Fossil Fuel with Heat Pump

History:

Before the popularity of heat pumps the primary source of heat with forced air was oil and natural gas with some propane. Early heat pump systems fell into unpopularity because of poor performance in cold weather and the price of fossil fuel was low and they were used as a system of last resort.

As heat pump system performance improved they became more popular but only when fossil fuel was unavailable or inconvenient. However heat pumps proved to be economical as a supplement to oil systems and in some locations natural gas by supplying slightly better economics in mild weather where heating is still required and a heat pump provided cooling in the summer.

In the late 1990s The price of natural gas hit some very high peaks ending the traditional price of 40 cents a therm. in the mid 2000s the price of fuel oil hit highs of 3 times what it has been on the late to mid 90s and remains very high today and world conflicts continue to keep oil prices high.

Today high prices of all fossil fuels and large improvements in heat pump efficiencies over the years have make the economics of a heat pump combined with fossil fuel not just attractive economically but necessary. Even with increases in electric rates in most parts of the United States a heat pump will usually win out over oil and in many cases natural gas by providing 2-4 time the amount of energy in heat that it consumes. The price of propane usually follows the price of oil.

The heat pump and fossil fuel system usually consists of a gas or oil furnace with a refrigerant coil on the discharge or in some cases on the inlet and a heat pump for the outdoor unit. The heat pump is usually sized for Summer cooling with the idea that in Winter any heating deficiencies can be made up with fossil fuel. The advent of 2 stage heat pumps will make it possible to increase the size of the heat pump almost to the point that the heat pump can provide most of the Winter heating needs reducing or eliminating fossil fuel use but preserving it for extreme temperature lows.

The controls for a heat pump with fossil fuel are wide and varied depending on what controls are used. The basic theory of operation is that below a certain outside temperature the operation will switch from heat pump operation to fossil fuel, in the past this was done in the name of comfort but today it needs to be done based on economic balance point (see definitions).