What is a Heat Pump?

This summer the Green Committee completed the installation of two solar arrays (solar panels), one on the Town Hall Annex and another on the DPW Garage. The arrays are performing extremely well and are currently producing more power than expected. Each array is producing more than 1,750 kWh (kilo Watt hours) per month. The current high performance is mostly due to the sunny weather conditions, but as we get into the cloudy fall and winter months, electric production is expected to decrease. However, the anticipated annual electric production is expected to be at least 10,000 kWh per array.

Sandisfield PV Production July 2022

Figure 1.

The next project the Green Committee will be working on is to install a heat pump in the Town Hall Annex and possibly the DPW garage. It was always planned to pair the Town Hall Annex solar array with a heat pump to reduce the town’s energy usage. The heat pump in the Town Hall Annex is expected to use 10,000 kWh/year. This will use most of the electric energy produced by the Town Hall Annex solar array, but since the heat pump will be heating the building, this will greatly reduce the oil usage for the boiler to almost zero. Not only will this system reduce town expenses, it will also reduce our carbon footprint.

It still has to be decided if it worth installing a heat pump for the new DPW garage. The new building is the most energy efficient building the town now owns, so the Green Committee still has to decide if it’s worth reducing propane usage or do we just return the electric energy credit to the town’s budget.

Four questions generally come up about heat pumps. 

  • What is a heat pump?
  • How does it work?
  • How much does it cost?
  • How efficient are they in very cold weather?

The Thermodynamic Cycle

A heat pump basically works like an air conditioner, but unlike an air conditioner that is used only for cooling, a heat pump can also be used to heat your home. Before describing the heat pump, it’s necessary to understand the Thermodynamic Cycle. Figure 2 shows the four basic components in an air conditioner:

  1. Compressor,
  2. Condenser,
  3. Expansion valve.
  4. Evaporator.

These four components are connected through internal plumbing to transfer liquid refrigerant to each component to transfer heat and cooling. The system also incorporates a fan for greater efficiency in transferring energy. When you turn on an air conditioner, it operates as follows.

Air conditioner Schematic

Figure 2.

  1. The compressor turns on and compresses the refrigerant in the condenser.  Any liquid or gas that is compressed, will create heat.
  2. As the heated refrigerant passes through the condenser, the refrigerant begins to cool as air passes over cooling fins in the condenser, aided by a cooling fan. This process transfers heat to the outside air.
  3. The refrigerant then passes through the expansion valve. Any gas or liquid released under pressure will cool as it expands.
  4. The cooled refrigerant then passes through the evaporator. With the aid of a fan, air passes over the evaporator which you will feel as cool air.

A heat pump works basically the same way, but it gets slightly more complicated because it includes additional components. One major component is called a Reversing Valve. Other components include two Expansion Valves modified with a Bypass Valve.  Now instead of just cooling, a heat pump can supply both interior heating and cooling air. This process is controlled by the reversing valve and the modified expansion valves, depending on whether hot or cold air is called for. Figure 3 is a basic a schematic of a heat pump but there are many excellent videos online explaining heat pump operation. Heat Pumps Explained.  

Heat Pump Schematic

Figure 3.

Heat Pump prices vary widely depending on installation. An excerpt from BobVila.com states, "In moderate climates, heat pumps can be more energy-efficient than furnaces. They typically range in price from $4,133 to $7,294, with a national average of about $5,696." However, the first quote the Green Committee received for the Town Hall Annex is $60,000, but the Town Hall Annex is a large commercial installation.

Prices would vary depending on the complexity of the installation, which would include the piping   into the house to a heat-exchanger into existing ducting. Another option is to install mini-splits. What is a Mini-split? The mini-split is a heat-exchanger that delivers either hot or cold air into your house.  As I have said, there are many types of installation, but let’s look at the mini-split.

Mini Split Schematic

Figure 4.

Mini-splits are small heat exchangers that can be installed throughout your house, and you can create multi-zones. Each room can have its own mini-split and thermostat to control heating or cooling. Depending on the complexity of your installation, this would determine the price.

How Efficient are Heat Pumps?

There is conflicting information on the efficiency of heat pumps. Eversource reports that “Heat pumps can be up to 400% efficient - much more than heating with oil, propane or electric resistance baseboards. This can lead to savings on your energy bills.” However, www.estesair.com, a furnace provider in Atlanta reports, “Heat pumps do not operate as efficiently when temperatures drop to between 25 and 40 degrees Fahrenheit. A heat pump works best when the temperature is above 40.” It's possible that Estesair is referring to older less efficient systems. Newer heat pumps use a different refrigerant (R410a) and would be more efficient and heat pumps can provide heat even if the outside air temperature is -10 degrees Fahrenheit. We hope we have provided some answers here but for an accurate cost of heat pump installation and operation, it would be best to contact a local plumbing and heating company for a quote.