Evaporative Air-Conditioning phần 6 potx

Solar Evaporative Air-Conditioning Because evaporative air-conditioners require relatively little energy, and because the presence of strong sunshine often coincides with the need for co

Solar Evaporative Air-Conditioning

Because evaporative air-conditioners require relatively little energy, and because the presence of strong sunshine often coincides with the need for cooling, a link between EAC and solar energy appears attrac-tive (see Figures 6.1 and 6.2 for a schematic diagram and a picture) Only a few suppliers offer solar-powered air-conditioners, however, even in the southwestern United States, the heart of the EAC indus-try Companies supplying these devices apparently aim for other markets, such as developing countries where grid electricity is not yet common

The Market

It is apparent from Table 6.1 that only a very few sources are suppliers of solar EAC Moreover,

inquir-Figure 6.1 A Solar-Powered Evaporative Air-Conditioner

Solar (PV) panel array

Evaporating pad media

Air distribution baffle Ambient air in

Water storage with recirculating pump Axial fan t Supply air out

Source: ECI.

37

38 Evaporative Air-Conditioning: Applicationsfor Environmentally Friendly Cooling

Table 6.1 Available Packaged Solar Evaporative Air-Conditioning Equipment

Required solar Approximate cost

Source: Authors.

ies of suppliers indicate that only a few units have been sold so far (probably only a few hundred, worldwide, to date) The attractiveness of solar EAC depends largely on the availability and cost of electric power Because photovoltaic (PV) power may cost US$0.25/kWh or more, compared with US$0.10/kWh for power from the grid, PVs are most likely to be cost effective where grid power does not yet reach Nevertheless, solar evaporative air-conditioning is a proven technology that can be very useful and efficient in such circumstances

Optimizing Evaporative Air-Conditioning Design for Solar Operation

Because of the high investment cost of solar panels (90 percent of the cost of solar EAC is the cost of the solar array), it is important that the energy requirement of the air-conditioner be as low as possible Ordinary evaporative air-conditioners are not really designed for minimizing energy need as electric power from the grid is inexpensive This means that for evaporative air-conditioners to be suitable for solar operation, they should really be redesigned to minimize power consumption

Important points will be the efficiency of the fan (axial rather than centrifugal), motor efficiency, reduced pad resistance (larger area) and a high-efficiency circulation pump At present, it seems that manufacturers simply replace the AC motors with DC motors or add an inverter to make conventional air-conditioners suitable for solar power

Such measures will make the cooler more expensive but sharply reduce the investment in the solar array and thus the total system cost Obvious areas for improving the energy efficiency of EAC for solar power are presented in Table 6.2

Table 6.2 Design Measures to Optimize Evaporative Air-Conditioningfor Solar Power

magnet motor

radial type

reduce air velocity Overall potential reduction

Source: Authors.

Solar Evaporative Air-Conditioning 39

Figure 6.2 Evaporative Cooler Coupled with Solar Power (System installed by a homeowner in Chaparral, New Mexico, USA)

Source: ECI

Introduction and Local Manufacture

in Developing Countries

Maintenance

Unlike conventional air-conditioners and fans, evaporative air-conditioners require simple but relatively frequent maintenance and replacement of parts Some parts, such as the aspenwood pads, need to be replaced after 6 to 12 months, depending on the local water quality This means that EAC marketing must

be accompanied by an after-sale service network and that where sales are just being established, this after-sale network will need to be set up as well

Installation and Sizing

Another important difference between EAC as compared with fans and vapor-compression air-condi-tioners is that EAC requires some knowledge about airflow direction, distribution, and evacuation for the cooling to be effective In some cases (e.g., Tunisia, Bangladesh) EACs of the spot-cooling (trolley) type were introduced, but because of lack of proper instruction they were used in closed rooms as if they were vapor-compression air-conditioners Since EACs require outside air flow, the units did not function properly, causing general disillusionment and failure in the marketplace The lesson is clearly that EAC must be introduced with adequate and honest information to the users, and replacement materials and trained service personnel should be ensured

