Show HN: Heat Pumps, Hooray – A heat pump calculator for your home(heatpumpshooray.com) |
Show HN: Heat Pumps, Hooray – A heat pump calculator for your home(heatpumpshooray.com) |
It allows you to make a simple 3D model of your home, enter its current state of construction (insulation, HVAC system, roof, solar panels, etc.), and then uses the DOE's energy plus (e+) software to run energy analysis for different scenarios of modification to the building.
For example you can find the optimal balance between improvement to your insulation vs getting a more efficient HVAC system in terms of dollars or energy usage, depending on your goals for your home.
One thing we've built but not yet included in the site is a way to back into a more precise heating/cooling load for the home using past utility bills. That could be useful even for folks going down the more bottoms-up modeling route as a way to help with the 'garbage in / garbage out' problem of having to estimate insulation, window heat transfer, etc. etc.
During our explorations, we realized really struggled to find good calculators out there for understanding the impacts a heat pump can have on your specific home.
So… we built one! It’s free to use, and we’re curious to get your feedback.
Feel free to try it out here, and let us know what you think!
And the chart that is shown peaks in winter a couple months early.
Overall, it seems to significantly underestimate my energy costs.
The conclusion is also confusing: it says I would save $89/year or $24K in 15 years. Huh?
$89/year doesn't seem like enough to justify any investment, and $24K is about $1600/year or ~95% of my current costs, which seems too high to believe.
On winter peaks, I'll have to look into what you're seeing -- we pull weather data from the nearest ASOS station to your zip code and have done a fair bit of validation on that data, but it could be a number of things. If you're interested, you could send the inputs you're using to pumpers@heatpumpshooray.com and I'll do a little digging?
I entered :
- Zip 56714
- 2500 sqft
- 4 occupants
- 1 boiler
- no aircon
- natural gas
and the result was :
Switching to a heat pump will increase your cost by... $257.28 per year
So i'm not entirely sure it works as you intended, or natural gas is much cheaper than electricity. Over here, Natural gas is currently at €2.96/m3 (about 2.5x the price last year), and every calculation we've made based on the heat pump vs natual gas shows it will reduce our annual bill by about 50%.
I've had the heat pump for 6 months, and while it was spring/summer with reduced need for heating, the total consumption of the heat pump in those 6 months has been around 900 kWh, and i estimate around 2000 kWh for the winter. (2000 sqft house, well insulated compared to US standards)
It's acting like I'm buying a separate A/C for each zone, but that's not how they are priced. I have 9 for "Heat pump: Number of units", and 2 for "AC equipment: Number of units ".
Also it's having trouble doing the math right because I have window A/C, but I would get a mini-split for A/C and Cooling.
For me the math is just not right - if I put in a mini-split to have A/C, I need to decide what's cheaper, running my high efficiency boiler (that I already have), vs heating using the heat pump.
That's really all I want to know: What costs less, heat with gas, or heat with electricity. Or maybe a hybrid.
This seems geared more to people who have existing ducted A/C with a furnace (not a boiler), who might get rid of the boiler part, and leave the rest. (Or just not use the boiler.)
IMO you should just stick to calculate fuel costs for heat with gas, vs heat with electricity, and leave out the installation costs.
If you're choosing 'multi-zone', "Heat pump: Number of units" corresponds to the number of _outdoor_ units, rather than indoor heads. For all other configurations, it maps to both outdoor and indoor (the others are all single zone). So, if you want to go with a multi-zone heat pump, I'd suggest entering 1 or 2 for "Heat pump: Number of units" (or just leaving it untouched, in which case the model will choose automatically based on home size).
> IMO you should just stick to calculate fuel costs for heat with gas, vs heat with electricity, and leave out the installation costs.
Roger that. We started out that way, and the cost-to-install was the number one thing that people asked us in follow-up questions, so we added some high-level guidance. I think the lack of transparency on upfront costs and pricing is a major issue for the transition broadly and a problem that needs to be solved -- that's high on our minds.
> That's really all I want to know: What costs less, heat with gas, or heat with electricity. Or maybe a hybrid.
