The Heat Pump debate

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The motivation to switch to a heat pump is often rooted in the desire to reduce heating costs. I get that.

High heating costs are typically associated with inefficient buildings that have a poorly insulated and drafty building envelope. Such buildings would need a rather large heat pump with a ducted or multi-zone set up, or even several heat pumps.

Our building with a subpar building envelope prior to any improvements

Anecdotes from heat pump forums, acquaintances, and friends indicate that owners of buildings with a subpar building envelope often regret switching to heat pump – mainly because their electrical bills went through the roof. If building owners assume that heat pumps are a quick fix, their conclusion that heat pumps are a waste of money, and that it is cheaper to heat with natural gas, is on fairly solid ground. But if building owners approach heat pumps as part of a broader systemic plan, heat pumps can and do generate significant cost savings. 

The system approach

We have a masonry building, built in 1902, with three apartments. Each apartment has its own airsource heat pump (single head minisplit), which is placed centrally in each apartment.

They run great! They provide the needed cooling during the summer and just about the right amount of dehumidification. They provide the needed heating during winter, even during spells of subzero temperatures. And they heat significantly more cheaply than our hydronic baseboard radiators that are powered by a high efficiency natural gas boiler.

But why?

The minisplits are only ONE component in our system approach. Preceeding and prerequisite components in our system approach were the improvements to the building envelope during our deep energy retrofit, which allowed us to substantially reduce our overall energy load: Roof insulation; wall insulation; foundation insulation; basement slab insulation; triple glazed, airtight windows; insulated exterior doors with good weather stripping; air sealing; etc. All these efforts reduced the energy load of the building by around 2/3 and catapulted us into cost-effective airsource heat pump territory.

Now that we had reduced our energy load, I could build on it with the next component: “right sizing”. I hired a competent energy auditor to run an energy model for each of the three apartments to determine the heating and cooling load.

Undersizing heat pumps is not a good idea as it will be difficult at times to keep the building warm or cool enough. Oversizing heat pumps introduces its own problems, such as short cycling, which in turn reduces efficiency and comfort, and can lead to insufficient dehumidification during summer.

The results from the energy model allowed us to go shopping for the “right sized” equipment.

We installed a 9,000 Btu cold climate Fujitsu minisplit in the garden unit (900 sf), while the 1st and 2nd floor apartments (1,500 sf each) have a 12,000 Btu cold climate Fujitsu minisplit each.

In addition to the heating and cooling loads, I paid close attention to the moisture removal capacity of the minisplits, to make sure they deliver a comfortable relative humidity level during the dog days of our Midwestern summers.

For us, the next component in our system approach was looking into a renewable energy source. Because our space conditioning load was drastically reduced, reflected in the three relatively small heat pumps, we could power them with our photovoltaic roof array. The result, thanks to our net metering agreement, is next to no heating or cooling cost.

Our electricity cost per household compared to the Illinois average. Our electricity use includes all cooling and most of the winter heating with our minisplit.

Taking a system approach, we were able to turn the paradigm on its head: Our high efficiency natural gas boiler cannot compete cost-wise against our heat pumps.

Disclaimers

But it’s not all unicorns and rainbows.

Heat pump installation requires professional expertise, attention to details, and skills, in particular when it comes to sizing and the flare connections. To avoid a never-ending loop of service calls, it is a good idea to be picky about who you let near your heat pumps.

Yes, the right heat pumps work in freezing temperatures. Our cold climate minisplits even powered us through a brief polar vortex with subzero temperatures. However, the colder it gets, the less efficiently they run. I observed that our heat pumps notably lose efficiency once we drop below 20F. They still do the job. They just draw more power.

Heat pumps are likely to run differently compared to your old heating system. If you had forced air, you turned it on and it was warm 10 minutes later. That is unlikely to happen with heat pumps. They ramp up slowly but efficiently. With heat pumps, you can enjoy more even temperatures, day and night.

Heat pumps can emit an unpleasant stale and moldy smell in the summer (see also this blog post). This happens when they run in cooling or dry mode and are turned off. The remaining condensation on the coil of the indoor unit combined with dust particles is the perfect petri dish to grow mold. This can be avoided by running them in fan mode for a few hours before turning them off. That will dry off the coil. No moisture, no mold.

And like everything else in a house, heat pumps require regular maintenance. You want to make sure to regularly clean the filters and drain lines. Also inspect the outdoor and indoor coils, and the indoor blower wheel, and have them cleaned by a professional when needed.

