995 and the following apply
3.1.1 space heating process of heat supply for thermal comfort
3.1.2 domestic hot water heating process of heat supply to raise the temperature of the cold water to the intended delivery temperature
3.1.3 heated space room or enclosure which for the purposes of the calculation is assumed to be heated to a given set-point temperature or set-point temperatures
System thermal loss refers to the heat energy that escapes from a technical building system, such as those used for heating, cooling, domestic hot water, humidification, dehumidification, ventilation, or lighting This loss does not contribute to the system's useful output, highlighting the importance of minimizing thermal losses to enhance energy efficiency.
NOTE Thermal energy recovered directly in the subsystem is not considered as a system thermal loss but as heat recovery and is directly treated in the related system standard
3.1.5 auxiliary energy electrical energy used by technical building systems for heating, cooling, ventilation and/or domestic hot water to support energy transformation to satisfy energy needs
The electrical energy used for fans, pumps, and electronics in a ventilation system is essential for air transport and heat recovery This energy is classified as energy use for ventilation rather than auxiliary energy.
Heat recovery refers to the process of capturing heat generated by a technical building system or associated with building usage, such as domestic hot water This recovered heat is then utilized directly within the related system to reduce the required heat input, preventing waste An example of this is the preheating of combustion air using a flue gas heat exchanger.
3.1.7 total system thermal loss total of the technical system thermal loss, including recoverable system thermal losses
Recoverable system thermal loss refers to the portion of thermal energy loss within a system that can be reclaimed This recovery process helps to reduce the energy required for heating or cooling, as well as the overall energy consumption of the heating or cooling systems.
The recovered system thermal loss contributes to reducing the energy required for heating or cooling, as well as minimizing the energy consumption of the heating or cooling systems.
The gross calorific value refers to the total amount of heat released from a unit of fuel when it is completely combusted with oxygen at a constant pressure of 101,320 Pa, with the combustion products subsequently returned to ambient temperature.
This quantity accounts for the latent heat of condensation from both the water vapor present in the fuel and the water vapor produced by the combustion of hydrogen within the fuel.
NOTE 2 According to ISO 13602-2, the gross calorific value is preferred to the net calorific value
NOTE 3 The net calorific value does not take into account the latent heat of condensation
3.1.11 net calorific value gross calorific value minus latent heat of condensation of the water vapour in the products of combustion at ambient temperature
3.1.12 calculation step discrete time interval for the calculation of the energy needs and uses for heating, cooling, humidification and dehumidification
NOTE Typical discrete time intervals are one hour, one day, one month or one heating and/or cooling season, operating modes, and bins
3.1.13 calculation period period of time over which the calculation is performed
NOTE The calculation period can be divided into a number of calculation steps
3.1.14 external temperature temperature of external air
For transmission heat transfer calculations, it is assumed that the radiant temperature of the external environment matches the external air temperature, while long-wave transmission to the sky is calculated independently.
NOTE 2 The measurement of external air temperature is defined in EN ISO 15927-1
A boiler is an appliance that uses gas, liquid, or solid fuel to generate hot water for space heating While its primary function is to provide heating, it may also be designed to supply domestic hot water.
3.1.16 combustion power product of the fuel flow rate and the net calorific power of the fuel
A condensing boiler is engineered to utilize the latent heat generated from the condensation of water vapor in the combustion flue gases It is essential for the boiler to facilitate the exit of condensate in liquid form through a designated condensate drain from the heat exchanger.
NOTE Boilers not so designed, or without the means to remove the condensate in liquid form, are called ‘non- condensing’
3.1.18 modes of operation various modes in which the heating system can operate (set-point mode, cut-off mode, reduced mode, set- back mode, boost mode)
3.1.19 modulating boiler boiler with the capability to vary continuously (from a set minimum to a set maximum) the fuel burning rate whilst maintaining continuous burner firing
The accumulator storage system is a crucial component of the generation system, designed to store excess heat generated during operation This excess heat arises from the disparity between the boiler's output and the actual heat input to the heating system.
A load balancing storage system is a crucial component of the generation system tank that enhances operational conditions during runtime This improvement leads to reduced starting intervals and extended running time for automatically fired biomass boilers, as outlined in EN 15316-4-1.
3.1.22 biomass boiler biomass fuelled appliance designed to provide heating medium (e.g water, fluid) for space heating
3.1.23 load factor ratio between the time with the boiler ON and the total generator operation time
3.1.24 operation cycle time period of the operation cycle of a boiler
Symbols and units
For the purposes of this document, the following symbols and units (Table 1) and indices (Table 2) apply
Symbol Name of quantity Unit b temperature reduction factor c - c coefficient c various c specific heat capacity J/kgãK or
E energy in general (except quantity of heat, mechanical work and auxiliary (electrical) energy
H calorific value J/mass unit or
H heat transfer coefficient c W/K k factor c - m mass kg n exponent -
P power in general including electrical power W
Wh a t time, period of time s or h a
W auxiliary (electrical) energy, mechanical work J or
Wh a α loss factor % β load factor -
∆ prefix for difference η efficiency factor % θ Celsius temperature °C Φ heat flow rate, thermal power W a If seconds (s) is used as the unit of time, the unit for energy needs to be J;
When measuring energy in watt-hours (Wh), time is expressed in hours (h) The mass of fuel can be represented in various units such as standard cubic meters (Stm³), normal cubic meters (Nm³), or kilograms (kg) It's important to note that coefficients have dimensions, while factors are dimensionless.
Heat balance of the biomass combustion sub-system, including control of heat
Physical factors for biomass combustion sub-system ( biomass boiler ) taken into
The calculation method of the boiler takes into account heat losses and/or recovery due to the following physical factors:
heat losses to the chimney (or flue gas exhaust) during total time of boiler operation (running and stand-by);
heat losses through the boiler envelope during total time of boiler operation (running and stand-by);
The relevance of these effects on the energy requirements depends on:
operating conditions (temperature, control etc.);
control strategy (on/off, modulating).
Calculation structure (input and output data)
The calculation method of this European Standard shall be based on the following:
heat demand of the distribution sub-system(s) for space heating, ΣQ H,dis,in, calculated according to
heat demand of the distribution sub-system(s) for domestic hot water, ΣQ W,dis,in, calculated according to
The performance of the boiler may be characterised by additional input data to take into account:
type and characteristics of the boiler;
type of the boiler control system;
Based on these data, the following output data are determined by calculations according to this European Standard:
fuel heat requirement, E H,gen,in;
total generation thermal losses (flue gas and boiler envelope), Q H,gen,ls;
recoverable generation thermal losses, Q H,gen,ls,rbl;
generation auxiliary energy, W H,gen,aux
Figure 1 shows the calculation inputs and outputs of the generation sub-system
SUB generation sub-system balance boundary
HF heating fluid balance boundary (see Equation (1))
Q H,gen,out generation sub-system heat output (input to distribution subsystem(s))
E H,gen,in generation sub-system fuel input (energyware)
W H,gen,aux generation sub-system total auxiliary energy
Q H,gen,aux,rvd generation sub-system recovered auxiliary energy
Q H,gen,ls generation sub-system total thermal losses
Q H,gen,ls,rbl generation sub-system thermal losses recoverable for space heating
Q H,gen,rbl,th generation sub-system thermal loss (thermal part) recoverable for space heating
Q H,gen,rbl,aux generation sub-system recoverable auxiliary energy
Q H,gen,nrbl,th generation sub-system thermal loss (thermal part) non recoverable
Q H,gen,nrbl,aux generation sub-system non recoverable auxiliary energy
NOTE Figures shown are sample percentages
Figure 1 — General generation sub-system inputs, outputs and energy balance
Generation sub-system basic energy balance
The basic energy balance of the generation sub-system is given by: ls H,gen, rvd aux, H,gen, H,gen,out in
E H,gen,in heat requirement of the generation sub-system (fuel input);
Q H,gen,out heat supplied to the distribution sub-systems (space heating);
Q H,gen,aux,rvd auxiliary energy recovered by the generation sub-system (e.g pumps, burner fan);
Q H,gen,ls total thermal losses of the generation sub-system (e.g through the chimney, generator envelope)
NOTE 1 Q H,gen,ls takes into account flue gas and boiler envelope losses, part of which may be recoverable for space heating according to location of the boiler See A.4.2
If the boiler supplies heat for both space heating and domestic hot water, the index H should be substituted with HW For simplicity, H will be used in the following sections, except in Equation 2.