Helpful! Related to the previous point, we want to make it easier for you, with a proposal from a contractor in hand or existing equipment already installed, to choose that equipment from among what we're analyzing (rather than only seeing cost savings for the most efficient unit that we choose automatically). In your case, you'd then be able to see exactly the cutoff points when your existing fossil fuel equipment is (a) necessary because of reduced heat pump capacity at lower temperatures, or (b) cheaper to run than the heat pump. FWIW, (b) is far rarer than we thought going into this exercise.
I have a bug report I got "1.5e+2% of your annual heating."
We model decreasing heat pump capacity and efficiency as the outside air temperature declines. Yes, heat pumps do lose capacity and efficiency the colder it gets, but they can still provide heat even when it's very cold out (there's heat energy in the air until absolute zero, or -273, after all!). You can see that declining efficiency if you expand the "Step 2: Choosing your ideal heat pump" section. We'll add a graph of capacity relative to outside air temperature as well.
Backup heat is still often necessary for many homes in cold climates, but it's necessary a lot less often than you might think. Note that in the results you'll see for the site, backup heat is included if necessary for single-zone centrally ducted heat pumps, but not for any other ducting types.
Efficiency does decrease since they need to spend more time defrosting.
https://www.vaillant.com/home/products/air-to-water-heat-pum...
Maybe a down arrow and advanced?
Also as a non USian without a zip code, this is fairly useless to me.
Yes, unfortunately we haven't seen great resources for the rest of the world, either. The same approach and core model here would work elsewhere, but we'll need to source historical data on housing stock, residential energy prices, grid emissions, weather to get it up and running elsewhere. If you know anyone that would be interested in taking that on, definitely let us know!
also
"Total savings over a 15-year period are up to $37,000"
I must be missing something cause that doesn't add up.
We've tried to make this a little clearer in the "receipt view", but the major difference is in terms of cost of the hardware.
Furnaces, heat pumps, and A/C units all have a 15-20 year useful lifetime.
While the annual savings will be only a bit less, the hardware cost will be _significantly_ less because you only need a one unit for a heat pump vs two for an A/C + furnace combo.
Does that make more sense? We'll try and clarify in the UI
I don't see how you can possibly save $37,000 just by getting rid of the furnace - they just don't cost that much.
Not so good :-(
I guess heat pumps aren't great when it's really really cold?
1. Air-source heat pumps are getting better and better, quickly, so that answer is changing
2. 93% of US homeowners would save money with air-source heat pumps vs. their existing equipment, and only 3% of homes would see an annual utility bill increase above $70. (these from backtesting the national sample of homes from the EIA's RECS survey)
A lot of people think "really really cold" means it hits zero a few times each winter. They don't know what living in Fairbanks is like :), and chances are that heat pumps can keep up with their local weather.
See this seems to me an illustration of something being hinky about the discussion.
"Hits zero a few times each winter" quite possibly is an accurate description of the climate where I live. I believe only one month had a below zero low recorded last winter.
But representing my climate with that particular factoid would gloss over that lows around freezing down to subzero are typical for like six months of the year, and the other six months, you don't need heat in the first place.
A lot of people in the CONUS really do live where winter is pretty harsh, not just North Dakota or something.
The important thing for saving on energy bills, which I don't ever see brought up in any online discussion about heat pumps, is how bimodal the climate is, not how extreme the winter lows are.
I can't say there is nowhere in the world where the temperature graaaaaaadually ramps up and down all year. But all I see is people taking for granted that's how it works and thus heat pumps spend a large amount of time in the optimal range.
If you're set on electrifying there, it might make more sense to investigate a ground-source heat pump which leverages the ambient underground temperature for heat exchange.
1/ Right now, if you select "No A/C", we still include the cost+emissions of cooling from the heat pump. It's on the backlog to add a "heat vs. heat only" comparison. In part, we're assuming that if you have cooling capability, you'll probably use it (and therefore wanted to include that in the emissions impact), but also that homes without A/C today will have small cooling loads to begin with, so it wouldn't change the answer too dramatically. For now, I'd suggest looking at the monthly costs in the summer on the bar chart and mentally adjusting the headline number for those. Sorry that's not smoother!
