Why I’m Excited about Heat Pumps , and Why You Should Be Too

November 21, 2018Sustainability

Joel Zook, Energy Planner

In the clean energy line-up, Solar is the MVP. We get it. Solar is shiny and new, it slashes your electric bill, you’re creating your very own clean energy – what could be better? But if you dig down to why people install solar there are often two main reasons: it makes sense financially, and it’s going to help reduce their impact. I’m here to introduce you to a workhorse on the clean energy team that doesn’t get a lot of attention but can make a big impact as well, both for your budget and for the environment.

Heat pumps work by transferring heat from one place to another. Although there are some key differences between them, both refrigerators and air conditioners are heat pumps and work on the same basic principal. They remove heat from the air and dump it elsewhere. A fridge works by removing heat from the air inside the fridge and dumps it into your kitchen. An air conditioner removes heat from the air in your house and dumps it outside. Heat pumps can also be used for heating. A heat pump water heater takes heat from the air in your house and “dumps” it into water to warm it.

Rocky Mountain Institute released The Economics of Electrifying Buildings this summer outlining the cost and environmental benefits from using electric heat pumps to replace direct fossil fuel use in buildings.

Here’s the case they make in short:

  • The electric grid is getting cleaner as coal plants are retired and more clean energy comes online. (Power generation accounts for about a third of the US’s greenhouse gas emissions. Transportation has recently overtaken power generation as the US’s largest sector of greenhouse gas emissions. This is why we need to electrify transportation, but that is another story).
  • Buildings across America burn fuels for space and water heating. This direct combustion within buildings accounts for about 10% of US greenhouse gas emissions.
  • If we want to get to 100% renewable energy we need a clean, green way to provide space and water heating.
  • Heat pumps, powered by clean electricity can do this. In fact, it is already economical AND a net benefit to the environment to make the switch in many locations
  • We need to start the switch now to avoid building out infrastructure that “bakes in” fossil fuel usage.

It is cost-effective now to build new, all-electric homes with no combustion appliances. It is cost effective now for LP customers to upgrade to heat pump water heaters and air-source heat pumps – when replacing an old or failing water heater or air conditioner.

I’ll use my home as a real-life example of how these economics and environmental benefits play out:

I have an older, standard efficiency gas water heater that vents up my chimney. Gas water heaters are not a very efficient technology. The older units are basically a large gas burner sitting underneath a somewhat insulated tank. Not all of the gas burned is converted into hot water, some goes up the chimney. Some heat is lost from the hot tank and warms up my house. Some gas is used just to keep the pilot light running 24/7. Altogether, my water heater is 60% efficient at best. For every dollar I spend on natural gas, only 60 cents is put to good use.

I use 240 therms per year for hot water, which costs about $150. If I were heating with LP, the same amount of energy would cost $340 per year. You can see already that LP users pay significantly more for their energy than natural gas customers.

Heat pump water heater efficiency is measured by how much heat they can create with a given unit of electricity. For every kWh used, they can provide the equivalent of 2 to 3.5 kWh of heat. I estimate a heat pump water heater with an EF of 3.5 could provide my family with hot water and use 1,205 kWh per year. This provides hot water at a similar price to a standard efficiency natural gas water heater and would save an LP customer about $160 per year. Neither of those savings figures may compel you to rip out your existing water heater to upgrade to a new heat pump water heater. I do recommend you consider your options when replacing an old or broken water heater. For similar or lower lifetime costs, heat pump water heaters can provide hot water to your home with less than half the C02 emissions.

The Key to Tackling Climate Change: Electrify Everything by David Roberts

Home Power Magazine: Air to Water Heat Pumps for all-electric hydronic heating

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