NOTE 3 Generally biomass boilers are not designed for controlling the emission part of heating systems
If there is only one boiler, the heat output from the boiler equals the sum of heat input to the connected distribution systems:
= i H, dis, in, i j W, dis, in, j out gen,
Auxiliary energy
Auxiliary energy refers to the energy needed for the operation of the burner, primary pump, and related equipment in the heat generation sub-system, excluding fuel This energy is included in the generation phase as long as it does not transfer transport energy to the distribution sub-system, such as in a zero-pressure distribution array While auxiliary equipment may be part of the boiler, it is not a requirement.
Auxiliary energy, normally in the form of electrical energy, may partially be recovered as heat for space heating or for the generation sub-system
Examples of recoverable auxiliary energy:
electrical energy transmitted as heat to the water of the primary circuit;
part of the electrical energy for the boiler fan
Example of non-recoverable auxiliary energy:
electrical energy for electric panel auxiliary circuits, if the boiler is installed outside the heated space.
Recoverable, recovered and unrecoverable system thermal losses
Not all of the calculated system thermal losses are necessarily lost Some of the losses are recoverable and part of the recoverable system thermal losses are actually recovered
Example of recoverable system thermal losses:
thermal losses through the envelope of a boiler installed within the heated space
Examples of non-recoverable system thermal losses:
thermal losses through the envelope of a boiler installed outside the heated space;
thermal losses (flue gas losses) through the chimney
Recovery of system thermal losses to the heated space can be accounted for:
either as a reduction of total system thermal losses within the specific part (simplified method);
or by taking into account recoverable system thermal losses as gains (holistic method) or as a reduction of the energy use according to EN 15603
This European Standard allows both approaches
Generation system thermal losses recovered by the generation sub-system are directly taken into account in the generation performance
EXAMPLE Combustion air preheating by flue gas losses.
Calculation steps
The goal of this calculation is to assess the energy input of the heating generation sub-system and the overall system losses over a typical one-year period This can be achieved through one of two distinct methods.
by using average data for the entire calculation period and performing the calculations using average values (usually annual data and values);
To calculate energy performance, divide the calculation period into several steps, such as months or weeks, as specified in EN ISO 13790 Perform calculations for each step using values that depend on the specific step, and then sum the results across all steps for the entire calculation period.
For biomass boilers with stocking by hand, the calculation period shall be 24 h.
Using net or gross calorific values
Calculations described in Clause 7 may be performed according to net or gross calorific values All parameters and data shall be consistent with this option
If the calculation of the boiler energy performance is performed according to data based on net calorific values
Total losses, including net non-recoverable thermal losses and energy input for combustion systems, can be converted from net to gross calorific values This conversion involves adding the latent heat of condensation to the respective values, ensuring accurate representation of energy metrics in thermal systems.
Q = ⋅ − (3) lat net in, gen, H, grs in, gen,
E = + (4) lat net ls, gen, H, grs ls, gen,
Q = + (5) lat net nrbl, th, ls, gen, H, grs nrbl, th, ls, gen,
The latent heat of condensation, denoted as \$Q_{lat}\$, significantly varies based on factors such as the type of biomass fuel, its origin, and storage quality Consequently, it is essential to provide reference values in a national annex.
Boundaries between distribution and generation sub-system
Boundaries between generation sub-system and distribution sub-system should be defined according to the principles described in 4.8 of EN 15316-4-1:2005
5 Biomass combustion sub-system calculation
The performance calculation methods for biomass combustion systems differ with respect to:
type of stocking device (automatic or by hand);
type of biomass fuel (pellets, chipped wood or log wood)
6 Calculation method for boilers with automatic stocking
The performance calculation methods for biomass boilers with automatic stocking are similar to those used for automatically fired boilers that utilize oil or gas These methods are detailed in the EN 15316-4-1 standard.
NOTE 1 Biomass boilers with automatic stocking fired by pellets or chipped wood
To enhance efficiency and minimize pollution, it is advisable to utilize biomass boilers equipped with an automatic stocking system that incorporates load balancing storage For further information on calculating load balancing storage systems, please refer to Annex C.
7 Calculation method for boilers with stocking by hand
Available methodologies
In this European Standard, two performance calculation methods for biomass boilers with stocking by hand are described The calculation methods differ with respect to:
operating conditions (operation cycles) taken into account;
The initial approach, outlined in section 7.3 regarding the case-specific boiler efficiency method, relies on data from test procedures in accordance with EN 303-5 However, additional information is required to consider the unique operational conditions during the heating season.
The second method, known as the boiler cycling method, explicitly identifies the combustion losses that occur during boiler cycling Certain parameters can be measured directly on-site to enhance accuracy.
NOTE 1 Biomass boilers with stocking by hand fired by logwood
According to EN 303-5, it is advisable to operate biomass boilers using manual stocking in conjunction with an accumulator storage system For further information on calculating accumulator storage systems, refer to Annex C or the EN 303-5 standard.
Operation periods
General
The operation periods for biomass boilers with stocking by hand are divided into two main periods according to the different types of operation cycles as follows:
boiler in operation t gnr,on consisting of 3 sub-periods:
- boiler heating up t gnr,hup
- boiler heating operation t gnr,op
- boiler cooling down t gnr,cod
boiler in non operation t gnr,off consisting of 2 sub-periods:
- boiler in fire bed operation t gnr,fib
- boiler in non operation t gnr,non
The total operation period t gnr,tot of the boiler is given by: t gnr,tot = t gnr,on + t gnr,off (7)
NOTE Boiler in fire bed operation is only relevant for boilers with fan assistance.
Heating up operation cycle
The operation period for the heating up operation cycle t gnr,hup is influenced by:
quality of the biomass fuel applied;
quantity of the biomass fuel applied (according to the required quantity of the loaded biomass fuel).
Boiler heating operation cycle
The operation period for the heating operation cycle t gnr,op is influenced by:
quality of the biomass fuel applied;
quantity of the biomass fuel applied (according to the required quantity of the loaded biomass fuel);
intermediate load of the boiler
The running time of the boiler in heating operation cycle, t gnr,op,d is calculated by: d avg out gnr H d in dis
, = Φ (h) (8) where t gnr,op,,d running time in heating operation cycle within a 24 h operation period in h;
The total heat required for the distribution system over a 24-hour operation period is denoted as \$Q_{H,dis,in,d}\$ in kWh Meanwhile, the average heat output from the biomass boiler during the same 24-hour period is represented as \$\Phi_{H,gnr,out,avg,d}\$ in kW.
Cooling down operation cycle
The operation period for the cooling down operation cycle t gnr,cod is influenced by:
time when the operation cycle starts again;
mass of the relevant parts of the boiler;
water content of the boiler;
heat loss of the envelope
NOTE By a permanent operation cycle it is assumed, that the next heating up operation cycle starts immediately after the end of the cooling down operation cycle.
Boiler non operation cycle
Depending on the heat to be supplied to the distribution system during a 24 h operation period, two different types of non operation cycles are to be considered:
boiler in fire bed operation cycle - operation period t gnr,fib
NOTE 1 In this case, the boiler temperature is the same as the regular boiler operating temperature
boiler in non operation cycle - operation period t gnr,non
NOTE 2 In this case, the boiler temperature is the same as the ambience temperature (no heat loss).
Case specific boiler efficiency method
Principle of the method
This method pertains to test values in accordance with relevant European Standards In the absence of available values, default values are provided in Annex A or a national annex Data is gathered for three fundamental load factors or power outputs.
η gnr,Pn efficiency at 100 % load;
η gnr,Pint efficiency at intermediate load;
At 0% load, the heat losses, denoted as Ф gnr,ls,P0, are assessed, while efficiencies and heat loss data are adjusted based on the actual operating temperature of the boiler Thermal losses at full load (Ф gnr,ls,Pn) and at intermediate load (Ф gnr,ls,Pint) are computed using these temperature-corrected efficiencies Additionally, the calculation of thermal losses for the actual power output is performed through linear or polynomial interpolation between the thermal losses identified for three primary power outputs.
