Quote:
Originally Posted by 767Jockey
Is the heat pump that much more efficient than a gas furnace to put in a wacky system like this? I'm paying about $0.13 per KWH for electric, so the juice isn't super cheap down here.  |
If you haven't studied thermodynamics, you may have to take my word for this one. But yes, within a certain temperature range, a heat pump is more efficient and cost effective than a furnace. Here's my attempt at an explanation. Energy is energy whether it is in the form of watts of electricity, cubic feet of natural gas, or a volume of warm air flowing into your house. Any form of energy can be expressed in standard units such as BTUs. It turns out that if you burn a volume of natural gas containing 1,000 BTUs of energy, you'll get a volume of warm air containing about 1,000 BTUs of heat. (There is some loss of energy due to inefficiencies such as hot exhaust going up the flue.) But a heat pump is different. A heat pump uses a refrigeration cycle to move energy from one place to another. In its heating mode, the heat pump extracts heat energy from the outside air and carries that heat inside where it is used to heat the air blowing through your house. (Yes, even when it's cold outside there is enough heat energy in the outside air to take some to heat your house). Even with all the inefficiencies of operating pumps and moving heat over a distance, when the outside air temperature is above 35 degrees or so, it can transfer more heat energy to your house than it uses in electrical energy to do the job. For example, your system might use 50 BTUs of electical energy to transfer 100 BTUs of heat to your house. So the bottom line is that in the south where outside air temps don't stay too cold, a heat pump is usually more cost effective. But they don't work as well as the outside temperature gets colder.