BTU and EER

Most air conditioners have their capacity rated in British thermal units (BTU). Generally speaking, a BTU is the amount of heat required to raise the temperature of one pound (0.45 kg) of water 1 degree Fahrenheit (0.56 degrees Celsius). Specifically, 1 BTU equals 1,055 joules. In heating and cooling terms, 1 "ton" equals 12,000 BTU.

A typical window air conditioner might be rated at 10,000 BTU. For comparison, a typical 2,000-square-foot (185.8 m²) house might have a 5-ton (60,000-BTU) air conditioning system, implying that you might need perhaps 30 BTU per square foot. (Keep in mind that these are rough estimates. To size an air conditioner for your specific needs, contact an HVAC contractor.)

The energy efficiency rating (EER) of an air conditioner is its BTU rating over its wattage. For example, if a 10,000-BTU air conditioner consumes 1,200 watts, its EER is 8.3 (10,000 BTU/1,200 watts). Obviously, you would like the EER to be as high as possible, but normally a higher EER is accompanied by a higher price.

Let's say that you have a choice between two 10,000-BTU units. One has an EER of 8.3 and consumes 1,200 watts, and the other has an EER of 10 and consumes 1,000 watts. Let's also say that the price difference is $100. To understand what the payback period is on the more expensive unit, you need to know approximately how many hours per year you will be operating the unit and How much a kilowatt-hour (kWh) costs in your area

Let's say that you plan to use the air conditioner in the summer (four months a year) and it will be operating about six hours a day. Let's also imagine that the cost in your area is $0.10/kWh. The difference in energy consumption between the two units is 200 watts, which means that every five hours the less expensive unit will consume 1 additional kWh (and therefore $0.10 more) than the more expensive unit.

Assuming that there are 30 days in a month, you find that during the summer you're operating the air conditioner:

4 mo. x 30 days/mo. x 6 hr/day = 720 hours

[(720 hrs x 200 watts) / (1000 watts/kW)] x $0.10/kWh = $14.40

The more expensive unit costs $100 more, which means that it will take about seven years for the more expensive unit to break even.

See Climate Magic for a great explanation of seasonal energy efficiency rating (SEER).

In the next section, we'll look at cutting these costs with some new, energy-efficient cooling systems.

No Refrigerator Without Electricity - New Idea

Gas and Propane Refrigerators

If you own an RV or use a refrigerator where electricity is not available, chances are you have a gas- or propane-powered refrigerator.

These refrigerators are interesting because they have no moving parts and use gas or propane as their primary source of energy. Also, they use heat, in the form of burning propane, to produce the cold inside the refrigerator.

A gas refrigerator uses ammonia as the coolant, and it uses water, ammonia and hydrogen gas to create a continuous cycle for the ammonia. The refrigerator has five main parts:

* Generator - generates ammonia gas

* Separator - separates ammonia gas from water

* Condenser - where hot ammonia gas is cooled and condensed to create liquid ammonia

* Evaporator - where liquid ammonia evaporates to create cold temperatures inside the refrigerator

* Absorber - absorbs the ammonia gas in water

The cycle works like this:

1. Heat is applied to the generator. The heat comes from burning something like gas, propane or kerosene.

2. In the generator is a solution of ammonia and water. The heat raises the temperature of the solution to the boiling point of the ammonia.

3. The boiling solution flows to the separator. In the separator, the water separates from the ammonia gas.

4. The ammonia gas flows upward to the condenser. The condenser is composed of metal coils and fins that allow the ammonia gas to dissipate its heat and condense into a liquid.

5. The liquid ammonia makes its way to the evaporator, where it mixes with hydrogen gas and evaporates, producing cold temperatures inside the refrigerator.

6. The ammonia and hydrogen gases flow to the absorber. Here, the water that has collected in the separator is mixed with the ammonia and hydrogen gases.

7. The ammonia forms a solution with the water and releases the hydrogen gas, which flows back to the evaporator.

The ammonia-and-water solution flows toward the generator to repeat the cycle.

Various Definitions Regarding Refrigerators

Absorption		A process in which energy (heat) is taken up by a liquid or solid.
Compressor		This is a pump which compresses refrigerant gas, and consequently heats the gas.
Condensation		A change of state from gas or vapour to liquid.
Evaporation		A change of state from solid or liquid to gas or vapour. It occurs when some molecules of a liquid have enough energy to escape into the gas phase and this has an overall cooling effect on the liquid.
Expansion		The increase of volume of a sample of substance.
Intermediate temperature		A temperature somewhere between hot and cold.
Refrigerant		A chemical substance used as a fluid in a refrigeration system. There are many different types of fluid used, depending on the system design. Most commonly used are hydrofluorocarbons (HFCs) and hydrocarbons (HCs).
Refrigeration		This is the transfer of heat from a substance to be cooled to somewhere else. Heat flows naturally from a warm substance to a colder one eg fish can be cooled by surrounding it with packing ice.
Restrictor		Something that restricts the flow of a gas or liquid.
Sublimation		This is when a solid turns to vapour without going through the liquid phase. For example, you can see solid carbon dioxide (CO2) turning to vapour when it melts without producing a liquid (dry ice).
Thermal Insulation		A means of preventing or reducing the transfer of thermal energy (heat). Good insulators are foam, wool, and vacuums.
Vapour		A substance in a gas state that has reached a temperature at which it could become a liquid just by the application of pressure. It is usually still in contact with the liquid from which it was formed.
Ventilation		The addition of fresh air.