Air Conditioners & Heat Pumps
Both air conditioners and heat pumps operate off of 100% electricity to heat/cool your home. These systems utilitze a liquid refrigerant to transport the heat between inside and outside AIR. The large condenser unit that you typically see outside is where this exchange takes place (seen in photo at right).
Dehumidification
When these systems are sized and installed properly, they function quite well as dehumidifiers (in A/C mode). When they are not sized/installed properly, you end up with high moisture levels inside the home. When units are not sized/designed correctly they often "short cycle," satisfying the thermometer before having a chance to condense any moisture from the air.
If using a heat pump, the proper size system should be selected based on its ability to handle the dehumidification requirements of your home. When the home's heating need is larger than its cooling need (common for our region), a "second-stage" of heating is needed. Two-staged heat pumps are ideal for this exact reason. A furnace can also be used to provide the additional heating needs, and is sometimes a necessity when heating requirements are high.
Heating Mode and The Need for "Back-up" Heat
Heat pumps are essentially air conditioners that can also run in reverse, bringing heat into the house in addition to being able to remove it. Because this type of system extracts heat from the outdoor air, it becomes more difficult to extract heat when the air becomes colder. As the outside air temperature drops, the amount of heat the system can extract from this air decreases. Because of this deminishing supply of heat, there must be some form of "backup" heat, to make up the difference between what the heat pump can produce and what your house actually needs to maintain a comfortable living environment.
There are essentially two types of this "back-up" heat.
- The standard type is electric resistance coils (think baseboard heaters). While this has a low initial cost, it is a very inefficient way to use electricity, which leads to high electric bills. By reducing the use of this form of back-up heat, the need for additional power plants will be reduced.
- Furnaces are the second type of "back-up" heat. Furnaces serve the same purpose as the electric strip heaters do - making up the difference between the heat pump capacity and the demand of the space being heated. Furnaces are a much more efficient way to provide this back up heat. These can be oil, propane, or natural gas. Out of these three fuel sources, the popane and natural gas furnaces are the most efficient (up to ~ 95%).
Designing with Heat Pumps
Special care and attention must be taken in the selection of heat pumps. There are a variety of factors that must be considered to ensure optimum performance. The size of the unit affects both the heating and cooling capability, the need for a back-up heat source, as well as the system's ability to dehumidify properly. Oversizing the system will make it difficult to maintain a dry living environment in the summer months, often leading to air-quality issues. If zoning is needed, we often recommend units that have 2-stage outdoor compressors and intellegent ECM blowers that allow greater control over airflow, allowing smaller zones to be created with more effective moisture management. Proper sizing, selection, and design is crucial to maximize the performance of your heat pump system.
