For Seattle-area residents looking to enhance their home’s efficiency and live greener lifestyles, one of the first places to look is home heating and cooling systems. Traditional HVAC systems account for an estimated 50% of your energy bill and operate at between 70 and 100% efficiency. Modern heat pumps, on the other hand, operate at about 300% efficiency.
What are Heat Pumps?
Heat pumps are heat engines that warm your home not by burning fuel, but by moving heat from one location to another. They need electricity to operate motors that compress a refrigerant, which causes it to heat up, then sends the hot refrigerant into your house. A fan blows air across a coil carrying the hot refrigerant (like the radiator on your car) to pull the heat out and spread it around your house. The refrigerant that has been cooled by the fan is then allowed to expand, which gets it very very cold. Then it is exposed to the outdoors, where it is warmed up, even if it’s 0 degrees outside, 0 is warmer that the expanded refrigerant, and the cycle repeats. The heat pump is moving heat out of the outdoors, into your house. Your refrigerator is a heat pump as well. It’s pulling heat out of the interior of the fridge and expelling it into your house using the same compression and decompression principle as the heat pump. Devices like these - refrigerators, air conditioners, and heat pumps - are collectively referred to as "heat engines."
Heat pumps come in different embodiments, but in NW homes, the most common types are ductless and ducted split systems. They are referred to as "split" because they have two parts, one outdoors and one in. The compressor goes outside and is simply called the outdoor unit. The indoor unit is just a fan and a heat exchanger. In the ductless embodiment, the indoor unit is located where the heat is delivered, the living room for example. In the ducted systems, the indoor unit goes where a traditional furnace would go, and is connect to the ducting. The fan blows the heated air through the ducts to deliver heat to the rooms.
In summer, a valve switches the direction of refrigerant flow and the heat engine acts to cool your home – it’s an air conditioner.
One of the main benefits of installing modern heat pumps is that they can be used to condition areas of the home that aren’t outfitted with ductwork. This is the perfect solution for rooms that have historically been difficult to heat or have simply been neglected in the past. Many homeowners augment their existing heating and cooling systems with heat pumps, which is an excellent way to save money while still utilizing the equipment you have installed in your home.
A few key facts about heat pumps:
- Since they pull heat from the outdoors, the colder it is outside, the less heat there is available to extract, so their performance drops off.
- Modern heat pumps can continue to pull heat from the atmosphere when it’s zero degrees out, but maybe not enough heat to keep you comfortable.
- Heat strip back up can be installed on ducted systems and make up for heat pump performance drop off on cold days
- Heat strip back up is installed sometimes even when the equipment is sized for the cold days to avoid cool air from being distributed during defrost cycles, where the outdoor coils are warmed to take the frost off of them.
- Modern heat pumps are inverter driven which allows for variable speed operation. In variable speed mode, the system works hard to get the house to the thermostat set point, then goes into cruise control which is highly efficient, very comfortable, and quiet.
- Ducts can reduce your heating efficiency by as much as 35% if they are located in unheated areas like under your home or in the attic, and not well sealed or insulated.
- Ducted heat pumps typically only have one thermostat. If it’s cold, you heat the whole house.
- Ductless heat pumps are zoned. If you install three indoor units, for example, you will have three thermostats and can heat only the areas of the home you want to.
- An important qualifier about the ductless heat pumps is that while they do operate as heating systems in winter and cooling systems in summer, it’s the outdoor unit that does the converting from heater to cooler. Since there is only one outdoor unit, you can’t have one indoor unit proving heat while another is cooling. They are all cooling or all heating.
- Many people don’t like the looks of the ductless indoor units. The manufacturers are trying to make them sleeker and cooler looking, but they are still big appliances that have to be mounted to your walls. Researchers took that on and found that people that took the plunge against their aesthetic judgment got comfortable within days of installation.
- Manufacturers have created some optional packages for the indoor units that are not so obvious visually. We do install them. Two caveats: they are considerably more expensive and they don’t work as well. But sometimes they are what’s called for.
At HomeRx we believe that heat pumps are the prescription that many Puget Sound-area homeowners need to make their homes more comfortable and to reduce the amount of money spent each year on heating and cooling.