In the case-specific boiler efficiency method, thermal losses and the load factor β gnr are based on boiler output Auxiliary energy is determined by the actual power output of the boiler Recoverable boiler envelope thermal losses are calculated using a tabulated fraction of standby heat losses and the boiler's location The total recoverable thermal losses are obtained by adding recoverable auxiliary energy to the recoverable boiler envelope thermal losses.
Input data to the method
The boiler is characterised by the following data:
Ф Pn boiler output at full load;
η gnr,Pn boiler efficiency at full load;
θ gnr,w,test,Pn boiler average water temperature at test conditions for full load;
f corr,Pn correction factor for full-load efficiency;
Ф Pint boiler output at intermediate load;
η gnr,Pint boiler efficiency at intermediate load;
θ gnr,w,test,Pint boiler average water temperature at test conditions for intermediate load;
f corr,Pint correction factor for intermediate load efficiency;
Ф gnr,ls,P0 stand-by heat loss at test temperature difference ∆θ gnr,test,P0;
∆θgnr,test,P0 difference between mean boiler temperature and test room temperature at test conditions;
P aux,gnr,Pn power consumption of auxiliary devices at full load;
P aux,gnr,Pint power consumption of auxiliary devices at intermediate load;
P aux,gnr,P0 stand-by power consumption of auxiliary devices;
θ gnr,w,min minimum operating boiler temperature
To accurately characterize a boiler, data should be sourced in the following order of priority: first, utilize product data from the manufacturer if the boiler has been tested in accordance with EN 303-5; second, refer to the default data provided in the relevant national annex.
If no data according to a) or b) are available, default data are given in Annex A
It shall be recorded whether or not the efficiency values include auxiliary energy recovery
Actual operating conditions are characterised by the following data:
Q H,gnr,out heat output to the heat distribution sub-system(s);
θgnr,w,m average water temperature in the boiler;
b brm temperature reduction factor depending on the location of the boiler.
Load of the boiler
Boiler average power Ф H,gnr,out is given by: tot gnr out gnr
, = Φ (9) where t gnr,tot is the total time of boiler operation
The load ratio factor β gnr during the heating operation cycle is given by:
= Φ , , β (10) where Ф Pn is the nominal power output of the boiler (kW); Φ H,gnr,out is the average boiler output (kW)
The average boiler output is calculated by:
The heat output for each filling of the combustion chamber, denoted as \$\Phi_{gnr,cham}\$, is measured in kW When evaluating boiler performance, it is essential to refer to the relevant EN 303-5 standards In cases where specific values are unavailable, default values should be utilized as outlined in the applicable national annex The reference combustion power is represented as \$\Phi_{gnr,cham,ref}\$ in kW.
7.3.3.3 Boiler with double service (space heating and domestic hot water production)
During the heating season, a biomass boiler efficiently provides energy for both space heating and domestic hot water Unlike other systems, it does not require a specific calculation for the operating temperature.
NOTE The minimum operating temperature of biomass boilers are always higher than the required running temperature of the domestic hot water production.
Biomass boiler thermal losses
7.3.4.1 Biomass boiler thermal loss calculation at full load
The full load efficiency, denoted as \$\eta_{gnr,Pn}\$, is evaluated at a reference average water temperature of the biomass boiler, \$\theta_{gnr,w,test,Pn}\$ This efficiency must be modified to reflect the actual average water temperature of the specific installation.
The temperature corrected efficiency at full load η gnr,Pn,corr is calculated by:
The boiler efficiency at full load, denoted as \$\eta_{gnr,Pn}\$, is determined using the equation \$\eta_{gnr,Pn} = Pn_{corr} + Pn_{gnr} \cdot w_{test} - Pn_{gnr} \cdot w_{m}\$ (12) This performance assessment is conducted in accordance with relevant testing standards.
When evaluating boiler performance, European Standards should be considered, and if specific values are unavailable, default values provided in section A.2.1 or the relevant national annex should be used The correction factor, denoted as \$f_{corr,Pn}\$, accounts for variations in full load efficiency based on the boiler's average water temperature, which should also be specified in the national annex In cases where national values are lacking, the default values in A.2.1 apply Additionally, the average water temperature during testing, represented as \$\theta_{gnr,w,test,Pn}\$, is crucial for assessing full load conditions, while \$\theta_{gnr,w,m}\$ reflects the average water temperature under specific operating conditions.
To streamline calculations, the efficiencies and heat losses measured under test conditions are modified to reflect the actual average water temperature of the boiler This adjustment is valid, as it accurately aligns performance metrics with the average water temperature corresponding to each load.
The corrected biomass boiler thermal loss at full load Ф gnr,ls,Pn,corr is calculated by:
Pn gnr corr Pn gnr corr
( η η (13) where Ф Pn boiler output at full load
7.3.4.2 Biomass boiler thermal loss calculation at intermediate load
The efficiency at intermediate load, denoted as \$\eta_{gnr,Pint}\$, is evaluated at a reference boiler average water temperature, \$\theta_{gnr,w,test,Pint}\$ This efficiency must be modified to reflect the actual average water temperature of the specific installation.
The temperature corrected efficiency at intermediate load η gnr,Pint,corr is calculated by:
The equation for boiler efficiency at intermediate load is given by \$$\eta_{gnr,P} = \eta_{gnr} + f_{corr,P} \cdot (θ_{gnr,w,test,P} - θ_{gnr,w,m})\$$ where \$\eta_{gnr,P}\$ represents the efficiency of the boiler If the boiler's performance has been evaluated according to relevant European Standards, those results can be utilized In cases where no specific values are available, default values can be found in section A.2.1 or the applicable national annex The correction factor \$f_{corr,P}\$ accounts for variations in efficiency based on the average water temperature in the boiler, which should also be referenced in the national annex If national values are not provided, default values from A.2.1 should be used Additionally, \$θ_{gnr,w,test,P}\$ denotes the average water temperature during testing at intermediate load, while \$θ_{gnr,w,m}\$ indicates the average water temperature under specific operating conditions.
The intermediate load depends on the boiler type Default values are given in A.1
The corrected biomass boiler thermal loss at intermediate load Φgnr,ls,Pint,corr is calculated by: int int,
= Φ η η (15) where Ф Pint boiler output at intermediate load
7.3.4.3 Biomass boiler thermal loss calculation at 0 % load
The boiler heat loss at 0% load, denoted as Φ gnr,ls,P0, is calculated based on a specified test temperature difference in accordance with relevant tests In the absence of manufacturer or national annex data, default values are provided in section A.2.2.
The temperature corrected boiler thermal loss at 0 % load Φgnr,ls,P0,corr is calculated by:
P test gnr brm i m w gnr P ls gnr corr
The equation \( P_{\text{ls}} = g_{\text{nr}} \theta \) describes the heat loss at 0% load, considering the test temperature difference \( \Delta \theta_{\text{gnr,test}} \) and the average water temperature in the boiler, \( \theta_{\text{gnr,w,m}} \), which varies based on specific operating conditions.