Manufacturing Requirements

EAC is essentially a low technology and can be wholly or partially produced in developing countries, depending on the existing industrial base In India and Pakistan, for example, large numbers of units are being produced entirely locally (see Figure 7.1)

41

42 Evaporative Air-Conditioning: Applications for Environmentally Friendly Cooling

Cabinet Sheet metal working In house

Louvers Sheet metal working In house

Grill Sheet metal or wood In house or purchased Motor Motor manufacturing Buy from local supplier or

import directly Fan Metal stamping, aluminum Buy from local supplier

casting or plastic molding or import directly

Pad:

Rigid pad Highly specialized Buy from local supplier

or import directly Wood wool or other locally Cottage industry Buy from local supplier available pad material

Source: Authors.

K.1

F-f -._ _ 3

Suc; .S Foser

Introduction and Local Manufacture in Developing Countries 43

Certain components are easier to make than others Electric motors, fans, and water circulation pumps can only be produced in countries with a reasonably large industrial base, such as India, Pakistan, and China Yet even where such items cannot yet be made locally, they can be imported, and their source should not be of vital consequence to most manufacturers of coolers because they will be purchasing them for assembly in any case Table 7.1 gives an overview of the items that are needed for building and assembling EACs and who makes or supplies the components

It follows from Table 7.1 that the production of coolers is essentially sheet metal working, while the mechanical items are usually purchased Such sheet-metal work can be done on a small scale and re-quires very little in the way of investments in machines, molds, or accommodation In short, EACs are a good product for small-scale entrepreneurs as well as for larger industries

Know-How

Although the production of EACs itself is rather straightforward, a need remains for a good design if the cooler is to work satisfactorily A "good design" means that motor, fan, pump, and pad should be well matched to obtain good performance, energy efficiency, and cost effectiveness This industry-specific know-how often falls short of the mark in developing countries where EAC is already popular, and it may be lacking altogether in countries where local production is yet to be initiated

Local enterprises that wish to obtain EAC know-how have basically two options:

* Establish a joint venture with an EAC manufacturer in the West

* Secure training from independent experts

Commercial Evaporative Air-Conditioning

The principle of evaporative air-conditioning is used not only in residential coolers but also in numerous commercial installations Direct EAC is used in commercial and industrial applications such as schools, greenhouses, buses, laundries, warehouses, factories, kitchens, and poultry houses Direct and indirect EACs are also used to provide comfort cooling in many buildings such as schools, libraries, and offices

Commercial versus Residential Cooling

Many commercial cooling applications are quite different from comfort cooling Comfort cooling en-hances the well-being of individuals living in homes, working in offices, and so on, in areas where ambi-ent temperatures are high The use of EAC for comfort cooling thus depends partly on the type of climate and the time of the year and partly on the needs of people for "comfort."

In many commercial cooling applications a factor additional to the type of climate and the time of year may well be present That is, the presence of an additional heat source in the form of machines, ovens, dryers, animals, and so on In such applications, cooling systems often must be sized and de-signed to work for the whole year For example, kitchens often need cooling even during winter Another important aspect of commercial EAC, in certain places where a heat source can be cooled directly (e.g., spot-cooling in a manufacturing plant), is the air stream

Another difference between commercial cooling and comfort cooling with EAC is that in commer-cial applications EAC can play a significant role that VAC systems can do only with difficulty or great expense The best example is that of cooling towers in power plants Moreover, in some agricultural applications EAC is the only realistic alternative; in greenhouses, for example, VAC would be extremely expensive to operate Similarly, in horticulture and floriculture, EAC is useful precisely because it adds moisture to the air Because it is an "air-washer," EAC may have distinctive advantages in other appli-cations as well Although in some appliappli-cations-such as in hotels, restaurants, commercial laundries, and kitchens-only the VAC options are typically considered But managers of such facilities should compare VAC and EAC systems and assess the potential of EAC properly before making decisions on investments EAC's advantages of ventilation and direct cooling may make it the most appropriate and effective solution

45