Most air conditioners have their capacity rated in British thermal units (Btu). A Btu is the amount of heat necessary to raise the temperature of 1 pound (0.45 kilograms) of water one degree Fahrenheit (0.56 degrees Celsius). One Btu equals 1,055 joules. In heating and cooling terms, one 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 square meters) house might have a 5-ton (60,000-Btu) air conditioning system, implying that you might need perhaps 30 Btu per square foot. These are rough estimates. To size an air conditioner accurately for your specific application, you should contact an HVAC contractor. The energy efficiency rating (EER) of an air conditioner is its Btu rating over its wattage. As an 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 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 determine the payback period on the more expensive unit, you need to know approximately how many hours per year you will be operating the air conditioner and how much a kilowatt-hour (kWh) costs in your area. Assuming you plan to use the air conditioner six hours a day for four months of the year, at a cost of $0.10/kWh. house a c unit freezing upThe difference in energy consumption between the two units is 200 watts. ac split system for saleThis means that every five hours the less expensive unit will consume one additional kWh (or $0.10) more than the more expensive unit.air conditioning unit whole house

Let's do the math: With roughly 30 days in a month, you're operating the air conditioner: 4 months x 30 days per month x 6 hours per day = 720 hours [(720 hours x 200 watts) / (1000 watts/kilowatt)] x $0.10/kilowatt hours = $14.40 The more expensive air conditioning unit costs $100 more to purchase but less money to operate. In our example, it'll take seven years for the higher priced unit to break even.You are hereSupport » Product Support Frequently Asked Questions About Solar, Charging Systems and InvertersDaft Logic > Information > Appliance Power Consumption Turn that TV off if you're not watching it! How much electricity is it really wasting?, and would it not be better to switch off the 4 lights in the room? The best way to compare the cost of running different appliances is to look at their power consumption, which is measure of how much power they use in Watts. The following list points out typical values for the wattage of some devices you would find in your home so that you can compare them.

An important point is also to bear in mind the length of time for which the device will be used. For example an electric blanket may be used for 2 hours, but a hair drier for 5 minutes. Therefore the blanket uses 200W * 2 hours = 0.4kWh. The hair drier uses 2KW * 0.0833hours = 0.1666kWh. So using the blanket costs roughly 2.5 times as much as the hair drier. All values reported here are estimates, you should check the appliance labels or literature to find out the correct power consumption.What is the difference between an AC and a DC watt? When shopping for solar power systems and reviewing solar incentives from your state or your utility company, be sure you’re comparing apples to apples, and oranges to oranges. Or rather DC watts to DC watts (like in a battery) and AC watts to AC watts (like your appliances at home). The size of a solar power system is measured in watts. Some state incentives specify that they will reimburse a specific dollar amount per AC watt, while others specify a DC watt.

(Still others will award a solar power system owner for every kilowatt hour their system generates, among other methods.) As far as solar power system quotes go, you’re more likely to get a quote based on a DC measurement. In order to be accurate in your budgeting, it’s best to know the difference. If you take a solar power system with twelve 200-watt solar panels, your system size is 2,400 watts. But is that DC or AC watts? If you’re taking the manufacturer’s maximum power rating, or STC rating, it is a DC measurement. (STC stands for Standard Test Conditions.) Price quotes normally use the STC rating. There is also another DC measurement, the PTC rating, which is closer to a solar panel’s output in real world conditions. PTC refers to PVUSA Test Conditions, which were developed to test and compare PV systems as part of the PVUSA (Photovoltaics for Utility Scale Applications) project. PTC requires that a solar panel has 1,000 watts per square meter of solar irradiance, 20 degrees C air temperature, and a wind speed of 1 meter per second at 10 meters above ground level.

The California Energy Commission tests solar panels in the field using these conditions and lists their PTC ratings on a CEC approved list. The CEC is considered the authority on solar panel PTC ratings. While many solar panel spec sheets list the PTC as well as the STC, the CEC listing is the one to use in your calculations. So what is an AC watt? In a solar power system, the inverter is responsible for converting a DC electrical current into an AC electrical current, the type of electrical current that normal home appliances use. The AC wattage is figured when you take a solar panel’s listed PTC measurement and multiply it by the inverter efficiency, which is normally around 95 percent. A solar panel with a PTC rating of 180 watts, for example, would be sized at 171 AC watts (180 watts x 95%). A system with twelve of these panels would be sized at 2,052 AC watts (171 AC watts x 12). Here is CEC's list of inverters and their efficiencies. What is the difference between a watt, a kilowatt and a kilowatt hour (kWh)?

A watt is a unit of power that measures the rate of energy transfer or usage. A kilowatt is equal to 1,000 watts. A kilowatt hour is the amount of electricity used. To calculate the amount an appliance uses in kilowatt hours, take its wattage, multiply it by the number of hours you use it, and divide by 1,000. If you take a 100-watt light bulb and use it for 540 hours, the light bulb will use 54 kWh of electricity. Example of a Monthly Power Bill If you look at your power bill, you will see your monthly kilowatt hour usage. This is how much electricity you used for that month and were charged for. Normally your power company will bill you based on a rate per kWh. Sometimes this rate varies depending on the time of day or your usage. When shopping for solar power systems, it's useful to know what your kWh usage per month is. Wholesale Solar lists projected monthly kilowatt hours with each of their solar power systems whether they're grid-tied or off-grid systems. To get a better idea of what size of solar power system you're looking for, you can compare these with your power bill kWh usage.