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.
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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.
Hey, I'm Dan from that video. I agree, its a bit too long but we don't script it out. They just point the camera at me for a half hour, let me babble and then they edit it down to 3-6 minutes. Its supposed to appeal to the non-technical...hence all the extra material.
This discussion was brought to my attention. I thought I would chime in, but by all means, feel free to ask any questions.
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.
There is some adjustment by the unit to changes in incoming air conditions, but remember that the evaporator(s) and condenser(s) are all in the same air stream. As incoming air temp/dewpoint drops, so does the evaporator temperature and the condenser temperature.
Its true that much of Quest's market is indoor ag, but many of them run 70F/50% during lights out, which is when the dehumidifiers are needed. At the end of the flower cycle, many growers want 65F/60% or lower. That's why the performance given on the Quest website goes from 60-80F and 40% to 60%.
Yep, you pretty much have it.
In this picture, the airflow goes left to right. The first coil is the pre-evaporator and the third coil is a condenser or recovery coil. The first coil's job is to get the air as close to the dewpoint as possible. The third coil's job is re-condense the refrigerant to a liquid before it goes through its second pressure drop. Coil 1 and 3 are at the same pressure/temperature. Essentially, coil 1 and 3 remove all the sensible heat necessary to bring the air down to the dewpoint without using any compressor energy. Very similar to the air to air heat exchanger.
Coil 2 is the low temperature evaporator. Much of the efficiency boost comes from the fact that it does not have to remove all that sensible. It can get straight to work on pulling out latent.
The second expansion device (dark grey in the picture) is a simple fixed orifice. The real control comes from the first expansion device (light grey). That will be a thermal or electronic expansion valve that is looking at the super heat leaving the evaporator (coil 2). This way the refrigerant pressure and mass flow is controlled to get as much as possible out of coil 1.
Of course the downside is that using a TXV to control across three coils means there's one heck of a time delay in larger units. EEV's help, but if you keep digging in the patents, you will find a more recent one where we solved this issue. That solution also gave us much better performance at low temperatures/dewpoints.
I should also mention the reason Quest units have 2 condensers for a total of 5 coils. There's no magic. It was an economic decision. In the R-410A versions, Coil 2 (evaporator) is a tube and fin evaporator. All of the other coils are microchannel heat exchangers...the exact same coil. In order to get enough heat rejection, we needed two condenser coils.
Why do this? When you only have two coils and one looks extremely different, its impossible to grab the wrong coil when assembling the unit. Imagine trying to build a machine with 5 different coils. Even the best person on our line would be sure to grab the wrong coil at some point.
If you look at Santa Fe's Oasis unit, it only has 4 coils because they only need one coil to be the condenser.
We have/had many different configurations that used the air to air heat exchanger over the last 20 years. The attached picture is the most popular configuration.
Why are we moving away from this?
1. People didn't like the way ductwork had to be attached. With the multi-coil configuration, its a straight through path for the air to follow.
2. Look at how many times that air had to change direction. It was a fair amount of pressure drop. It really limited our fan selection options. If there was a decrease in air flow, the performance/capacity of the unit would suffer.
The multi coils have barely any pressure drop. Plus, if there is a decrease in airflow it barely effects capacity. Its like slowing down air flow over an A/C coil...you get more latent removal because there is longer contact time and the air drops to a lower temperature. On most units, take away 1/3rd of the air flow and it only experiences a 3-7% reduction in capacity. The only issue is with the lower evaporator temperature, it could frost the coil and then the capacity would be effected negatively.
3. As mentioned, a lot of our customers are indoor ag. But we also have a lot of industrial customers and crawlspace applications that are dirty. Those heat exchangers could be cleaned, but not as easily as hosing down 4 or 5 coils.
4, Size is significantly reduced. Those heat exchangers take up a lot of space.
"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.
The old system of rating units to 80F/60% originated with the standard AHAM DH-1, but it has been superseded by the DOE regulation found in 10 CFR 430, specifically the test procedure found in appendix X1.
It creates two categories; portable and whole-home. Portable units are tested at 65F/60% and no external static pressure. Basically simulating a basement or crawlspace application. Whole-home units are tested at 73F/60% and 0.2" external static pressure to simulate a ducted system taking care of a home. These tests are the basis for both DOE's minimum energy efficiency requirements and EPA's Energy Star.