7.3.8); θ i,brm indoor temperature of the boiler room Default values are given in A.4.3;
∆θ gnr,test,P0 difference between mean boiler temperature and test room temperature at test conditions
Default values are given in A.2.2
7.3.4.4 Boiler thermal loss at specific load ratio β gnr and power output Ф Px
The specific load ratio β gnr of the boiler is calculated according to 7.3.3
The actual power output Ф Px of the boiler is given by gnr Pn
If Ф Px is between 0 (β gnr = 0) and Ф Pint (intermediate load, β gnr = β int = Ф Pint/Ф Pn), the boiler thermal loss Φgnr,ls,Px is calculated by: corr P ls gnr corr
P ls gnr corr P ls gnr P
Px Px ls gnr , , int, , , 0 , , , 0 , int
If Ф Px is between Ф Pint and Ф Pn (full load, β gnr = 1), the boiler thermal loss Φgnr,ls,Px is calculated by: corr P ls gnr corr
P ls gnr corr Pn ls gnr P
Px Px ls gnr , , , , , int, , , int, int int ,
= Φ Φ (19) Φgnr,ls,Px may also be calculated by 2 nd order polynomial interpolation An equation for such interpolation is given in Annex B of EN 15316-4-1:2005
The total boiler thermal loss Q gnr,ls during the considered time of operation t gnr,tot of the biomass boiler is calculated by: tot gnr Px ls gnr ls gnr t
The total generation sub-system thermal losses are the sum of the boiler thermal losses:
Total auxiliary energy
The total auxiliary energy for a biomass boiler is given by:
( ci gnr, tot ) off aux, tot gnr, Px aux, aux gnr, P t P t t
P aux,Px auxiliary power consumption corresponding to the actual power output ΦPx of the boiler;
P aux,off auxiliary power consumption when the boiler is not operating; t ci calculation interval; t gnr,tot total time of boiler operation within the calculation interval
The average auxiliary power consumption for each boiler P aux,Px is calculated by linear interpolation, according to the boiler load β gnr, between:
P aux,Pn auxiliary power consumption of the boiler at full load (β gnr = 1);
P aux,Pint auxiliary power consumption of the boiler at intermediate load (β gnr = β int);
P aux,P0 auxiliary power consumption of the boiler at stand-by (β gnr = 0);
If 0 ≤ β gnr ≤ β int then P aux,Px is given by:
If β int < β gnr ≤ 1 then P aux,Px is given by:
, 1 aux Pn aux P gnr P aux Px aux P P P
The generation sub-system auxiliary energy W H,gen,aux is given by:
In the absence of detailed values, the power consumption of the auxiliary equipment can be calculated according to A.3.
Recoverable generation system thermal losses
For the recoverable auxiliary energy, a distinction is made between:
recoverable auxiliary energy transmitted to the heating medium (e.g water) It is assumed, that the auxiliary energy transmitted to the energy vector is totally recovered;
recoverable auxiliary energy transmitted to the heated space
The recovered auxiliary energy transmitted to the heating medium Q gnr,aux,rvd is calculated by: aux rvd aux gnr rvd aux gnr W f
The equation \( Q_{aux} = f \cdot P \) represents the auxiliary energy transmitted to the distribution sub-system The specific value should be provided in a national annex, and in the absence of national values, a default value is specified in section A.4.1.
Recovered auxiliary energy already taken into account in efficiency data shall not be calculated for recovery again It has to be calculated for auxiliary energy need only
Measured efficiency, as defined by relevant standards, typically accounts for the heat recovered from auxiliary energy sources, including the combustion air fan, control devices, and primary pump, with the heat recovery being assessed alongside the useful output.
The recoverable auxiliary energy transmitted to the heated space Q gnr,aux,rbl is calculated by: aux rbl brm aux gnr rbl aux gnr W b f
The equation \$Q_{,,} = \cdot (1 - ) \cdot \$ represents the auxiliary energy not transmitted to the distribution sub-system, denoted as \$f_{rbl,aux}\$ The specific value should be provided in a national annex; if unavailable, a default value is specified in section A.4.1 Additionally, the temperature reduction factor, \$b_{brm}\$, which varies based on the boiler's location, must also be included in the national annex, with a default value available in section A.4.3 if national values are not provided.
7.3.6.2 Boiler thermal loss (boiler envelope)
Only the thermal losses through the boiler envelope are deemed recoverable, representing a portion of the total standby heat losses.
The recoverable thermal losses through the boiler envelope Q gnr,ls,env,rbl are calculated by: tot gnr env gnr brm corr
P ls gnr rbl env ls gnr b f t
The equation \$Q_{gnr} = \Phi_{gnr,0} \cdot (1 - f_{gnr,env}) \cdot b_{brm} \cdot t_{gnr,tot}\$ describes the thermal losses through the boiler envelope as a fraction of total standby heat losses The value of \$f_{gnr,env}\$ should be specified in a national annex, with default values provided in section A.4.2 if national values are unavailable Additionally, the temperature reduction factor \$b_{brm}\$, which depends on the boiler's location, should also be included in a national annex, with default values available in section A.4.3 Finally, \$t_{gnr,tot}\$ represents the total operational time of the boiler.
7.3.6.3 Total recoverable generation system thermal losses
The total recovered auxiliary energy Q H,gen,aux,rvd is calculated by:
= gnr, aux, rvd rvd aux, gen,
The total recoverable generation system thermal losses Q H,gen,ls,rbl are calculated by:
= gnr, ls, env, rbl gnr, aux, rbl rbl ls, gen,
Fuel input
Fuel heat input E H,gen,in is calculated according to Equation (1).
Operating temperature of the biomass boiler
The operating temperature of the boiler depends on:
type of control (taken into account by a correction factor);
technical limit of the boiler (taken into account by the temperature limitation);
temperature of the distribution sub-system connected to the generator
The effect of control on the boiler is assumed to be a varying average temperature of the heat emitters Therefore two types of boiler control are taken into account:
variable water temperature depending on the operating range
The operating temperature of the boiler is considered as
The minimum operating boiler temperature for each boiler, denoted as \$\theta_{gnr,w,min}\$, is specified in a national annex In cases where national values are not available, default values are provided in section A.2.1 Additionally, \$\theta_{H,dis,m}\$ represents the temperature for the heat distribution and storage system, if necessary, during the specified period.
Boiler cycling method
Principle of the method
This calculation method is based on the following principles
7.4.1.2 Thermal losses of the boiler
Thermal losses of the boiler are taken into account separately for the five operation periods distinguished in 7.2
During the boiler heating up operation, the following thermal losses are taken into account:
heat of flue gas of the boiler according the intermediate load;
heat losses through the boiler envelope
During the boiler heating operation, the following thermal losses are taken into account:
heat of flue gas of the boiler according the intermediate load;
heat losses through the boiler envelope at the running temperature
During the boiler cooling down operation, the following thermal losses are taken into account:
no heat of flue gas of the boiler;
heat losses through the boiler envelope
During the boiler fire bed operation, the following thermal losses are taken into account:
heat of flue gas of the boiler at fire bed load;
heat losses through the boiler envelope
During the boiler non operation, the following thermal losses are taken into account:
no heat of flue gas of the boiler;
no heat losses through the boiler envelope
Auxiliary energy is considered separately for appliances before and after the boiler:
W br is the auxiliary energy required by components and devices that are installed before the combustion chamber following the energy path (typically boiler fan, see Figure 2);
NOTE 1 Typically these components and devices are running only when the boiler is on, i.e during t gnr,on
W af is the auxiliary energy required by components and devices that are installed after the combustion chamber following the energy path (typically primary pump, see Figure 2)
NOTE 2 Typically these components and devices are running during the entire operation period of the boiler i.e during t gnr,tot = t gnr,on + t gnr,off
A portion of the auxiliary energy will be reclaimed and included in the energy balance Detailed calculation methods are accessible when sufficient information is available, while default formulas and values can be found in Annex A and Annex B.
NOTE Auxiliary energy transformed into heat and emitted to the heated space may be considered separately and is added to the recoverable heat losses
The basic energy balance of the generation sub-system (biomass boiler) is: env gnr, off ch, on ch, pmp br cmb out gen,
NOTE This is the same as equation (1) where: Q H, gen, ls = Q ch, on + Q ch, off + Q gnr, env , E H, gen, in = Q cmb and pmp br rvd aux, gen,
A schematic diagram of the energy balance of the generation sub-system is shown in Figure 2.
Input data for the calculation method
The biomass boiler is defined by key parameters including the combustion power, denoted as \$\Phi_{cmb}\$, which serves as the reference power for both design and actual values Additionally, it features a minimum combustion power, \$\Phi_{cmb,min}\$, and a reference power for heat loss factors, \$\Phi_{ref}\$, typically set equal to \$\Phi_{cmb}\$.
P’ch,on, P’ch,off , P’gnr,env heat loss factors at test conditions;
The minimum heat loss factor, denoted as P’ch,on, is evaluated at the minimum combustion power, represented by Φcmb,min Additionally, the electrical power consumption of auxiliary appliances before the boiler is indicated by Φbr, with a recovery factor of k br At minimum combustion power, the electrical power consumption of these appliances is noted as Φbr,min Furthermore, the electrical power consumption of auxiliary appliances after the boiler is represented by Φaf, accompanied by a recovery factor of k af The average boiler water temperature under test conditions for P’ch,on is denoted as θgnr,w,m,test, while the flue gas temperature at these conditions is represented by θch,test Lastly, the temperature of the test room for P’gnr,env and P’ch,off is indicated as θi,brm,test.
