How do I select the right contractor? System sizing and proper installation are critical to energy efficiency and home comfort. It’s important to hire a qualified contractor who uses Manual J or an equivalent size calculation tool. If your contractor is certified by North American Technician Excellence (NATE), you know they’ve received special training about how to size and install your system. Note: NATE certification is not required for customers to receive rebates. Resources for finding a contractor: AC Check Trained Contractors Air Conditioning Contractors of America North American Technician Excellence (NATE) How are air conditioners typically sized to meet the cooling needs for my home? Your comfort while using air conditioning depends both on reducing air temperature and removing humidity. An air conditioner should ideally run for 20 minutes or more on each cycle to cool the indoor air and to reduce humidity. Oversized air conditioners run in short inefficient cycles.

They waste energy since they must run for a few minutes at the beginning of every cycle just to cool down the indoor coil and ducts. Only then can they can cool and de-humidify your home. That original cool-down energy is wasted after the air conditioner shuts off. What is meant by “BTU” and “Ton?” An air conditioner's ability to remove heat is expressed in BTUs (British Thermal Units) per hour,or "tons" of cooling. Each ton equals 12,000 BTUs per hour, and is equal to the energy contained in a ton of ice, a term left over from the days when buildings were cooled with ice. Your air conditioner should have a ton of cooling capacity for every 400 to 1,000 square feet of floor area, depending on your home's energy efficiency and your local climate. How does insulation affect my cooling needs? A poorly shaded home with little insulation and lots of air leaks might need a ton of air conditioning for every 400 square feet of floor area. A well insulated and well-shaded home with few air leaks might only need one ton per 1000 square feet.

Contractors size air conditioning systems using computer programs or extensive hand calculations. To ensure correct sizing, ask your contractor to show you the written calculations for your home. Then have them install the smallest size air conditioner capable of cooling your home. What is the difference between EER and SEER? EER (energy efficiency ratio) is a measure of how efficiently a cooling system will operate when the outdoor temperature is at a specific level (usually 95° F). A higher EER means the system is more efficient. You can calculate kilowatts if you know the EER and the size, in tons. EER = BTUs of Cooling @ 95F / Watts used @ 95F In the case of a 10 EER, 2 ton air conditioner: 10 EER = 24,000 BTUs Out / 2,400 Watts In For the same size unit, but rated at 12 EER: 2 EER = 24,000 BTUs Out / 2,000 Watts In or 20% more efficient. If you want to calculate kilowatt-hours, just multiply the "Watts In" by the number of hours that the air conditioner is running.

SEER (seasonal energy efficiency ratio) is a measure of efficiency over an entire cooling season, as opposed to a single outdoor temperature. Residential units are almost always rated in SEER. SEER came into use as a more practical measure, since the temperature outside is not always 95º F. Also, the denominator is in watt-hours, not in watts as is the case for EER. how fresh air handling unit worksThe same relationship holds ... a higher SEER means the system is more efficient. air conditioning units whole houseSEER is the total amount of cooling the air conditioner will provide over the entire cooling season divided by the total number of watt-hours it will consume or:ac window unit target SEER = Seasonal BTUs of cooling / Seasonal watt- hours used

What is the importance of EER? There are many goals and benefits of utility sponsored Efficiency Programs. Among these is education for the purpose of using energy wisely. From this a rating system to establish standards for energy consumption has been developed. One way to measure energy consumption is Seasonal Energy Efficiency Ratio (SEER). SEER is a measure of efficiency over an entire cooling season. SEER ratings are useful in determining the amount of energy used and the amount of energy saved. Often, the unit of measure associated with SEER is kilowatt-hours (kwh). A kilowatt is 1000 watts used for 1 hour. SEER = Seasonal BTUs of cooling / Seasonal watt- hours used. There is more to energy consumption than kwh. Another measure of energy (and thus energy efficiency) is demand. Demand is the maximum amount of electricity used by an air conditioning system. This usually occurs at start up. The unit of measure associated with demand (or peak) is Energy Efficiency Ratio or EER.

