Heat Pumps are Hot Right Now
And cool, too!
In the world of climate action, heat pumps are a hot topic. Here’s why:
- Heating, ventilation, and air conditioning (HVAC) is the most energy-intensive element of our day-to-day lives, and
- The production of energy that powers homes and businesses is the #1 source of South Bend’s climate pollution.
What is a Heat Pump?
Heat pumps are mechanical heating and cooling systems that use a bidirectional, “loop” system to condense and transfer heat. Gas furnaces, by comparison, use combustion of fossil fuels to generate heat to warm the air. Heat transfer is more efficient than heat generation.
It’s all in the name:
- Air-to-Air
- Geothermal or “Ground-Source”
- Air-to-Water
1. Air-to-Air
Heat pumps are not exactly a new or untested technology. They have been around for a while! But, newly, there is increased adoption of air-to-air heat pump systems that prove to be efficient even at low temperatures.
Think of air-to-air heat pumps as a traditional AC unit with a reversing valve. They condense and transfer (even very-low-temperature) heat in and out of a building. Air-to-air systems are less efficient when outdoor temperatures are extremely low, and some building owners choose to have back-up gas heating or “hybrid” systems for extreme cold.
2. Geothermal or “Ground-Source”
Geothermal or “ground-source” heat pumps transfer heat in a loop system in the ground or water source (e.g., a pond or well). The steady 55-degree temperature of the earth and deep water is like a thermal battery for heat transfer. Underground temperatures remain steady despite extreme outdoor temperature fluctuations.
Hot tip! Good insulation improves efficiency.
Upfront costs of geothermal can be prohibitive, but long-term energy savings pay for a project over time. Federal rebates and tax incentives for solar and heat pump systems may lower up-front costs of investment and reduce payback periods for clean-energy projects, including geothermal.
Ross Reserve: a Midwestern Heat Pump Success Story!
Purdue University’s Ross Reserve building project is single-family housing size (~1200 ft^2). With 28 solar panels, the building produces surplus energy. It is a certified “Living Building” (one of two in Indiana) made of natural and local materials. It uses a groundwater-driven heat-pump system to power water-to-water heat transfer in a radiant floor. The hot water tank has a desuperheater that transfers “waste” heat into hot water for showers and dishes in the summertime, while also providing AC.
Hot tip! Water is a thermal battery; Water tanks store heat at useful temperatures.
3. Air-to-Water
Air-to-water heat pump systems are a 3-in-1: they heat, cool, and provide hot water — all in one fairly simple system design. Air-to-water heat pumps use water to store and transfer low-temperature heat from the air and deliver it through pipes at useful temperatures in a hot water system.
Air-to-water heat pump technology is taking off in places with more moderate temperatures, like California, and being successfully implemented in cold temperatures climates of Europe. Unfortunately, some of the latest and greatest technology on this front has yet to reach the Midwest.
Hot tip! Right-sizing your system is key.
Right-Sizing
To maximize efficiency, heat pump systems must be right-sized to a building. Undersized systems can increase a homeowner’s reliance on supplemental electric heat and lead to early equipment failure. Oversized systems are more expensive to install and “short-cycle” (turn on and off frequently) which leads to irregular distribution of heat throughout a space and also reduces the lifespan of the equipment. Right-sizing your system requires calculating many factors including home size, insulation, number of windows, geography, duct leakage, and orientation to the sun.
Mike Keen’s Hot Tips for Heat Pumps
Mike Keen, Managing Partner of Hometowne Development LLC, is a community organizer and leader of fair, equitable, and environmentally friendly small-scale neighborhood redevelopment in South Bend. He owns an air-to-air heat pump system, installed last year (2023).
- Aim for a stable temperature
You do not use the thermostat in the same way. That is, turn it way down in winter overnight to save energy. That is because it does not heat up the house quickly like a gas fired furnace. So we typically just set it so that it goes down 4 degrees over night. It is most efficient when it gets house to the temperature you want and then uses the pump to maintain it. - Enjoy the low-humidity AC
When we had to use it for AC in summer it was also terrific at keeping humidity down. - Heat pumps are efficient & comfortable
The cost to heat and cool our house did not really change much. However it is a much more comfortable system. House stays a constant temperature.
Could a water-to-water, water-to-air, or air-to-water heat pump system work for your building? If you are considering it as an option, please let us at the Office of Sustainability know! We would be excited to learn with you.