The difference in temperature, denoted as ∆θgnr,env,test, is calculated between the average boiler temperature (θgnr,w,m,test) and the test room temperature (θi,brm,test) under specific test conditions for P’gnr,env and P’ch,off Additionally, the n, m, and p exponents are utilized to correct the heat loss factors.
NOTE Fan assisted biomass boilers operate in a modulating mode regularly
Actual operation conditions are characterised by the following data:
The net heat output to the heat distribution sub-systems is denoted as \$Q_{gnr}\$, while the average water temperature in the boiler is represented by \$\theta_{gnr,w,m}\$ The temperature within the boiler room is indicated as \$\theta_{i,brm}\$ Additionally, the reduction factor for heat losses through the boiler envelope, which varies based on the boiler's location, is referred to as \$k_{gnr,env}\$.
NOTE All powers and the load factor FC refer to boiler input (combustion power).
Load factor
The load factor FC is the ratio between the time with the boiler in operation and the total time of boiler operation:
, , , gnr on gnr on gnr tot gnr on gnr off t t
+ (33) where t gnr,tot total time of boiler operation (h); t gnr,on time with the boiler ON (pre- and post-ventilation are not considered) (h);
NOTE 1 The boiler time in operation t gnr,on = t gnr,hup + t gnr,op (h); t gnr,off time with the boiler OFF (h)
NOTE 2 The boiler time in non operation t gnr,off = t gnr,cod + t gnr,fib + t gnr,non (h)
The load factor shall either be calculated according to the actual energy, Q gnr,out, to be supplied by the boiler or be measured (e.g by time counters) on existing systems
NOTE 3 The boiler heating up time t gnr,hup depends on:
- total mass of the boiler ( metal + refractory + insulating materials )
- net calorific value of the fuel ( logwood )
NOTE 4 The boiler cooling down time t gnr,cod depends on:
- total mass of the boiler ( metal + refractory + insulating materials )
- quality of the insulating materials of the boiler
Specific thermal losses
Specific heat losses of the boiler are given at standard test conditions Test conditions are identified by a quote
Heat losses at test conditions are expressed as a percentage (P’ch,on, P’ch,off and P’gnr,ge) of a reference power at test conditions
Test values shall be adjusted according to actual operation conditions This applies both to standard test values and to field measurements
7.4.4.2 Thermal losses through the chimney with the boiler on, P ch,on
The correction method for this loss factor takes into account the effects of:
average water temperature in the boiler;
boiler settings (power and excess air changing the heat exchange efficiency)
Actual specific thermal losses through the chimney with the boiler on P ch,on are given by:
[ ch on gnr w m gnr w m test corr ] n on ch P f FC
P’ch,on represents the percentage of heat losses through the chimney when the boiler operates under test conditions, complementing the combustion efficiency to 100% This measurement is taken with the average water temperature, θgnr,w,m,test The heat losses through the chimney, also known as flue gas loss, are expressed as a percentage of the combustion power, Φcmb.
For new systems, the manufacturer declares the value of P’ch,on, while for existing systems, it is determined by measuring combustion efficiency according to national standards or recommendations During this measurement, it is essential to also record the average water temperature, denoted as θgnr,w,m,test, and the combustion power, represented as Φcmb.
In the absence of available data, default values specified in B.2.1 will be applied The calculation report must clearly indicate the source of the data used The parameter θgnr,w,m,test represents the average water temperature in the boiler under test conditions, measured in °C, which is typically the average of the flow temperature (80 °C) and the return temperature (60 °C).
For the design of new systems, θgnr,w,m,test is the value declared by the manufacturer For existing systems, θgnr,w,m,test is measured with combustion efficiency
In the absence of available data, default values can be found in section B.2.1 The calculation report must clearly indicate the data source The average water temperature in the boiler at actual conditions, denoted as \$\theta_{gnr,w,m}\$ in °C, is calculated as the average of the flow and return temperatures The correction factor for \$P'_{ch,on}\$, represented as \$f_{corr}\$, has default values provided in B.2.1 Additionally, the load factor exponent, denoted as \$n\$, also has default values specified in B.2.1.
NOTE 1 The factor FC n takes into account the reduction of losses with high intermittencies, due to a lower average temperature of the flue gas (higher efficiency at start) An increasing value of n corresponds to a higher value of c mass, defined as the ratio between mass of the heat exchange surface between flue gas and water and nominal combustion power of the boiler
NOTE 2 Equation (34) takes into account variation in combustion efficiency depending on average temperature of water in the generator by a linear approximation The assumption is, that temperature difference between water and flue gas is approximately constant (i.e a 20 °C increase of average water temperature causes a 20 °C increase of flue gas temperature) A 22 °C increase of flue gas temperature corresponds to 1 % increase of losses through the chimney, hence the default value 0,045 for f corr Equation (34) does not include the effect of any latent heat recovery
NOTE 3 Equation (34) does not take into account explicitly the effect of varying air/fuel ratio The default constant 0,045 is valid for standard excess air (3 % O2 in flue gas) For new systems, a correct setting is assumed For existing systems, the air/fuel ratio contributes to P’ch,on If required, the constant 0,045 should be recalculated according to the actual air/fuel ratio
NOTE 4 Equation (34) does not take into account explicitly the effect of varying combustion power If the combustion power is significantly reduced, the procedure for existing systems shall be followed (i.e P ch,on needs to be measured)
7.4.4.3 Thermal losses through the boiler envelope, P gnr,env
Actual specific thermal losses through the boiler envelope P gnr,env are given by: m test brm i test m w gnr brm i m w gnr env gnr env gnr env gnr P k FC
P’gnr,env represents the heat losses through the boiler envelope under test conditions, expressed as a percentage of the reference power, Φref, which typically refers to the nominal combustion power of the boiler.
For the design of new systems, P’gnr,env is the value declared by the manufacturer
In the absence of available data, default values specified in section B.2.2 will be applied It is essential to clearly indicate the data source in the calculation report, including the kg gnr,env reduction factor, which considers the boiler's location.
The recovery of thermal losses is considered a reduction in total losses Default values for the test room temperature (\(θ_{i,brm,test}\)) and the actual room temperature where the boiler is installed (\(θ_{i,brm}\)) are provided in section B.2.2 Additionally, the exponent for the load factor (FC) is specified in B.2.2, depending on the parameter \(c_{gnr}\), which is defined as the ratio of the total weight of the boiler (including metal, refractory, and insulating materials) to the nominal combustion power (\(Φ_{cmb}\)) of the boiler.
NOTE 1 The factor FC m takes into account the reduction of heat losses through the boiler envelope if the boiler is allowed to cool down during non operation cycle In all cases m = 0 inhibits this correction
NOTE 2 It is assumed that heat losses through the envelope are related to the temperature difference between the average water temperature in the boiler and the temperature of the boiler surroundings The relation is assumed to be linear (heat conduction through the boiler insulation)
NOTE 3 P’gnr,env can be determined as the difference between the combustion efficiency and the net efficiency of the boiler at test conditions (continuous operation)
Recovery of losses through the boiler envelope is taken into account as a reduction of total losses by the reduction factor k gnr,env
To calculate the total thermal losses of the boiler envelope, denoted as \$P_{gnr,env,tot}\$, one can derive it from the heat losses measured under test conditions, represented as \$P'_{gnr,env}\$, using the formula: \$m_{test} \cdot brm_{i \, test} \cdot m_{w \, gnr} \cdot brm_{i \, m} \cdot w_{gnr \, env}\$.
, gnr tot , env , gnr FC
= θ θ θ θ (36) and determine the actual recoverable thermal losses factor, P gnr,env,rbl by:
, env rbl gnr env tot gnr env gnr P k
P = ⋅ − (37) where k gnr,env reduction factor according to B.2.2
7.4.4.4 Thermal losses through the chimney with the boiler off, P ch,off
This thermal loss takes into account the stack effect of the chimney, which causes a flow of cold air through the boiler
A correction based on the average water temperature in the boiler and the surrounding boiler room temperature is necessary The maximum energy loss during each boiler off period is determined by the heat stored in both the metallic components and the water within the boiler Consequently, the load factor is influenced by the boiler's heat capacity.