These are not deal breakers, at least not for us. But it’s good information to have, in case you also want to turn the paradigm on its head.

Related posts:

Five years of solar – Comparing (Part 3 of 3)

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In the previous two posts of our photovoltaic system, we reviewed the amount of kWh we used and produced, and our electrical cost. But how does our electrical consumption and cost compare to other homes in Illinois?

To find out, I took the data per solar year for our 4,500 sf building (kWh used and cost) and divided it by the three apartments to have a per-household baseline, which I compared against the residential average monthly bill data for Illinois published by the U.S. Energy Information Administration (EIA).

Since we activated our solar array on December 24, 2019, I show data starting with solar year 2020. The latest EIA data available is for 2023. 2024 data has not yet been published, so I will skip that year.

Electricity consumption

Broadly speaking, our electricity consumption per household/apartment is about half of that of the average Illinois household, or less.

What these numbers show is that our investment in the building envelope improvements paid off by significantly reducing our overall energy load. I am talking about good insulation, good air sealing, good quality triple glazed windows, good exterior doors, a high quality and highly efficient ventilation system, etc.

What also helped was us being picky about what appliances we bought. They were almost exclusively Energy Star rated appliances. And not just any Energy Star appliances. We picked the ones that had the best (or one of the better) efficiency ratings.

Cost and bills

If I use solar year 2020 as a baseline, the Illinois average annual electricity cost per household was 8.4 times our cost, thanks to our solar roof array. And 2020 is the best year to focus on, since the only heating source was our air source heat pumps.

This significant cost reduction reflects that our investment in the building envelope improvements reduced our overall energy load, plus the electrical production from our 8.58 kWh solar roof array reduced the amount of electricity we had to purchase.

Let me say this again:

I started two posts ago with bragging rights because we generated a surplus two years in a row. That is an encouraging data point. The real bragging rights, however, are less in the surplus and more in the relatively low electrical load that we have been able to achieve and maintain.

We were not distracted by the low hanging fruit: “Let’s switch to all LED lighting…”. I credit our motivation to eliminate unnecessary energy hogs (such as the proverbial old refrigerator in the garage), our selectiveness in picking right-sized and efficient appliances, AND most importantly, our laser sharp focus on the building envelope improvements during the deep-energy-retrofit. The latter gave us, without a doubt, the biggest bang for our buck.

In the next post I’ll explain, at least partially, why the building envelope improvements were such an important investment by using our air source heat pumps as an example.

Related posts:

Five years of solar – Cost (Part 2 of 3)

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To continue the five year review of our solar array, our annual electricity bills reliably follow the trends outlined in the previous post, with the exception of the solar year 2024. To explain this outlier, we need to take a look at how deficits and surpluses as well as fixed costs affect the billing.

This analysis is mostly relevant to ComEd customers in northeastern Illinois with a net-metering agreement. Customers with other electrical suppliers and in other service territories are likely subject to different tariffs, charges, and agreements.

We find three billing categories on our ComEd bills:

  1. Supply costs are the cost for the electricity (kWh) we pulled from the grid (supplied by ComEd). If our solar production per given month is larger than our electrical consumption, this zeros out.
  2. Delivery costs are also often referred to as fixed costs. These are the costs for having an electrical meter and a connection to the grid (grid tied system).
  3. Taxes & fees are a percentage applied to the electricity (kWh) we pulled from the grid (supplied by ComEd). If our solar production per given month is larger than our electrical consumption, this zeros out.

The chart above shows the cost per solar year for each of the three billing categories, plus the total annual cost, since we activated our solar array on December 24, 2019.

For the three apartments in our 4,500 sf building, our annual electrical cost started at a “whopping” $403.71 for solar year 2020. Not that surprising, considering that this was also the solar year where we ran the biggest deficit.

Equally unsurprising is that our lowest annual cost was $141.44 during Solar year 2023 with the 995 kWh surplus. Because of that surplus, we incurred no supply cost and taxes & fees. What stands out is that our annual cost rose to $170.55 in 2024, despite the 715 kWh surplus.

That increase is due to the rise in the delivery cost (fixed fees) during solar year 2024 by a total of $29.10. And as long as we have an electric meter and a connection to the grid, we will be subject to the delivery cost.

And what happened to our surplus? Think of it as a charitable donation. With our net metering agreement, at the end of every solar year, our account is reset. If we run a deficit, we need to pay up for the electricity we pulled from the grid. If we run a surplus, it will be erased and we start at zero for the next solar year.

