Air to Water Heat Pumps
Comments
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Adam is measuring his Cop and SCop by monitoring equipment that uses a energy meter on the electrical feeding the HP only and a BTU meter reading the feed and return piping of the HP. There is nothing except the HP between these two points. Though there is a kit that has monitoring with a btu meter for DHW also. PV is not taken into account in any of these measurements.
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
You are correct, Looks like a product placement for that battery backup was thrown into the presentation :)
Here is the steps they consider. The lowest step being radiation sizing.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
When you get to the lower steps you are hitting SCOPs that beat geothermal. Geothermal is considered expensive. If someone has money for geothermal then the thing to do is convince them to spend the money inside the house with a great hydronic design like radiant heating. Tell them to leave digging holes in the ground to there dog.
SPending the money inside the house leads to greater comfort!!
ITs a great time to be a hydronics designer!!
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
I think you are getting a bit carried away with your recent Heat Geeks course. Their online stuff is really good and they are spot on with many of the things they are saying. Their experience is mainly UK based where the climate is quite mild: typical min outside design temp of -2c (19f) and in a heating season 50% of heating energy at an outside temperature below 6c (43f) and the other 50% above. Your comment re Geothermal is true for the UK.
The Carnot Cycle equation contains a term of the form 1/(Thigh-Tlow). If Tlow is a low number no amount of radiators and insulation will make a difference.
If you were to design a system for outside temperature -18c (0f) and radiators at 30c(86f) - 25c(77f) the theoretical COP would be 5.56 and for a real heat pump (40% of Carnot Efficiency) 2.5. For this example the radiators are 13 times bigger than ones rated at 75c-65c (167f-149f).
I have prepared a short document that might be of interest to you and other calculator warriors.
There is a good website for radiator performance:
that covers the maths and allows you to play around with values.
John
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Some of the Heatgeak design goals are good, some I'm going to disagree with in cold climate.
DHW off the heat pump is a bad idea for efficiency, COP tanks bellow freezing weather. I can also tell you management will never buy in on lower DHW temperature, tried it and got vetoed.
Pipe type won't make a difference. You can get a low loss distribution system with any pipe, no need for full bore copper. Even if slightly restrictive, the extra pumping power is in the range of 50W, so basically squat, not enough to push the efficiency needle.
The one you do have to watch though is the wall of pumps. I have seen setups where all pumps running used about 1kW, that will definitely effect COP.
Even with floor heat, you can only lower the emitter temps so much. Heated floor that is not hot kindof defeats its own purpose. Bath tile needs a min of about 38C water, you could run hardwood with 30C but that is about as low you'll go. That is still a pretty big delta in cold climate.
Also, is it just me, but I've always pronounced it C.O.P, not "COP". Its like calling an IGBT an "Igbit".
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[I have edited this post to correct some calculation errors I had made]
The question of theoretical COP vs actual COP intrigued me.
There's only one air-to-water heat pump manufacturer that I'm aware of that publishes part-load performance data, and then only for cooling, and that's Chiltrix. It's at:
I got all of their numbers into a spreadsheet, and I charted 63 data points for efficiency vs temperature delta (in C). Note that efficiency is defined as observed COP vs Carnot efficiency. Here's the chart:
The highest observed efficiency is 29.44% which is seen with an outdoor temperature of 35C, water temperature of 7C and delta of 28C.
Just for comparison's sake, this is observed COP vs delta:
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I was interested to see what the effect of part-load modulation would be, in a way I feel the SCOP derby is a contest to see who can get the most oversized heat pump and oversized radiators to work.
Chiltrix provided numbers for 75%, 50% and 25% load. Generally the efficiency numbers were higher the lower the load, although they provided so few numbers at 25% it was hard to conclude anything. The highest efficiency observed was at 50% load, 33.3% of Carnot. That was with 19C air and 7C water.
If you would like to look at the data it is at:
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Nice to see real data. Yes COP does seem to improve with reducing load and I guess this down to heat exchanger theory. Same with a condensing gas boiler where the efficiency goes up dramatically with falling load and temperature.
I have been using data from ATA databook at:
Cooling COP against theoretical is lower for cooling as opposed to heating. Interestingly, the drop off with COP against load seems much lower with R290 relative to R32 refrigerants. If you want to dig in this Mitsubishi data, models with WM in the model number use R32 and WZ is for R290.
John
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The purpose of measuring energy use is to improve efficiency and performance. The simpler the better. We need field data and not advanced math or lab experiments like AFUE that are later proven not to work and nobody does anything about that.. The manufacturer's built equipment to perform better in a lab experiment not real world homes or buildings.
Energy in vrs energy out Energy Out / Energy In = COP. Take this number and average it over the course of a day, week, month or year. You can average it out during a normalized period of weather data to compare one properties performance vrs another. Then set up a competition for the field designers to compete.
That is how you develop technology for energy efficiency. I have been talking about doing this for 35 years now and nobody ever did anything. Nobody in govt wants to listen to real science or engineering or include productive people in what goes on. Productive people aren't profitable. The truth isn't profitable. The narrative that is developed to help major corporations block out competition and sold by lobbyists to politicians is what is profitable is more important.
In the U.K. that is now changing. This group at Heat Geeks and Open Energy Monitor are changing things for the better.