2/ Natural gas is indeed way cheaper here -- dramatically so this year, but previously as well. The backtest shown on the site is Feb '21 to Feb '22 -- natural gas prices this coming winter are bound to be much higher than they were last year, so savings numbers will definitely change going forward. It's on our list to (a) make that dynamic clearer on the site, and (b) explore a more forward-looking savings number. Right now, the annual energy costs are "what you would have saved _last year_ vs. your existing equipment", instead of what you might expect, thinking that would be more convincing / less controversial, albeit potentially conservative.
Thrilled to hear you're 6mo into life with a heat pump! Is it air-to-water and still using water/steam radiators, or forced air now?
It was the logical thing to do. Even before the war in Ukraine, the ROI of the heat pump was 8-10 years compared to natural gas. With current conditions, shortage of natural gas, inflation and more, the ROI is around 4 years.
> Is it air-to-water and still using water/steam radiators, or forced air now?
Pretty much everything regarding heat in (northern) Europe is based on water, with the exception of hotels that usually use either only air or a combination of air/water.
Our particular installation is from the 1970s, meaning it's 1 string and made for much higher flow temperatures than the houses from 2000 and onwards, so instead of a 35C flow temperature we instead have a 55C flow temperature, which reduces the COP value of the heat pump.
My particular model (https://www.vaillant.com/home/products/air-to-water-heat-pum...) has a COP value of (up to) 5.4 with a flow temperature of 35C, which gets reduced to around 4 with a 55C flow temperature.
I've coupled mine with radiator thermostats from Tado (https://www.tado.com/gb-en/products) which use geofencing to lower the temperature when nobody is home, and they also have a "sensor/control unit" for the heat pump control itself, allowing fine grained control of the heat pump. One of their upcoming features is to try to optimize heat pump usage for when electricity is cheap.
That is the amount of heat you require over a year.
Through the magic of heat pumps, you can find the COP value of any model you plan on purchasing, but in essence the COP value tells you how much heat the pump will produce when using 1 kWh of electricity, for instance a COP value of 3.62 means the heat pump will produce 3.62 kWh of heat for 1 kWh of electricity.
So say you have a yearly gas usage of 1600m3, that equals 16880 kWh of heat. Assuming a heat pump with a COP value of 3.62, you can then divide the 16800 by 3.62 to find the amount of electricity you will need with that particular heat pump to produce the same amount of heat, in this case 4663 kWh.
As i said, this is a very crude calculation, and it doesn't take into account that the heat pump efficiency drops as temperature drops to around it's lowest efficiency temperature (for mine it's -25C). When that happens, it has a built in backup heating device that will do regular electric heating, meaning 1 kWh per 1 kWh.
It also doesn't take into account climate control built into many european heat pumps (and maybe american as well ?). Mine has an outdoor sensor that simply shuts off the heatpump whenever outside temperature goes above a certain point.
And then there are all sorts of after market upgrades you can buy, like Tado, who produces a "sensor" for certain heat pump models, which will further reduce consumption based on local weather forecasts, AI and other readings.
You're right that our site doesn't yet work for homes outside of the US, unfortunately. The approach would be similar, but some different equipment and home configurations to consider along with different data sets (fuel pricing, weather, grid emissions, etc.) -- I'll keep an eye out for good resources, and would love to help anyone who wants to try to build it!
The best is to have a hybrid system: a heat pump and a gas/oil/wood boiler which will fire up when it is freezing.
Some of the things driving speed:
- Fetching hourly weather data -- we use binned data for the 15-30 years used for equipment sizing and selection, but for the 12 month backtest to get savings and emissions, we're going hour by hour through the last year for the simulation.
- Loading + merging emissions data -- same deal for hourly grid emissions for your local grid, to get emissions from electricity usage (though we do make some assumptions about the grid decarbonizing when we show expected lifetime emissions figures).
- Simulating thermostat behavior -- we do some extra processing before the core simulation to model realistic human behavior on thermostat setting, so that you don't get lots of flipping between heat+cool in shoulder months or the furnace kicking on in June just because it hits 68dF in the middle of the night.