Actual specific thermal losses through the chimney when the burner is off P ch,off are given by: p test brm i test m w gnr brm i m w gnr off ch off ch P FC
Total thermal losses
Thermal losses through the chimney (flue gas losses) with the boiler on are given by: on gnr cmb on ch on ch P t
Thermal losses through the chimney with the boiler off are given by: off gnr ref off ch off ch P t
Thermal losses through the boiler envelope are given by:
, ref gnr on gnr off env gnr env gnr P t t
The total generation thermal losses are given by the sum of the total thermal losses of each biomass boiler:
= gnr, ls ( ch, on ch, off gnr, env ) ls gen,
Auxiliary energy
For each auxiliary device of the biomass boiler, the following data shall be determined:
Electrical power consumption P gnr,aux,i Values can be:
or default values calculated according to B.3
The source of data shall be clearly stated in the calculation report
Running time t on,aux,i, as a function of load factor FC where appropriate (i.e burner auxiliaries)
Variable electrical power consumption should be approximated by an equivalent constant average electrical power consumption
The total auxiliary energy required by the boiler is given by:
= i gnr, aux, i on, aux, i aux gnr, P t
Recoverable system thermal losses
The recoverable auxiliary energy transmitted to the heated space Q gnr,aux,rbl is calculated by: aux rbl brm aux gnr rbl aux gnr W b f
The equation \$Q_{,,} = b_{brm} \cdot (1 - f_{rbl,aux}) \cdot Q\$ describes the heat output of a boiler, where \$b_{brm}\$ is the temperature reduction factor that varies by boiler location This value should be specified in a national annex, and in its absence, default values are provided in section B.3 Additionally, \$f_{rbl,aux}\$ represents the portion of nominal electrical energy not delivered to the distribution sub-system, which should also be detailed in a national annex, with default values available in B.3 If the boiler's performance has been certified, this can be factored into the calculations.
7.4.7.2 Recoverable thermal loss (boiler envelope)
If not otherwise specified in a national annex, Q gnr,env,rbl = 0
7.4.7.3 Total recoverable generation system thermal loss
The total recoverable generation system thermal losses Q H,gen,ls,rbl are given by the sum of the recoverable system thermal loss of each biomass boiler:
= gnr, env, rbl gnr, aux, rbl rbl ls, gen,
Calculation procedure for a modulating biomass boiler (fan assisted)
The calculation procedure and an example are given in Annex E
Additional formulas and default values for parametering the case specific boiler efficiency method
Information on the method
Basic assumptions and intended use
This methodology assumes that thermal losses and auxiliary power consumption are linearly dependant on boiler load in two ranges:
from intermediate load to nominal (maximum) load
The intermediate load for fan-assisted biomass boilers is defined based on manufacturer testing, typically assessed at 50% of the nominal load Regular testing ensures consistent performance and reliability.
It is also assumed that efficiencies determined according to testing standards can be corrected using linear functions of actual boiler operating temperature and the boiler installation room temperature.
Known approximations
The intermediate load should be the minimum power with boiler on
The installation room temperature significantly affects boiler efficiency, particularly at minimum load and during standby conditions While its impact is often overlooked, it plays a crucial role in influencing standby heat losses, thereby affecting performance in the range from 0 to intermediate load.
Boiler efficiencies and stand-by heat losses
Default values for boiler efficiency at full load and intermediate load as a function of the
The boiler efficiency at full load as a function of the boiler power output is given by:
The boiler efficiency at intermediate load as a function of the boiler power output is given by:
Pn P gnr c c η (A.2) where Ф Pn,ltd nominal power output, in W, limited to a maximum value of 400 kW
For boilers with a nominal power output exceeding 400 kW, the value of 400 kW is utilized in Equations (A.1) and (A.2) The coefficients c 1, c 2, c 3, and c 4 are specified in Tables A.1 and A.2.
Table A.1 — Parameters for calculation of boiler efficiency and temperature limitation
Fan assisted biomass boiler before 1978 80,0 2,0 75,0 3,0 50
NOTE Test temperatures are given in Table A.4 and Table A.5
Table A.2 — Parameters for calculation of boiler efficiency and temperature limitation based on EN 303-5
Stand-by heat losses
Default value for the stand-by heat losses Φ gnr,ls.P0 as a function of the boiler power output is given by:
= Φ (A.3) where Ф Pn nominal power output in W; ФPn,ltd nominal power output, in W, limited to a maximum value of 400 kW
If the nominal power output of the boiler is higher than 400 kW, then the value of 400 kW is adopted in Equation (A.3); c 5, c 6 parameters given in Table A.3
Table A.3 — Parameters for calculation of stand-by heat losses
Fan assisted biomass boiler before 1978 9,0 –0,28 50
Correction factor taking into account variation of efficiency depending on boiler average
Table A.4 — Default values for full load correction factor f corr,Pn
Boiler average water temperature at boiler test conditions for full load θ gnr,w,test,Pn
Table A.5 — Default values for intermediate load correction factor f corr,Pint
Boiler average water temperature at boiler test conditions for intermediate load θ gnr,w,test,Pint
Correction factor fcorr,Pn may be calculated using efficiency data from additional tests performed at a lower average water temperature, using the following equation:
Pn test w gnr add Pn test w gnr add Pn
= − (A.4) where η Pn full load efficiency at standard test conditions with average water temperature θ gnr,w,test,Pn ; η Pn,add full load efficiency with average water temperature θ gnr,w,test,Pn,add
Correction factor f corr,Pint may be calculated using efficiency data from additional tests performed at a higher average water temperature, using the following equation: int , , , int,
P test w gnr add P test w gnr add P
= − (A.5) where η Pint intermediate load efficiency at standard test conditions with average water temperature θ gnr,w,test,Pint ; η Pint,add intermediate load efficiency with average water temperature θ gnr,w,test,Pint,add
Auxiliary energy
Default value for the power consumption of auxiliary equipment is calculated by: n
, (A.6) where Ф Pn nominal power output in W; c 7, c 8, n parameters given in Table A.6
Table A.6 — Parameters for calculation of power consumption of auxiliary equipment
Recoverable boiler thermal losses
Auxiliary energy
The default value for the auxiliary energy transmitted to the distribution sub-system, denoted as \$f_{rvd,aux}\$, is 0.75 The portion of auxiliary energy transmitted to the heated space, represented as \$f_{rbl,aux}\$, is calculated using the formula: \$f_{rbl,aux} = 1 - f_{rvd,aux}\$ (A.7).
Thermal losses (boiler envelope)
The part of stand-by heat losses attributed to heat losses through the boiler envelope is given by f gnr,env Default values of f gnr,env are given in Table A.7
Table A.7 — Part of stand-by heat losses attributed to losses through the boiler envelope
Default data according to boiler location
Table A.8 — Temperature reduction factor and default installation room temperature
Additional formulas and default values for parametering the boiler cycling method
Information on the method
Basis assumptions and intended use
This method is intended for use with existing boilers, where data are declared according to relevant standards
This methodology is based on a physical analysis of losses (indirect method) and takes into account two operating conditions:
boiler in non operation ( off or fire bed )
This methodology is suitable for modulating boilers in operation or in non operation
This annex presents data based on net calorific values (H i) If it is necessary to calculate losses using gross calorific value (H s), please follow the procedure outlined in section 4.6.
Known approximations
Losses from a non-operational boiler chimney are difficult to quantify, but newer boilers equipped with air intake closures during standby mode experience significantly reduced loss factors.
Default specific losses
Default data for calculation of thermal losses through the chimney with boiler on
Table B.1 — Default value of θθθθ gnr,w,m,test , P ’ ch,on and f corr
Table B.2 — Default value of exponent n
NOTE c mass in kg/kW is the ratio between the mass of the heat exchange surface between flue gas and water and nominal combustion power of the boiler.
