Heat Pumps: What’s The Big Mystery?
Most people, have heard of a heat pump - but few of us REALLY understand how they operate. In this brief article let us provide some simple explanations and illustrations of the technological principles common to most heat pumps.
First of all: The name - heat pump. Why are these things called a heat pump? What are they pumping anyway? The word ‘pump’ suggests that heat pumps are moving something, and indeed they are: heat, or more accurately, heat energy. Here’s an illustration of heat ‘moving.’ Go and get a cup of coffee from your favorite coffee shop. It’s piping hot when you get it (hopefully). But let it sit 15 or 20 minutes - then take a sip. What has happened? It ‘cooled off,’ right? Well, what really happened? Actually the heat energy present in the hot liquid escaped and was transferred into the air surrounding the cup. Heat was ‘moved’ from one location to another. Simple, huh?
You might not realize it, but even on the coldest day outside, the air contains some heat energy. The same is true for the ground beneath our feet: it has the capacity to store, or hold, heat energy. Heat pumps simply move, or ‘pump’ heat energy from one place to another. When you use a heat pump to heat or cool a room, you are making use of this basic fact of physics.
So let’s see a heat pump at work: you have a heat pump installed. It’s summertime, and your room is hot. A heat pump will circulate the air in the room, draw off some of the heat energy and transfer that heat energy outside. Because heat energy has been taken out from the room, you feel cooler.
What do you do in the winter? Simply reverse the whole process: use your heat pump to move heat energy from the outside to your rooms inside (even when it’s cold outside there’s heat energy there, remember?). You will feel warmer in that room as a result.
It is very important to remember that heat pumps do not actually burn fuel to add heat to any room - they simply move it from another location. This means that heat pumps are not furnaces - furnaces burn fuels, heat pumps do not. A heat pump is an energy-transferor, not a producer of energy.
Some heat pumps are called air-source heat pumps, so called because they use the air (surrounding the unit or from a separate unit outdoors) as their source for heating and cooling.
Other types of heat pumps include Geothermal heat pumps. These units use the ground - they draw heat from it to warm, and expel heat into it to cool. They make use of a complex system of coils that are buried into the ground. What makes it possible for these units to work is that below a certain depth, the temperature of the ground actually does not change very much from season-to-season.
Article Source: http://www.energyefficienthomearticles.com
I am building a modular log home (Blue Ridge Log Cabins)in Rutherfordton, NC (Blue Ridge foothills). I need advice on HVAC system using an electric heat pump.
The house footprint is 27′ x 33′ with finished and fully insulated Superior Walls walk-out basement; 890 sq.ft. of space on main floor (with about half of it open to the roof); 450 sq.ft. on upper floor (guest room & bath). All of this space is to be heated and cooled.
Roof is 12/12 pitch; R-38 insulation; dark green shingles. Roofed porches East & West along full length of the main floor. Construction is 6″ x 8″ milled logs (gasketed tongue and grove). Double-glazed windows and doors.
The builder’s present recommendation is for an EnergyStar heat pump, 16-17 SEER, 9.2-9.8 HSPF; variable speed air handler; zoned for basement thermostat separate from main floor and upper floor; electric supplemental heat.
Climate: average 122 days per year above 75F., average 91 days per year below 40F., average high 83F., average low 36F. There are about 80 days per year during December, January and February when the minimum temperature is below 28F.
I understand that the efficiency of heat pumps below 28F is poor. I take that to mean I will be using supplemental heat for more than 3 months per year.
Questions:
How much tonnage do I need?
Is the recommended system appropriate?
Can the cold-weather performance be improved by locating the outdoor coils in a sheltered area or enclosure that can be heated by passive solar technology or heat recovered from indoor appliances, etc.?
Can the hot-weather performance be improved by shading and ventilating the same area while diverting the recovered heat from indoor appliances?
If the above modifications will work, what are the downsides?
Comments from contractors, engineers, architects welcomed!