Heat Pumps 101

Most of the heat pumps now in existence are at a critical stage in their life. Generally, the average life span of those heat pumps is about 10 to 15 years and they will need replacing very soon. What do you do if you own one? First, it's important to understand some of the differences between various types of heat pumps and air conditioning units.

Heat pumps are designed to warm in winter and cool in summer. In winter, they only warm to a certain extent and are backed up, for example, by a forced air gas furnace. Many of the heat pumps in use today are fueled by electricity and have an efficiency rating about 3 times higher than natural gas. Consequently, people have chosen to disable the unit for warming and use it solely for cooling.

One rating commonly used is called the COP (Co-efficient of Performance). This is similar to a miles per gallon type rating. The higher the rating the higher the efficiency is. For example, here are some furnace ratings: Electric (1.0), Oil (1.75-2.0), Propane (1.6-2.0), and, High-efficiency Natural Gas (2.0-2.3)

There are three basic types of heat pumps -- Air Source, Water Source, and, Ground Source.

Air Source -- Most of the heat pumps in use today are Air Source. As its name implies the outside air is utilized to draw heat from during the heating season and ejects heat outside during the cooling season. There are two types of Air Source heat pumps.

a) Air to Air -- takes heat from outside air and transfers to the interior or exterior of the home depending on the season. This is the most common of all heat pump types.

b) Air to Water -- takes heat from outside air and transfers it to water in a hydronic heat distribution system. In cooling season it takes heat from hydronic distribution system and ejects it outside the home.

Although conceptually, or theoretically, Air Source heat pumps are a great idea the operating costs are very high as it is fueled by electricity for cooling and heating (in temperatures above freezing). They are largely thought to be gimmicky when compared to the efficiency of other types of cooling systems.

With Air Source heat pumps the heat exchanger is located inside the house with the compressor located outside the house.

Costs about $3 - 5,000, models -- forced-air, advantages -- least costly to purchase, disadvantages -- costly to operate, electric heat, COP -- 1.0-1.6 @ 0OC, 3.0 @ 20OC

Water Source -- This is referred to as an "open" system as the water is drawn up through a well directly to a heat exchanger where the heat is obtained. The water is then discharged back to an above ground body of water or to a separate well. It uses water as it source of heat in the winter and water as a method of cooling the heat removed from a house in the summer.

These units can be designed to have either a heating only, heating with passive cooling or heating with active cooling. The heat pump is typically located within the house.

Tip: When considering a central air conditioning unit, over a heat pump, a Water Source heat pump can be a better choice in certain circumstances.

Costs about $6,500+, models -- forced-air or hydronic, advantages -- highest efficiency, disadvantages -- requires more maintenance, COP -- 3.2-4.2

Ground Source -- This is referred to as a "closed-loop" system. It collects heat from a continuous loop of piping buried in the ground in winter. In summer, the pipes in the ground absorb heat thereby acting as cooling system.

These units can be designed to have either heating only, heating with passive cooling, or, heating with active cooling. The heat pump is typically located within the house.

Costs about $12 - 15,000, models -- forced-air or hydronic, advantages -- dependable, disadvantages -- costly to install, landscape concerns, COP -- 2.6 - 3.4

What's New In Heat Pumps? -- Traditionally, the most common system is an Air to Air heat pump powered by electricity. Now, YORK has come out with a 5 horsepower, one cylinder, glycol cooled, Briggs & Stratton motor (looks like those you see on a lawn mower) that is powered with cheaper natural gas for fuel. The result is that you can save about 50% over electric heat pumps.

Back