Quest M-CoRR dehumidifier technology
Since we’ve had some fun talking about advanced dehumidifier technology recently, I thought people would interested in the four-refrigerant-coil design that Thermastor (parent company of Santa Fe) uses in their most efficient Quest branded dehumidifiers, which they call M-CoRR for Multi-Coil Refrigeration Recovery.
Their page on it, https://www.questclimate.com/m-corr-technology/, includes a 40 second animation that sort of explains it. There’s a fun youtube video that does explains it more thoroughly: https://www.youtube.com/watch?v=-vwjDABWk7M
They’ve also just released data on new models that use lower GWP refrigerants: R454B which has GWP = 466, which is 22% of the GWP = 2088 of R410A.
Some performance benchmarks: [edited to report numbers all at the same energy-star/DOE new standard conditions, 65 F, 60% RH]
Portable Energy Star requirement: 1.8 L/kWh
Compact whole-house Energy Star: 2.09 L/kWh
Energy Star for units in a larger box: 3.3 L/kWh
Best heat-exchanger based Santa Fe R454B unit: 2.81 L/kWh
Best R454B M-CoRR unit from Quest: 2.63 L/kWh
[or, at 80 F, those last two are 3.54 and 4 L/kWh–at higher temperatures, the M-CoRR design is better whereas at lower temperatures, the heat exch. design is better.]
It’s not actually that much more efficient than the heat-exchanger approach we discussed earlier this week [even at higher temperatures], but the approach is really clever:
The air flow path is across a mid-pressure evaporator to cool the air towards the dew point, and then across a low-pressure evaporator to drop moisture out of the air. That very cold air then goes across mid-pressure condensor that re-condenses the refrigerant before it goes through an expansion valve and into the low-pressure evaporator. Finally the air goes across a high-pressure condensor (not shown in the attached diagram) where the air takes up the extracted heat as sensible heat.
The cool think about this is that the refrigerant is evaporated and condensed twice even though it only goes through the compressor once. From that perspective it makes sense that you get about twice the L/kWh that you get from a regular two-coil dehumidifier.
You can also think of the function of it as being a different way to do the heat exchange that the Santa Fe does with an HRV-core type heat exchanger. And the results are similar in terms of L/kWh–the Quest products’ market positioning seems to be more as larger scale units for commercial applications. But where the capacity ranges of the two lines overlap, the M-CoRR approach does yield higher efficiency.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
So basically heat exchanger at the refrigerant level instead of the air level?
It seems like the high-pressure condenser could be either indoors or outdoors, depending on where you want to dump the extracted heat.
"There’s a fun youtube video that does explains it more thoroughly: https://www.youtube.com/watch?v=-vwjDABWk7M"
Six minute video, about 40 seconds of actual explanation. Why I generally hate YouTube.
Yup, I was just glad that there was a more complete explanation there than in on the web page.
This is all very interesting. What makes this -- or any heat pump -- work is that the boiling point of the refrigerant varies depending upon the pressure, so at the same temperature it can be either evaporating and absorbing heat or condensing and releasing heat, depending on the pressure.
If you look at the coils in the order that the refrigerant flows through them, it's 2 first, then 3 then 1. The air flows 1-2-3. So both the air and the refrigerant are flowing 2 to 3, but in coil 2 the refrigerant is evaporating and in coil 3 it is condensing. In order for that to happen the pressure has to be higher in coil 3 than in coil 2. That's kind of a neat trick if there isn't a pump between them because the flow is just driven by the entry pressure at coil 2.
Even if there is a pump between them it's still a neat trick.
Good explanation. One compressor, two expansion valves, and no other compressors or pumps.
I read their patent filing. (https://patents.google.com/patent/US10168058B2/en?oq=10%2c168%2c058 )
It says two valves, one is a TXV and one is a fixed orifice, they can go in either order. I'm still trying to wrap my head around how they get a pressure boost out of that.
OK, I got it figured out. I had i backwards, the refrigerant doesn't go 2-3-1, it's 1-3-2. So the refrigerant is going 3-2 and the air is going 2-3. So the refrigerant in coil 2 can be a lower pressure than coil 3, which means at the same temperature coil 2 can be cooling while coil 3 is warming.
Coils 1 and 3 are at the same pressure and the refrigerant has the same boiling point, probably around 60F. So air hits coil 1 at room temperature and the refrigerant boils and the air is cooled to 60F. Air hits coil 3 coming off coil 2 close to 32F, this causes the refrigerant to condense and the air warms to 60F. There's a valve between coils 3 and 2 which drops the pressure and hence drops the boiling point to around 32F.
The diagram on the patent application shows two metering valves, TXV's. One before coil 1 to keep it around 60F and one before coil 2 to keep it around 32F.
Still a neat trick.
Diagram is at: https://patentimages.storage.googleapis.com/d9/21/05/a67e8e9ee47709/US10168058-20190101-D00000.png
What I'm calling coil 1 is 340, coil 2 is 310, coil 3 is 320. The diagram shows two condenser coils, 330 and 350, although the text says 330 is optional and they're in series. I think that would allow for dumping some of the heat outdoors while keeping the exhaust at room temperature.
Efficiency is maximized when the the temperature (which is determined by the TXV) of coils 1 and 3 is such that the amount of heat removed by coil 1 is the same as the amount added by coil 3. If the dewpoint of the incoming air is lower than that temperature then it's just the midpoint between the temperature of coil 2 (around 32F) and room temperature. If the dewpoint is higher, some latent heat is extracted by coil 1 which means more sensible heat can be added by coil 3 and the exhaust temperature can be higher.