EER = BTUs of Cooling @ 95F / Watts used @ 95F. Almost all air conditioning units are tested under the same controlled and specific laboratory conditions to determine the EER rating. Your local sponsors, and the country as a whole, are concerned about using energy efficiently. Efficient usage occurs both in the seasonal and peak arenas. Many advocacy partners in the industry recognize SEER alone does not address demand savings. Use of EER as an industry standard is in an attempt to for continued improvement in demand performance.It seems like Tesla might be making a battery for your house. Would that be cool? But why would you need a house battery? I can think of a couple of uses: For an off-grid house you might like to power it with solar or wind power. Unfortunately, neither of these two sources provide constant energy. If you could store the energy in a battery, you could use this during the night or calm weather. Many people keep a gasoline powered generator for their house.

I have one that I don’t use too often, but it’s awesome when you need it. What if you had a battery that you could use for your house in times of power outages? That would be cool. It seems like the power company would like everyone to have a battery. With a house battery, you could reduce power spikes on the grid. When you turn your air conditioner on, it draws a large current for a short period of time(here’s an explanation of why the current spikes). With a battery this current demand could be leveled out (I guess). But that’s not why you are here, is it? You want to know how big of a battery you would need. We need some starting values. First, how long do you want to run your house on a battery? I think Elon Musk (from Tesla) said one week. The next big thing is the power usage. I think a fair assumption is a constant 2000 Watt power usage. Clearly a house would need more than 2000 watts at some point in the day. However, at night you wouldn’t need much power such that the average for the day could be 2000 watts.

If you don’t like that value, you can put your own numbers into the calculations. If I know the power and the time, I can use the definition of power to calculate the energy stored in the battery. Having the power in Watts is fine (since a watt is a Joule per second) but I need the time in seconds. Now I can calculate the stored energy in the battery.But what the heck is a Joule? Sure, it’s a unit of energy but is that a large amount? Here’s a simple experiment you can do yourself. Take a textbook and put it on the floor. Now pick it up and put it on a table. In order to lift the book, you need energy (to change its gravitational potential energy). A book is about 1 kg and you lifted it about 1 meter. That makes a change in energy of about 10 Joules (don’t forget the gravitational field is 9.8 N/kg). So now you know about Joules. Now for the battery size. The dimensions of the battery will depend on the type of battery. The current Tesla vehicles use a lithium ion battery.

According to Wikipedia, the lithium ion battery has an energy density from 0.9 – 2.23 MJ/L (mega Joule per liter). I would imagine that Tesla would only use THE BEST BATTERIES! That would put its energy density at 2.3 x 109 Joules per cubic meter. If I call the energy density σ, then I can find the battery volume: Putting in values for the energy density and the battery energy: So just half a cubic meter. That’s not too bad. If you want to put this inside your house, you could make it as tall as a wall (let’s say 2.5 meters). Now from a design view maybe a battery should be just 5 cm thick. This means that it would have to be about 4 meters wide. Ok – that wouldn’t work. If increase the thickness to 10 cm, it would just be 2 meters wide. Of course, this only really works because of the high energy density for a lithium ion battery. If you used an akaline battery (like AAs) it has a lower energy density at around 1.8 MJ/L such that it would be slightly larger house battery (but not rechargable).

You can look at the Wikipedia page on energy density to get an estimate for house batteries of different materials. Just for fun, what if you made a penny battery (from copper-zinc pennies and acid)? How big of a battery would you need in that case? Here is your answer. This is just a perfect story for homework. It won’t be too difficult, so don’t delay and start soon. What if you wanted to run your house on AA Cell batteries? From my previous investigation, I found that a AA battery has about 10,000 Joules of stored energy. How many AA batteries would you need and how much space would it take up? What if you wanted to run your house on a nuclear power plant that used Thorium? How much Thorium would you need? Use the energy density from Wikipedia. According to this news, Apple will build a 130 MegaWatt solar farm to use for its stores and stuff. What if you wanted to run your house completely off grid with solar panels and batteries. How big would the solar panels be?