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1. Just today I decided to run a sanity check on some calculations for heat pumps vs high efficiency boilers (furnace) in UK homes. Much depends on the price of fuel and electricity. It turned out that the figure of grammes of CO2 per KWh for electricity was twice our current value.
   As an aside, as the temperature falls, so does the COP efficiency of the heat pump. I figured that once the COP falls below 1.9 the boiler/furnace is cheaper to run. If the COP falls below 1.2 then the heat pump produces more CO2 than the boiler/furnace.
   I have no notion of the temperatures that might drive these changes.

   1. Hi there, Richard. You’ve raised some useful issues here. You bring three perspectives – efficiency, CO2, and cost of operation – to the table, so I’ll start with the efficiency part and address the others toward the end.
      In North America we have 3 different types of heat pump systems – single-stage, 2-stage, and variable capacity. Except in New England and in a lot of commercial buildings, gas-fired boilers are not nearly as common as gas forced air furnaces, but we have the same options as Europeans do when it comes to boilers. Condensing efficiency systems, both furnaces and boilers, are becoming very common. They have efficiency ratings (AFUE here) typically between 90 and 96 percent. Heat pumps here have an HSPF (Heating Season Performance Factor) rating. I emphasize ratings because the ratings aren’t comparable at all, and the testing and rating procedures do not at all reflect how the product, or the whole system (with all of its pumps, fans, duct or piping losses, etc.) will actually perform in a building.
      If everything were rated with a Seasonal COP, for specific climates, then they would be comparable, but only if tested while operating as they do in the building, which they aren’t, yet.
      The furnace and boiler testing is done at a steady-state full firing rate, and the rating does not include any of the electricity used by the product. The COP of a 95% AFUE furnace (only the gas combustion efficiency while the furnace is running steadily at its maximum rated output) is 0.95, and is largely independent of the outdoor ambient conditions. However, to heat the building as the heating load varies with outdoor temperatures, the system starts and stops, which creates what are called cycling degradation losses. In the mildest heating conditions – say 10-15C – the system starts and stops a lot, and the losses can be more than 25% based on the lab testing we’ve done. If we add these losses in, and we add the electricity used, which for a forced air furnace with a not-so-good fan can be quite a lot, you end up with a seasonal COP of about 0.75. And if you add ducting or piping losses, you’ll be down in the range of 0.67-0.74. A LOT lower than the ratings you’re probably using for your comparisons.
      Heat pumps have their issues, too, as you point out. They’re not tested and rated in a way that is representative of how they operate in a building either. Until now. For the last several years I’ve been the co-chair of a Canadian Standards Association (CSA) Development Committee that created a whole new set of procedures to test and rate heat pumps and air conditioners, called “load-based testing.” The systems are tested with a load that’s representative across a wide range of outdoor ambient conditions, operating under its own controls. The resulting Seasonal COPs, for each of 8 climate zones, are quite different than with current testing and rating.
      Single-stage heat pumps turn on and off under low-load conditions, just like the furnaces and boilers, so they have cycling degradation losses, too, and only slightly lower than for the gas-fired equipment (15-20% under the lowest load conditions mentioned above). Two-stage equipment improves that quite bit by being able to operate using longer cycles at lower capacities in the low stage. However, the variable capacity equipment nearly eliminates cycling degradation losses by being able to vary output across a wide range of capacities, to match the wide range of outdoor conditions. Their Seasonal COP ratings using our testing regime are quite a lot better than the older technologies – typically between 3.2 and 3.6 in the heating mode.
      When it comes to capacity and efficiency, your concern about low heat pump COPs is probably misplaced, but that’s because you’re having to use ratings from a poor testing and rating regime. It’s true that at very low temperatures (say -15C), COPs can fall below 2.0, and for the older technologies, capacity starts to fall off at about 0C, and for many models will be less than 75% of full rated capacity by -15C. However, the cold-climate-capable variable capacity models hold their full rated capacity down to -15C before it starts to fall off. COPs for these tend to be around 2.2 to 2.3 at -15C.
      However, a seasonal rating weights the COP performance by the number of annual hours that outdoor temperatures are experienced in each climate zone. For instance, in North America’s typical coldest climates (like those in Minnesota or Manitoba), the number of operating hours below -15C are only 8% of the total heating season operating hours. Most of the hours are between 0 and 10C, where the heat pump COPs are much higher (over 3.0).
      So when one does comparisons of performance, especially if you’re looking at CO2 and annual cost, you should use annual ratings. Fortunately, I’ve gathered enough data over the last 25 years or so, in the lab and in buildings, to have a pretty good handle on those, but most people won’t have access to that needed information until we test and rate appropriately. We’re working on that. There’s an ISO Technical Committee (TC86) evaluating our CSA work now.
      When it comes to CO2 and operating cost, as you point out, it’s very energy utility-specific, and it changes over time. If your electric grid is coal-heavy, electricity will have a higher CO2 footprint, of course. If you had a 100% renewable grid, it would be much smaller. You’re also (I think) looking at CO2 production at the site where the equipment is being used. However, the actual CO2 footprint of a fuel starts at the mine mouth, literally in the case of coal. Fossil fuels have a very hefty CO2 footprint before the fuel or the electricity it produces reaches your home or business. The digging/drilling, processing, transporting, refining and delivering generate a LOT of CO2 that most people either aren’t aware of or would prefer to ignore. Fracked natural gas is particularly ugly in that regard. I took all of that stuff into account when I did my first impact comparison for heat pumps and condensing gas furnaces (for the Oregon Public Utility Commission) back in 1994. At the time, all it took was a seasonal COP of 2.4 for the heat pump to win the contest. Granted, our Pacific Northwest electric grid was 40 percent legacy hydropower at the time. But since then, all but a tiny fraction of our coal-fired electricity has been retired, and the heat pumps have gotten a lot better (while the gas furnaces really haven’t). Since 2005, half of U.S. coal-fired generation has been retired and things are still moving in that direction. So any analysis will have a limited shelf life these days.
      Costs, too, are utility-specific. My utility is a co-op and has very low rates. People in New York and California here in North America aren’t so lucky. And projecting future costs is a perilous exercise anymore. So I don’t give comparative cost too much weight.
      As I try to convey, I tend to see things in a “whole system” perspective, taking all of the nuances I can learn about into account when I’m trying to make good decisions about how to conduct myself as a human here on our beautiful planet. I’m always happy to help others in that regard where what I’ve learned is useful. Hope I did a bit of that here. Let me know if I’ve missed anything. Charlie

2. Mr Stephens, will you do a speaking engagement geared towards facility managers? Either in-person or virtual, I am on a committee to schedule the 2024 year events and I believe the facility managers (for commercial buildings) would benefit to hear from you!

   1. Hi, Sarah. I would likely have to do this as a virtual thing, but absolutely – yes, I’d be happy to talk with you about what you would like to have me address. As it happens, a lot of my work right now is in reducing the energy use of HVAC systems in commercial buildings – of all occupancy types. Our typical HVAC energy savings, on an EUI basis, are 70 percent. You can send me an e-mail at cmstephens14@icloud.com and we’ll figure out a time to talk. I don’t charge for my time in this work anymore – it’s just a passion of mine in semi-retirement. Charlie

      1. Thanks, I’ll send you an email, looking forward to it. ?

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