Default values for calculation of thermal losses through the boiler envelope
The default losses through the boiler envelope P'gnr,env are given by:
P (B.1) where c 1, c 2 parameters given in Table B.3; Φcmb boiler nominal combustion power in W
Table B.3 — Default value of parameters c 1 and c 2
Well insulated, high efficiency new boiler 1,72 0,44
Old boiler with average insulation 6,90 1,76
Table B.4 — Default value of reduction factor k gnr,env , test room temperature θ i,brm,test and installation room temperature θ i,brm
Boiler type and location k gnr,env
Boiler installed within the heated space 0,1
Atmospheric boiler installed within the heated space 0,2 20
Boiler installed within a boiler room 0,7 13
Boiler installed outdoors 1,0 External temperature
Table B.5 — Default value of exponent m
The primary pump is always running 0,0
The primary pump stops after the boiler turns to non operation 1 to 3 0,10
NOTE c gnr in kg/kW is the ratio between the total weight of the boiler (metal + refractory materials + insulating materials) and the nominal combustion power of the boiler.
Default values for calculation of thermal losses through the chimney with the boiler off
Table B.6 — Default value of P ' ch,off
Biomass fired boiler with the fan before the combustion chamber and automatic closure of air intake with burner off 0,2
Biomass fired boiler with the fan before the combustion chamber and no closure of air intake with burner off:
Table B.7 — Default value of exponent p
The primary pump is always running 0,0
The primary pump stops after the boiler turns to non operation
0,10 0,05 NOTE c gnr in kg/kW is the ratio between the total weight of the boiler (metal + refractory materials + insulating materials) and the nominal combustion power of the boiler.
Default values for calculation of auxiliary energy
The default auxiliary power consumption P br and P pmp are given by cmb x c c
P = 3 + 4 ⋅ Φ /1 000 (B.2) where Φcmb is the boiler nominal combustion power in W
Table B.8 — Default value of c 3 and c 4 for the calculation of electrical power consumption of auxiliary devices
NOTE If there is no primary pump, then P pmp = 0
The recoverable portion of auxiliary energy for space heating, denoted as \$f_{rbl,aux}\$, is calculated using the formula: \$f_{rbl,aux} = 1 - f_{rvd,aux}\$, where \$f_{rvd,aux}\$ represents the amount of auxiliary energy that is recovered and transferred to the distribution sub-system.
Default value of f rvd,aux is given in Table B.9 along with default values of temperature reduction factor according to boiler location
Table B.9 — Default value of temperature reduction factor b brm and auxiliary energy recovery factor f rvd,aux
Auxiliary energy recovery factor f rvd,aux
Additional default data for modulating burners
The default minimum combustion power of the boiler is given by: Φcmb,min = Φcmb ã f min (B.4) where f min parameter given in Table B.10; Φcmb boiler nominal (maximum) combustion power
Table B.10 — Parameter f min for modulating burners
Table B.11 — Default value of θθθθ gnr,w,m,test,min and P ’ ch,on,min
The default auxiliary power consumption P br,min is calculated with Equation (B.2) using:
Φ cmb,min instead of Φ cmb;
Table B.12 — Default value of c 3 and c 4 for the calculation of electrical power consumption of auxiliary devices at minimum combustion power
Storage systems for biomass combustion systems
General
Accumulator storage system
According to EN 303-5, it is advisable to enhance the boiler system with manual stocking through an accumulator storage system when the ratio of the nominal heat output of the boiler (\$Ф_{gnr,nom}\$) to the design heat load (\$P_{bg,nom}\$) exceeds 1.5.
The main objective of an accumulator storage system for the boiler is to:
store the heat between the operation cycles;
improve the heating comfort for the user
A further objective is, as with a load balancing storage system, to improve the operation conditions regarding thermal efficiency and environmental impact as well
An accumulator storage system comprises the following components:
distribution piping between the boiler and the accumulator storage tank, including circulation pump;
Load balancing storage system
The object of a load balancing storage system for boilers is to improve the operation conditions regarding thermal efficiency and environmental pollution by:
reduction of the start and stop cycles during the operation of the automatic fired boilers;
extension of the minimum running time between the start operation and stop operation
Load balancing storage systems are essential for boilers equipped with automatic stocking These systems share similar components with accumulator storage systems; however, the sizing of the storage tank differs significantly.
Sizing of storage systems for biomass combustion systems
Sizing of the volume of the accumulator storage tank
The volume of the accumulator storage tank V acc,ta is determined by:
, nom bg nom gnr nom gnr on gnr ta acc t P
= (C.1) where t gnr,on operation time of the boiler (h); Φ gnr,nom nominal heat output of the boiler(s) (kW);
P bg,nom (design) heat load of the building (kW)
Default value for the volume of the accumulator storage tank V acc , ta = 50 × P bg , nom (litres) (C.2)
Sizing of the volume of the load balancing tank
The volume of the load balancing storage tank V lob,ta is calculated by:
V lob,ta = ( Q gnr,100 × t gnr , op,min × 14,33 ) / ∆θ gnr,op,stst - V gnr,he,med - V pip,dis,he,med (C.3) where
Q gnr,100 nominal heat output of the boiler(s) kW; t gnr,op,min minimum time between the start and stop of the operation cycle min;
∆θ gnr,op,stst temperature difference between start operation and stop operation of the boiler K;
V gnr,he,med volume of the heating medium of the boiler litres;
V pip,dis,he,med volume of the heating medium of the distribution piping before control devices litres
Default value for the volume of the load balancing storage tank V lob , ta = 25 × P bg , nom (litres) (C.4)
System thermal losses of storage systems
Thermal losses
C.3.1.1 Thermal losses of the storage tank
The calculation of thermal losses for the accumulator or load balancing storage tank, denoted as \( Q_{\text{sto,ls,ta}} \), follows a methodology akin to that used for domestic hot water storage tanks Key values are provided for accurate assessment.
information by the manufacturer (standby value);
calculation procedure according to the specification for storage tanks (see EN ISO 12241)
C.3.1.2 Thermal losses of the storage piping
The calculation of thermal losses for accumulator or load balancing storage piping, denoted as \$Q_{sto,ls,pip}\$, follows a methodology similar to that used for storage tanks designed for domestic hot water Key values are provided for accurate assessment.
information by the manufacturer (standby value);
calculation procedure according to the specification for the domestic hot water storage piping
The total thermal losses of the accumulator or load balancing storage system Q sto,ls are calculated by:
Q sto,ls = Q sto,ls,ta + Q sto,ls,pip (C.5)
Auxiliary energy of the circulation pump
The auxiliary energy of the circulation pump W sto,aux,pu is calculated by:
The equation for the power consumption of a circulation pump is given by \$W_{sto,aux,pu} = f_{corr,ci} \times \Phi_{el,pu} \times t_{ci}\$, where \$f_{corr,ci}\$ is the correction factor for running time, with a default value of \$f_{corr,ci} = 0.12\$, \$\Phi_{el,pu}\$ represents the nominal output of the circulation pump in kilowatts (kW), and \$t_{ci}\$ denotes the running time of the circulation pump in hours (h).