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
OK, one more chart:
This gives some idea of the shape of these curves, but I wish there were more data points. For example, it's impossible to tell whether the curve peaks at 25C delta t and then declines, or whether it flattens out around 20C and is horizontal from there on out. It looks like 75% output is broadly more efficient than 100%, and 50% is more efficient than 75%, but what about 25%? With only four points it's hard to draw conclusions, but it looks less efficient than 50%.
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@John Ruhnke : "We need field data and not advanced math or lab experiments like AFUE that are later proven not to work and nobody does anything about that.. The manufacturer's built equipment to perform better in a lab experiment not real world homes or buildings."
I want to comment on that. We need both.
I think we've all been around someone trying to make a complicated piece of equipment work without knowing how it works. We've all probably been that person — just changing things at random and seeing what happens. Having even a little bit of theory of operation makes that process a lot more efficient and effective. If real-world experience contradicts the theory, that means the theory has to change, that doesn't mean that theories aren't valuable.
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If you're not adjusting for climate the COP numbers are basically worthless. You're having a contest to see who lives in the mildest climate.
It was pointed out to me in a PM that I was incorrect earlier when I said the "SCOP" numbers at the site below were climate-corrected. It turns out they aren't:
OK, so let's look at their leaderboard. Number one is a ground source heat pump. Number two is located in Sint Maarten. This is an island in the Caribbean. According to Wikipedia, the daily mean temperature there is 81.1F (27.3). The all-time high temperature ever recorded is 95.4F (35.2C). The all-time low is 65.5F (18.6C). The coldest month is February, when the average low is 73.8F (23.2C).
This is a climate where you could live quite comfortably without heating or cooling of any kind. And yeah, their heat pump is scoring an average COP of 5.4. I do wonder what they're using the heat pump for.
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"This is a climate where you could live quite comfortably without heating or cooling of any kind. And yeah, their heat pump is scoring an average COP of 5.4. I do wonder what they're using the heat pump for."
Dehumidification?
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Well we could easily do the math and add weatherization to there numbers. Weather data is available at any weather station going back many years.
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
The HeatpumpMonitor.org website allows you to click on any site and see their COP vs Delta-T chart. Here's the one for that site in Sint Martaan:
It looks remarkably like the one I posted above.
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I think the Sint Maarten from is in the Netherlands - near the uk! The delta T values don't look like a Caribbean island.
I agree, ultimately the actual data is all that really matters. Science is the art of creating theories and testing them against data, when the data and theory disagree the theory needs to change. Once the theory is established it defines the boundaries of what is and isn't possible.
For heat pumps the definitive theory was created by French physicist Sadi Carnot in 1824 and since 1840 nobody has come up with anything to superseded it. If heat pumps are you business, you would be well advised to study it. The manufacturers of the equipment certainly have, perhaps their marketing departments haven't.
To quote one of your countrymen:
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled"
R.P. Feynman
In terms of the UK, the government is doing all sorts of things to promote heat pumps, tax breaks and grants including rules that are effectively legal a requirement on design temperatures for radiators. For heat pumps it is 45c(81f). This is bit high in my view.
John
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@JDHW: "I think the Sint Maarten from Site faviconHeatpumpMonitor.org is in the Netherlands - near the uk! The delta T values don't look like a Caribbean island." I think you're right. The Caribbean island is also part of the Netherlands, but there is also a town of that name in North Holland.
On their chart of the past year the lowest temperature shown is -1.2C. So while not quite Caribbean, that's pretty mild.
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A comment on what goes into heat pump performance.
There are three factors that will contribute to the annual power consumption of a heat pump. The first is the climate, which you can visualize with a chart that shows average annual hours at each temperature, like this one:
The chart above is for Washington, DC.
The second is the COP vs Delta performance of the heat pump. This is generally a straight line or close to it, this is the line for a Chiltrix CX34, I posted it above earlier:
In the HeatpumpMonitor.org listings you can see this curve for each installation. I looked at a few, they all have the same linear shape although there is some variation in where they land.
The third part is the outdoor temperature vs temperature delta. This is on the system designer, here are a couple of possible lines:
The red line is a constant water temperature, always 95F. The blue line is outdoor reset, it's 70F when it's 70F outside and rises to the same 95F when it's 20F outside.
If you put those three lines together you get electricity usage for the year.
I'm reminded of a maxim that's often used when teaching someone something that requires a combination of talent and effort: "Talent is what you're given, effort is what you give." Except here, the first two lines are what you're given, the third line is where you have control. Your climate obviously is what it is. The performance curve of the heat pump is determined by the choice of equipment, once you've made that choice it's not really something you can change.
So the third curve is where the opportunity lies. Basically, the lower that line, the less electricity you will use. The blue line is a better line than the red line. There's two ways to lower that line. The first is to make sure that the outdoor reset curve matches as closely as possible your building, make that line as steep as it can be. The other is to have your radiators be as big as possible, so that you can use a lower water temperature across the board. That pulls the line down.
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Maxim for engineers - you can get 90% of the effect for 50% of the effort. I have seen "is the juice worth squeeze" used by some on this forum.
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The thing to keep in mind is that some juice costs more than other. Optimizing your outdoor reset curve costs nothing. Doubling the amount of radiation in the house? Well, that'll probably double the cost.
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