With solar vs. without solar

We just established the bill total for the whole building per solar year with our solar array. But what would we have paid if we did not have the solar array on our roof? Well, there is a spreadsheet for that.

Broadly speaking, we would have paid around $1,500 for electricity per solar year for the three apartments in our 4,500 sf building. That translates into roughly $1,200 to $1,300 in savings per solar year.

These are real “feel good numbers”, which are in line with the savings prediction we got from Lisa Albrecht at All Bright Solar (our solar installer), during our consultations with her when we went down the solar road.

Related posts:

Five years of solar – kWh (Part 1 of 3)

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Two years have passed since my last review of our photovoltaic roof array, which we activated December 24, 2019. And since we produced our first surplus during the solar year 2023, followed by another surplus for 2024, I feel it’s time to brag – a little.

Consumption

In the five years since we had our 26 module, 8.58 kW photovoltaic roof array installed, the electrical consumption for the three apartments in our 4,500 sf building ranged from 13,428 kWh at the high end per SY to 10,574 kWh at the low end.

I attribute the rather high electrical use of 13,428 kWh during solar year 2020 to the fact that all heating was provided by our air source heat pumps, and a cold spell that swept through Chicago with temperature in the single digits during the month of February.

The lower annual consumption during solar year 2022 and 2023 was partially due to user behavior (using the natural gas powered radiators for heating rather than the air source heat pumps), and milder weather conditions during the heating season.

Production

The electrical production varied over the past five solar years due to a number of factors. It is, however, difficult to exactly quantify what factors may have had what impact.

The solar modules lose some efficiency over the years. Our modules, the Panasonic N330/N325, have a specified annual degradation rate of 0.26%. This would be hard to notice or measure year over year.

It is much more likely that weather and/or shading conditions as well as soiling of the panels are the driving factor for the variation in production. That said, it does not explain the decline from 11,390 kWh during solar year 2020 down to 11,052 kWh for solar year 2021, considering that the percent of possible sunshine increased from 56% to 58%.

The drop in percent of possible sunshine between solar year 2021 and solar year 2022 from 58% down to 50% may, however, explain the production drop from 11,052 kWh to 10,319 kWh.

The uncharacteristic jump in production to 11,633 kWh for solar year 2023 and 11,801 kWh for 2024, can be partially attributed to the rise of the percent of possible sunshine to 57% and 58% respectively. However, production was still higher than solar year 2020 and 2021, which had almost identical amounts of percent of possible sunshine.

What may account for the difference was the removal of a dead Ash tree [LINK – Photovoltaic roof array shade study] on the adjacent property. Prior to the removal (solar year 2020, 2021, and 2022) that Ash tree partially shaded our array in late fall, winter, and early spring (see also video below).

Surplus

For the first three solar years our electrical consumption outpaced the electrical production, and we ran small deficits.

That changed during the solar year 2023 with a production surplus of 995 kWh, followed by a surplus of 715 kWh in 2024. This surplus does coincide with the above mentioned jump in electrical production. But it probably also needs to be attributed, at least partially, to user behavior and weather conditions.

For example: The smaller surplus for solar year 2024 is due to the increased electrical consumption, which I attributed to a slightly higher air conditioning load compared to solar year 2023.

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Paint removal from door hardware

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Our house came with beautiful door hardware when we bought it back in 2009. Almost all of it was solid copper.

But we had no clue, because it all was covered with multiple layers of paint. So much so that some of the finer ornamentations were no longer visible. That turned out to be a blessing in disguise, because the scavengers that extracted the copper pipes before we bought the building didn’t know either. They walked right by the real treasures that were hiding in plain sight.

Needless to say, once we discovered what we had, we were eager to restore and reuse the hardware, just like we did with the original wood trim and doors. But what method to use?

While walking through the building with another building nerd (can’t remember who it was), he suggested the crock pot method:

Take an old crock pot that you won’t use any longer for cooking. Place your hardware in the pot and cover it with water.

Then let it simmer for several hours, until the paint is nice and tender and flakes right off!

I know! Not only does it sound simple, it actually is simple. And easy! We had to do some fine cleaning with small wire brushes and some polishing, but the crock pot did all the heavy lifting. I can’t emphasize enough what a time saver this method was. And no nasty chemicals involved!

Used crock pots are often available for a very low price at thrift stores. Buyer beware – be sure to search for the model number online to see if the one you’re considering has been recalled.

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