Efficiency is the exhaust temperature minus coil 2 temperature divided by room temperature minus coil 2 temperature. The more latent heat removed by coil 1, the higher the efficiency; if no latent heat is removed the efficiency is 50%.
Running some numbers through my dew point calculator it seems like efficiencies over about 60% would require extreme heat and humidity in the incoming air.
And unless you have a way of adjusting the TXV in response to conditions, you're going to have to make design assumptions and pick a temperature accordingly.
I think that's why the performance suffers at lower temperatures, these devices seem to be sold primarily to grow room operators who are running at high heat and humidity so their optimal coil temperature is higher than you'd typically see in a home.
By my calculation, with incoming air at 80F and 60% RH, the optimal TXV setting for coils 1 and 3 is 61F. With incoming air at 65F 60% RH, precooling to 61F does almost nothing.
Yes, when I first learned about these, I was seduced by the magic of using the refrigerant twice, but the heat exchange efficiency is actually more limited than with a large HRV type counterflow core. I guess that for the high capacity applications, they do the M-CoRR thing because the heat exchangers would be too large and expensive to get the combination of efficiency, flow rate, and static pressure drop they want.
Now that they are using the low GWP refrigerant, I think I want to buy one of the Santa Fe heat exch. models but I have to figure out where to install it. I'm thinking in my mechanical room with a duct connecting to the second floor above it so there's some whole-house circulation. Maybe with the intake on the upper level and supply to the lower level.
"the Quest products’ market positioning seems to be more as larger scale units for commercial applications. "
I did a brief search to see about pricing and availability. Every seller I found was in the hydroponics supply business.
They start around $2000 for the smallest units, which isn't too bad actually.
I found the 70 on sylvane (I think) for 1400
Looking at the Quest website, the 4.0 l/kWh seems to be at 80F/60%RH. The Energy Star ratings are at 65F/60% RH.
I don't see any numbers at the Energy Star spec.
Oh, thanks for catching that. I edited the original post to put in consistent numbers.
The 80/60 spec is the old one--that got changed five years ago and I hadn't updated my knowledge of it. I did find that Quest has a calculator page, linked below, where you get a performance estimate for any conditions. I found it pretty interesting: I think the model 105 is a discontinued air/air heat exchanger model, while the 335 and the 100 are a few of the higher performance M-CoRR models. It looks like the M-CoRR models drop in performance quite quickly at lower temperatures. I guess the multi-stage refrigerant system is tuned to work great in the higher temperature range, but would need things tweaked to work well at lower temperatures. So for residential applications, the heat exchanger approach seems to perform better.
https://calculator.questclimate.com/derated-calculator?state=eyJkZWh1bWlkaWZpZXJMaXN0IjpbeyJyb3dJZCI6MCwic2VsZWN0ZWREZWh1bWlkaWZpZXIiOiJRdWVzdCA3MCIsInRlbXBlcmF0dXJlIjo4MCwicmVsYXRpdmVIdW1pZGl0eSI6NjB9XSwidmlzaWJsZUNvbHVtbnMiOlsibW9kZWwiLCIiLCJ0ZW1wIiwicmgiLCJncHAiLCJjZm0iLCJwcGQiLCJsYmgiLCJwcGt3aHIiLCJhbXBzIiwibnYiLCJ0b3RhbEhlYXQiLCJsZWF2aW5nVGVtcCIsImxlYXZpbmdSaCIsImxlYXZpbmdHcmFpbnMiXX0%3D
See post #4. Indoor growers are going to tend to be warm.
In the discussion about air-to-air heat exchangers one of the things we talked about was applying it to hydronic cooling (ie chillers) to get better dehumidification. Obviously this technique depends upon the heat of vaporization of the refrigerant so it's not going to work with hydronics.
But it got me thinking. Back when solar thermal was a thing, one type of collector used a heat pipe, where fluid would boil in the collector and condense in a heat exchanger. If you had a fluid that boiled at about 55F could you do something similar in a dehumidifier? Air would enter at the bottom at room temperature, causing the fluid to boil and rise. Cold air exits at the top and hits the vapor, causing it to condense and warm the air. The fluid runs back down and the cycle repeats.
And if you can dream it, someone has probably already built it:
https://www.heatpipe.com/products/dhp-dehumidification-heat-pipes-series/
"Wrap around dehumidifier heat pipes are passive devices intended for use in air conditioning equipment to enhance dehumidification, reduce load on A/C equipment, and reduce or eliminate reheat. Each system is comprised of two modules; the first Heat Pipe module precools the entering air before it goes through the cooling coil. The precooled air then approaches the cooling coil at a lower temperature, thus lowering the load on the cooling coil or force a lower dew point. The cooling coil cools the air further before being reheated by the second Heat Pipe module. The function of the Heat Pipe is performed passively without any mechanical moving parts. The Heat Pipe is activated by the temperature difference between the air entering the precool Heat Pipe and the air leaving the cooling coil."
The ideal tech for this depends on whether you still want significant cooling and just want to shift the sensible/latent ratio, or whether you really want to minimize sensible cooling. I think the heat pipe is better when you don't need to achieve the extreme performance that a counterflow heat exch can approach. 50% heat exch "efficiency", while consuming no more electricity will give you a nice boost in latent, while you want 80+% if you really want to have very little sensible cooling.
The Quest patent drawing shows two stages of heat exchange with another condenser in the outflow path. If the alternative is dumping heat outside this only increases efficiency if it's warmer outside than the air coming out of the dehumidifier -- which is exactly the circumstances under which you'd want some sensible cooling anyway!
Similarly, you could do two stages of heat pipes. The first one would get a maximum of 50% heat recovery, the second one would get up to 50% of what remained, for a cumulative 75%. A third stage would get you to 87.5%, and so on and so on.