10 CFR 430 regulations and Energy Star only apply to consumer product dehumidifiers, which would be the Santa Fe brand. Quest units are considered industrial/agricultural. This means they are not subject to DOE and can not qualify for Energy Star. So you will never see a Quest unit with an Energy Star rating.
That said, there are several states that have minimum energy efficiency requirements for dehumidifiers used in indoor ag applications (aka cannabis). The most well known are the provisions in California's Title 24, which basically says that the dehumidifiers must meet the same efficiencies as those laid out by the DOE.
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.
You can think of Quest's multi-coil design as an active heat pipe. They have used heat pipes around cooling coils for some time, but there's no way to adjust the pressure. With the Quest design, the TXV is constantly looking at the leaving refrigerant conditions to adjust the pressure of the first and third coil.
Someone mentioned adding an outdoor condenser to reject heat. Quest did that. It was called the Cool 185...I'm sure its on the internet somewhere. It worked well, but there was no control over the amount of heat rejected. In the end, our customers wanted to keep their air conditioning and dehumidification separate, so the unit was discontinued.
Feel free to ask me any question. I set this one to send me an e-mail if there was a reply.
Thank you for your interest and comments. Dehumidifiers seem to be the outcast of the HVAC industry. Everyone seems to want to just cool the air and then throw in some electric strip heat to warm it back up. What a waste of energy. But its the least first cost.
Dan --
First, thanks for dropping in. I agree that dehumidifiers are the orphans, and I'm kind of a nerd so this is all exciting to me. I live and work in two very humid places, Washington, DC and Buzzard's Bay, where often the sensible heating load is not enough to get as much latent removal as I'd like. I just haven't been impressed with what is available so this is very exciting for me.
Here's a question: it seems like the effectiveness depends upon the target temperature. Going back to my post #17, "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." So is there either a way to adjust the target temperature, or even different models for different environments? Because it seems like a basement is a different environment from a grow room or even an attic.
Let me rephrase your question. Is there a difference between a dehumidifier optimized for a swimming pool (80F/60%) vs. a crawlspace (65F/60%)?
The simple answer is no. This is because the TXV is not trying to control that first coil to a specific temperature, it is operating to control the vapor leaving the evaporator to ~2-3F of superheat.
Let's say we have incoming air at 80F/60%/65F dewpoint. Optimally, coil 1 and 3 would be around 60F, which would cool the air just about to the dewpoint. Refrigerant boils in coil 1, condenses in coil 2, drops to a lower pressure and enters coil 3 (evaporator) where it all boils off and picks up just a little bit of superheat that is sensed by the TXV's bulb.
Now the air suddenly drops to 65F/60%/51F dewpoint. If coil 1 was still at 60F, almost nothing would happen to the refrigerant. The mostly liquid refrigerant would travel to coil 3 and then drop to coil 2 (evaporator). But now so much liquid refrigerant is dropping into coil 2 that it can't boil it all off, which means a liquid/vapor mixture without any superheat is leaving the evaporator. Now the TXV's bulb senses no more superheat and it tells the TXV to clamp down on the refrigerant flow. This flow reduction is accompanied by a larger pressure drop...which means the refrigerant flowing into Coil 1 is no longer 60F, its dropping to about 50F. Coil 1 now has a 15F difference between the refrigerant and the incoming air and it begins to boil. The balance is restored with air leaving coil 1 at about 53F and coil 2 doing most of the latent work.
There is nothing you need to do to adjust the unit to make this happen. It just senses the incoming conditions and adjusts.
In reality, there are things you can do to optimize for a particular set of conditions. If we knew for certain that a particular unit was going into a pool, a coil would be selected that could handle more condensed water since it will be in a hot/humid environment. If it was a colder space, a coil would be selected that did a better job defrosting. But when a dehumidifier leaves our factory, we have no idea where its going. So all are built to handle a wide range of conditions, though most are optimized around 70F/50%, which is perfect for human comfort and cannabis growing when the lights are out.
All this said, that is why the performance of these multicoil systems is often better than an air to air heat exchanger at lower temperatures. With a HX, you get what you get. With the multi coil, you can program it (especially EEV's) to push the first coil to a lower temperature or whatever gives you better performance.
So now this has me wondering, what does a TXV do? Because I don't know. I know it modulates the flow of refrigerant, and it looks at the pressure and temperature of the refrigerant leaving the coil. And if the temperature is low it reduces the flow, and if the pressure is high it reduces the flow. But beyond that I don't know. What is it trying to optimize? Anyone know?