Air to Water Heat Pumps for Radiant Heating And Cooling
Comments
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Luke this assumes there is much sensible cooling load left over after the FCU is done with dehumidifiying the air. In most places on the east coast, there is pretty much no sensible cooling left. In a lot of places even a low SHR coil setup is not enough to remove all the moisture without overcooling thus the ubiquitous dehumidifiers. Adding in the controls and complication for the radiant cooling gets you pretty nothing except a lot of cost.
I'm in pretty cold climate but with hut/muggy summers. I really wanted to make radiant cooling work as it would have saved an air handler on a reno I'm planning but it simply doesn't work.
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Luke,
You can always run the water temps at a higher point. But then in a humid environment, the output of the floors would be to low to do any real cooling. If a door opens or the dehumidification ever turns off then you will end up with a condensation problem. When doing radiant cooling and radiant fan coils it is always going to be a better design to have two different water temps.
The flow rate through the fan coils are to low for the radiant slab. Some water is going to have to bypass the fan coil. The fan coils will need to be piped before the radiant slab. Yes a system can be designed to do that.
The biggest problem you would have is the manufacturers warranty. I don't think any manufacturer will warranty a system unless it is installed to factory specs. A mixing valve and dewpoint sensor are required for that if you do radiant cooling by most Heat Pump manufacturers in a humid location..
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
The hyper heat Mitsubishi units are EVI, their marketing speak for the two stage compressors.
If you look at how EVI works, it uses some of the refrigerant to lower the temperature going to the outdoor coil. This refrigerant was already compressed once, so doing this does cost energy. It does significantly increase the temperature range as well as the max system output temperature so it is definitely a good thing in cold climate.
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You guys have to keep your minds open. Radiant cooling does work on the East Coast. Messana has been selling and installing radiant cooling into many homes on the East Coast. They have been doing it for decades now. I have radiant cooling in my own house installed back in 2007.
When you say things like it won't work, you close off your minds to learn something new.
https://radiantcooling.com
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
And to follow up on this thought, it's not like you can say to an air conditioner, "give me latent cooling only." Sensible cooling and latent cooling always go together, you can't get latent cooling without also doing sensible cooling. How much of each you get depends upon the temperature and humidity, and the temperature inside the air handler.
With conventional air conditioning there's a pretty good degree of self-regulation, the more humid it is inside, the more latent cooling you get. Let's say it's 77F inside your house and your air handler is at 50F. If the air is at 70% RH you get an SHR of 48%, if it's at 50% RH you get 72% and if it's at 30% RH you get 100%. So long as you have enough of a sensible load to get the thermostat to turn on you'll pretty much get the dehumidification you need.
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One of the things about humidity control is that humidity is really hard to model. Heat loss is easy, sensible gains are easy although solar can be tricky, but I'm not aware of any methodology for modeling humidity.
Counter to the folk wisdom, the hottest days aren't the most humid. At least around here, the most humid days are when it's not super hot. We had a day this summer when the dew point hit 77F: outdoor temperature of 78F, raining, outdoor humidity 99%.
If your thermostat is set at 77F, on a day like that your AC is hardly going to run at all. It's rainy out so there's hardly any solar gain, and the outdoor temp is right around the thermostat setpoint. There's almost zero sensible load, so the AC doesn't run. But the humidity is thick.
Hence the popularity of dehumidifiers. But the thing about dehumidifiers is they are quite efficient space heaters, they return to the space all of the latent heat that is extracted by removing humidity, in addition to the heat from the energy required to run them. So not only do they extract humidity, they also provide a sensible load that encourages the house AC to run more.
Now, from an energy perspective running a dehumidifier just so that you can run a 100% SHR cooling source like radiant cooling makes no sense. It's like leaving your windows open in the winter to get your radiant heat to run more so you can have toasty toes.
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Back 15 years ago the Europeans developed a new energy efficiency standard. They tested all the different HVAC equipment and put them into categories. The R and D happened with Eco-boiler.org who worked for the Euro Union. I called Belgium and found someone who spoke english that explained everything to me. Below is the results of the study done back then.
And below is a ATWHP with EVI that is now rated in the A+++ category. Europe is most definitely ahead of the USA with there energy standard.
That is a jump from the A and B categories to the A+++. It is a huge jump!!! Many ATWHP in Europe are in the A+++ category. You need to have an average yearly efficiency of over 300% or above a COP of 3 to be A+++ rated and be a electrical system. See how they rate electric resistance at 40% and not 100%. That is because they are applying a 2.5 conversion factor. 120 times 2.5=300.
EVI is a big reason for this huge jump in yearly average efficiency. That is huge!!!! Of course other ATWHP improvements could have contributed to this also.
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
I don’t like standards based on features and not performance. So I reject the European method. Moreover, what makes this different than air-to-air?
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Take a look at the COP graph bellow. Most EVI air to water units are similar. There is a drop in COP around 2C which is when vapor injection kicks in.
Most recent efficiency improvements have come from change to R32 or R290.
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Some R410A units are at A+++ too.
I dont see any specs on that unit from that website.
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
https://cdn.myshoptet.com/usr/www.spa-components.com/user/shop/big/1152-4_heat-pump-module-one-20-kw-monoblock.jpg
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I put together a sample of what I think is the most comprehensive way of looking at performance. It's based on the performance data for the Arctic 050ZA that you sent me, with the temperature distribution data for Washington, DC from NEEP.org.
It's based on a theoretical house with a 30,000 BTU/hr heating load at 22F, which is what NEEP has for the DC heating load.
For each degree of temperature I estimated heat pump capacity and COP. I assumed outdoor reset, water temperature of 95F at 5F and 86F at 44.6F. I just extrapolated from the full-load data give; NEEP has performance at minimum output which allows you to estimate part-load performance.
The model shows a weighted average COP of 4.6 for the heating season.
You can see it here:
usp=sharing
I hope it's self-explanatory, if not please ask.
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I do see a drop at 2c but look at -25c. That is -13f and the COP is above 1. Without EVI you won't even be running at -25c. At 20F COPs on EVI are higher than non evi at 20F. I don't understand the Mitsu tech. They may have developed something new that works in cold temps. It would be doing something similar to EVI just newer technology. Running a HP at 5f is going to use way more energy than 50F. At 51f and above my house doesn't even need any heat at all. My house is at warm weather shut down at 50F right now and my wife and kids aren't even aware this happens. They don't complain. So looking at a COP at 50f is mostly useless.
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
I'm with Kaos here. I spend an unnatural amount of time looking at heat pump performance curves. For the most part they're straight lines. I know the Mitsubishi vapor injection models have curves with a kink, it's really two lines depending on whether they're in vapor injection mode or not. This is true of both the capacity curve and the COP curve. In vapor injection mode the capacity curve is flatter, more capacity is retained. But the COP curve is steeper, COP suffers.
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DCContrarian,
Thanks for crunching the numbers on the HP. I will dive into some day when I get free time. My workload is high now going into heating season.
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0
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