Selection of a Home Heating System.

Many factors should be considered before one selects the type of heating system and fuel for the home. There are considerable variances in fuel availability, comparative costs, and the compe­tence of contractors in installing the equipment. These factors may dictate a decision independent of any theoretical comparisons.

In most regions a warm-air system has the lowest purchase and installation cost, an electric heating system ranks second, and a hydronic system has the highest purchase and installation cost. The efficiency in using an energy source is about 80% for gas, slightly lower for oil, and close to 100% for electricity.

Comparative fuel and electric costs are important, but these are not always conclusive factors. Quantity discounts for use of fuel and electricity must be determined. Also, concurrent energy uses, such as domestic water heating, cooking, clothes drying, and electric lighting, affect overall rates and total costs. In general, the seasonal operating cost for warm-air and hydronic systems using gas as the fuel is about the same as the cost of systems using oil as the fuel. The seasonal operating cost of electric systems is higher than that for systems using gas or oil.

All types of modern heating systems warm-air, hydronic, and electric are capable of supplying highly satisfactory heating performance when properly designed and installed. Conversely, any system can be disappointing when it is im­properly designed or installed.

Future Trends. The future development of home heating systems will be affected by the continuing availability of gas and oil, the future cost of electric energy, and the development of new heating techniques.

Public awareness of the evils of air pollution will certainly have an effect on the future design and use of heating systems using coal, gas, or oil as the fuel. There may be a more widespread use of high-intensity radiant heaters because of their instant response and their ability to heat objects directly. The heat pump seems to have an assured place for the future because of its ability to provide both heating and summer air conditioning and to use electricity effectively. A more spectacular development might come from the thermoelectric heat pump, which is an all-electric device that works on the same principle as the thermocouple.

Solar heating is technically possible but eco­nomically unacceptable in most regions. Solar energy collectors are too large, too expensive, and possibly too displeasing as' a part of house architecture. With regard to the use of atomic energy for space heating, it appears likely that atomic energy applications will be limited to large central stations for the production of elec­tric power, which in turn could be used for home heating.

Unit III air coditioning and ventilating

Text 1.

Cooling Systems

The cooling of atmospheres in low–rise residential build­ings is often done locally with unit air conditioners, which penetrate the exterior wall of the space to be cooled; this permits the intake of fresh air when desired and the ejec­tion of heat pumped from the space to the exterior air. Less often, forced–air heating systems have cooling coils introduced into the airstream to provide a centrally cooled interior. A compressive cooling process is used, similar to that in a domestic refrigerator. A refrigerant, which is a liquid at room temperature, is pumped through a closed system of coiled copper tubes. An electric pump maintains a low pressure in the cooling coils, and the liquid refrig­erant passes through an expansion valve from a region of high pressure to the low–pressure coils. This change in pressure results in a phase change of the refrigerant; it turns from a liquid into a gas and absorbs heat in the process, just as water absorbs heat when it is boiled and converted into steam. The heat absorption of the liquid–to–gas transition cools air passing over the cooling coils. The cooled air is circulated through the building by the forced–air system. When the low–pressure gaseous refriger­ant leaves the cooling coils, it goes through the pump and is pressurized. The refrigerant travels through condensing coils, which are located outside the building; there the phase change is reversed as the gas turns to a high–pres­sure liquid and liberates heat to the exterior air passing over the condensing coils. The liquid refrigerant returns to the expansion valve to repeat the cooling cycle. The refrigeration machine is thus a "heat pump" that moves heat out of the building to the exterior atmosphere. Heat pumps can also be run in reverse in the winter months to pump heat from the outside air into the building interior; they work best in mild climates with fairly warm winter temperatures. The use of heat pumps in cold climates poses many difficult technological problems.

Interior atmospheres are also ventilated by operating windows, as well as by unintended leakage at all types of exterior openings. Bathrooms, kitchens, and laundries generate odours and heat and often have separate exhaust systems powered by electric fans that are operated inter­mittently as required. Residential atmosphere quality is also protected by the smoke detector, which sounds an alarm to warn of possible danger when smoke reaches even a very low level in living spaces.

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