The recoverable auxiliary energy of the circulation pump Qsto,aux,pu,rbl is calculated by:
Q sto,aux,pu,rbl = W sto,aux,pu × f sto,sys (C.7) where f sto,sys factor considering the operation conditions of the storage system
Default value for f sto,sys = 0,75
Calculation procedure with an example for biomass boiler with stocking by hand - Case specific boiler efficiency method
Type of biomass combustion system Standard boiler, constant boiler running temperature, no accumulating storage tank
Type of control Modulating, fan assisted
Nominal power ( 100 % load ) Ф Pn = 36,0 kW
Full load efficiency based on test results Test value η gnr,Pn = 88 %
Intermediate part load Test value Ф Pint = 18,0 kW
Intermediate part load efficiency Test value η gnr,Pint = 90 %
Minimum boiler temperature Θ gnr,w,min = 60 °C
Energy supplied to the distribution system
EN 15361-3-2 Q gnr,out = 6 000 kWh/ month
Calculation period 1 month, t gnr,tot = t ci = 30 × 24 = 720 h
Boiler location Inside boiler room
Boiler room temperature Table A.8 Θ i,brm = 13 °C
Average water temperature in the boiler Θ gnr,w,m = 65 °C
Correction factor for 100% load Table A.4 f corr,Pn = 0,04 % / °C
Boiler average water temperature at test conditiones Table A.4 Θ gnr,w,test,Pn = 70 °C
100% load Equation (12) η gnr,Pn,corr = 88,0 + 0,04 × ( 70 - 65 ) = 88,2 %
Corrected boiler thermal loss at
100% load Equation (13) Ф gnr,ls,Pn,corr = ((100 – 88,2 ) / 88,2)) × 36 = 4,82 kW
Correction factor for intermediate load Table A.5 f corr,Pint = 0,05 % / °C
Boiler average water temperature at test conditiones Table A.5 Θ gnr,w,test,Pint = 70 °C
Corrected boiler efficiency at intermediate load
Equation (14) η gnr,Pint,cor = 90,0 + 0,05 × ( 70 - 65 ) = 90,25 % Corrected boiler thermal loss at intermediate load Equation 15 Ф gnr,ls,Pint,corr = ((100 – 90,25) / 90,25)) × 18 = 1,94 kW
Parameters for fire bed (stand- by) operation
Thermal loss at 0% load (fire bed operation ) Equation A.3 Ф gnr,ls,P0 = 36 × (8,5/100) × (36 000/1 000) -0,4
Corrected boiler thermal loss at
Table A.3 Ф gnr,ls,P0,corr = 0,73 × ((65 – 13)/(50)) 1,25 = 0,73 × 1,05 = 0,77 kW Boiler average power Equation (9) Ф gnr,out = 6 000 / 720 = 8,33 kW
Specific load ratio Equation (10) β gnr = 8,33 / 36 = 0,23
Power output at specific load ratio Equation (17) Ф Px = 36,0 × 0,23 = 8,33 kW
Boiler thermal loss at specific heat load Equation (18) Ф gnr,ls,Px, = (8,33/18) × (1,94 – 0,77) + 0,77
Total boiler thermal loss Equation (20) Q gnr,ls = 1,31 × 24 × 30 = 943,2 kWh/month
Recoverable boiler thermal losses Equation (28),
Parameters, power consumption of auxiliaries at intermediate load Table A.6 c 7 = 0, c 8 = 15, n = 0,48
Power consumption of auxiliary equipment at intermediate load Equation (A.6) P aux,Pint = 0 + 15 x 18 0,48 = 60 W
Parameters, power consumption of auxiliaries at fire bed operation
Power consumption of auxiliary equipment at fire bed operation Equation (A.6) P aux,P0 = 15 + 0 = 15 W
Power consumption of auxiliary equipment at specific heat load
Auxiliary energy Equation (22) W gnr,aux = 35,7 × 720 + 0 = 25,7 kWh/month
Recovered auxiliary energy to the heating medium
Equation 26, A.4.1 Q gnr,aux,rvd = 25,7 × 0,75 = 19,3 kWh/month
Recoverable auxiliary energy to the heated space Equation (27),
A.4.1, A.4.3 Q gnr,aux,rbl = 25,7 × (1 – 0,3) × 0,25 = 4,5 kWh/month
Fuel heat requirement Equation (1) E gnr,in = 6 000 - 19,3 + 943,2 = 6 923,9 kWh/month
Total system thermal losses Q gnr,ls,tot = Q gnr,ls + (W gnr,aux - Q gnr,aux,rvd)
Total recoverable system thermal losses
Equation (30) Q gnr,ls,rbl = 291,1 + 4,5 = 295,6 kWh/month
Monthly efficiency of the biomass boiler η gnr,m = 1 - Q gnr,ls / (Q gnr,out + Q gnr,ls )
Calculation procedure with an example for biomass boiler with stocking by hand (Cycling method)
Type of biomass combustion system Standard boiler, constant boiler running temperature, no accumulating storage tank
Type of control Modulating, fan assisted
Nominal power ( 100 % load ) Ф cmb = Ф ref = 36,0 kW
Minimum combustion power Test value Ф cmb,min = 18,0 kW
Volume burning chamber Test value V cham = 146 litres = 0,146 m 3
Specific heat loss through the chimney with boiler ON ( Flue gas loss ) at test conditions
Specific heat loss through the chimney with boiler OFF (flue gas loss) at test conditions
Average water temperature in the boiler at test conditions Table B.1 Θ gnr,w,m,test = 70 °C
Room temperature at test conditions
Parameters for default heat losses through boiler envelope
Specific heat loss through the boiler envelope Equation (B.1) P'gnr,env = c 1 – c 2 × ( log Ф Pn /1 000 )
Energy supplied to the distribution system EN 15316-3-2 Q gnr,out = 6 000 kWh/month
Caloric net value ( log wood ) H i,fuel = 1 850 kWh/rm
Heat output each filling Ф cham
= V cham × H i,fue × (100 – P’ch,on – P’gnr,env) / 100
= 232,0 kWh Interval of chamber filling t gnr,fill = 24 h
Operation period ON (min load) t gnr,on = Ф cham / Ф cmb,min = 232,0 / 18 = 12,9 h Operation period OFF (fire bed) t gnr,off = t gnr,fill - t gnr,on = 24,0 – 12,9 = 11,1 h
Boiler location Inside boiler room
Boiler room temperature Table B.4 Θ i,brm = 13 °C
Running temperature of the boiler Θ gnr,w,m = 65 °C
Load factor during boiler ON
(min load) Equation (33) FC gnr,on = 18,0 / 36,0 = 0,5
Load factor during boiler fire bed operation
Correction factor for P’ch,on Table B.1 f corr = 0,045 % / °C
Exponent for load factor Table B.2 n = 0,1
Specific thermal loss through the chimney with the boiler ON
Thermal loss through the chimney with boiler ON
= 25,5 kWh/day Exponent for load factor Table B.5 m = 0,1
Reduction factor Table B.4 kgnr,env = 0,7
Specific thermal loss through the envelope at minimum load Equation (35) P gnr,env = 2,1 × 0,7 × (65 – 13)/(70 – 20) × 0,5 0,1
Thermal loss through the boiler envelope at minimum load and fire bed operation
Equation (41) Q gnr,env = ( 1,4 / 100 ) × 18 × 24 = 6,0 kWh/day
Exponent for load factor Table B.7 p = 0,1
Specific thermal loss through the chimney with the boiler OFF
Thermal loss through the chimney with boiler OFF Equation (40) Q ch,off = ( 1,2 / 100 ) × 18,0 × 11,1 = 2,4 kWh/day
Total boiler thermal loss Equation (42) Q gnr,ls = ( Q ch,on + Q ch,off + Q gnr,ge ) × 30
7.4.6.2 Q gnr,ls,env,rbl = 0 kWh/month
Default values for the electric power consumption of auxiliary devices
Specific electric power of the auxiliary equipment for tON
Specific electric power of the auxiliary equipment for tOFF
Total auxiliary energy Equation (43) W gnr,aux = ( 87 × 12,9 + 15 × 11,1 ) × 30
= 38,6 kWh/month Recovered auxiliary energy Table B.9 Q gnr,aux,rvd = 38,6 × 0,8 = 30,9 kWh/month
Recoverable auxiliary energy to the heated space Equation (44),
Fuel heat requirement Equation (1) E gnr,in = 6 000 – 30,9 + 1 017,0
Total system thermal losses Q gnr,ls,tot = Q gnr,ls + ( W gnr,aux - Q gnr,aux,rvd )
Total recoverable system thermal losses Equation (45) Q gnr,ls,rbl = 0 + 5,4 = 5,4 kWh/month
Monthly efficiency of the biomass boiler η gnr,m = 1 - Q gnr,ls / (Q gnr,out + Q gnr,ls )
[1] Council Directive 92/42/EEC of 21 May 1992 about the efficiency requirements of the new gas or oil boilers
[2] EN ISO 15927-1, Hygrothermal performance of buildings — Calculation and presentation of climatic data — Part 1: Monthly means of single meteorological elements (ISO 15927-1:2003)
[3] ISO 13602-2, Technical energy systems — Methods for analysis — Part 2: Weighting and aggregation of energywares
[4] EN ISO 13790, Thermal performance of buildings — Calculation of energy use for space heating and cooling (ISO 13790:2004)
[5] CEN/TS 14588:2003, Solid biofuels — Terminology, definitions and descriptions
[6] CEN/TS 14961, Solid fuels — Fuel specification and classes
[7] EN 15603, Energy performance of buildings — Overall energy use and definition of energy ratings