- Heat pump equipment selection -- we're doing a slightly simplified version of the backtest over 15-30 years of historical data for ~2k heat pump units (depending on ducting type) as a bake-off to choose the most efficient-but-properly-sized heat pump for the home. There's more optimization to be done there, but it's about 2-3s of the total time currently.
- Backtest itself -- once we have the equipment chosen and the weather + thermostat scenarios created, we run the simulation itself for the last 12 months, twice (once for the status quo equipment, once for the heat pump configuration). That goes through each hour of the year, simulating heat load on the home (outside weather including cloud cover and solar positioning, humidity, wind speed, temperature, plus internal loads like appliances and the heat occupants give off), simulating equipment performance (for heat pumps, a function of output, outside temp, inside temp, outside humidity, altitude, and layering in backup heat as applicable/needed), plus accounting for surplus/deficit heat that needs to roll over to the next hour based on thermostat settings or insufficient conditioning, etc. etc.. With usage, we then compile and calculate the utility bills monthly (we have support for actual rate plans, TOU plans, etc., but for now we just use statewide marginal retail prices from the EIA for the site version, because those tend to be conservative) and also calculate emissions, which is time intensive for electricity given we're layering in actual emissions from the grid in the simulated hour.
Anyways, there's definitely a lot of optimization we could do to get the processing time down, but hope that gives you a sense of what's going on server-side. Also, the model we're running is more flexible than what's exposed on the site currently (e.g. arbitrary date ranges for the backtest), and if we made a more specialized version of it, we could do a lot more pre-computing.
Rotating the display to landscape shows the full numbers, so it’s a styling issue, not a content issue.
I was hoping to see an air-to-water calculator as hydronic heat is common in New England. If that equipment wasn’t so premium-priced and hard to find experienced installers, I think a lot of conversions could happen.
And thanks for catching the issue on mobile, we'll get that fixed asap.
The Manual J (industry standard approach to load sizing) uses 70 dF for heating and 75 dF for cooling as its defaults, so we could definitely update the defaults to those, too.
I guess I can try their model and find out.
In the US, if you need backup heating (and you may not, with the heat pumps that are on the. market today), electric resistive heating (heat strips/coils) is indeed more expensive than high-efficiency gas furnaces BTU-for-BTU, but remember that resistive heating runs in parallel with the heat pumps, whereas furnaces have to take over entirely for dual fuel systems. Natural gas might be cheaper than electric resistance alone, but electric resistance plus the heat pump even at diminished capacity can be a very different story.
(The huge win is the 99% of the year where supplemental heat isn’t needed.)
People advocating for heat pumps seem to be convinced the normal climate, if it isn't warm all year round, is in-between for most of the year. I have never learned why.
Where I live, and it's not Alaska, northern Minnesota or Maine or something like that, there can't be any "win" for six months of the year because there's essentially no need for burning gas anyway. That's separate from the question of exactly how cold a heat pump can be effective.
But from November through April, lows here range from the high 30s to below zero (F). Based on some poking around .gov websites, that is plausibly well into the resistive range.
And again, it doesn't matter how well it works above 40F, because all of the months (6) with lows above 40 require virtually no furnace use.
I've been told that my experience with a heat pump in an apartment where it had to be set to "emergency" (resistive) heat all winter is outdated...but I can't shake the feeling that people are not understanding climates where heating is needed in the first place.
Why is that? I see no reason you can't run both, other than a more complex thermostat setup - probably something with an outdoor reset, that kicks in when outside temperatures are too low.
Even on a day with the low in the teens, the high was probably 10-15° higher. Look at the hourly bin data for your location, not just the daily/monthly lows.
The key with a heat pump in a heating dominated climate (on top of insulation which is needed for any energy source) is sizing it right, creating the ducts right, setting the control strategy to not use H2 (emergency heat) too liberally, and not using deep setbacks that will flip you into H2.
Just as you are rightly skeptical of people who can’t comprehend not installing AC, you might be skeptical of drawing too strong and long conclusions from one heat pump install in a rental of unknown quality and where the incentives aren’t aligned to trade-off capital vs operating costs.
[1] https://www.pacificairconditioner.com/files/Hyper_Heat_for_r...