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HRV in extreme desert heat?

Last Post 19 Sep 2018 01:07 AM by Dilettante. 13 Replies.

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MG1911

New Member

Posts:11

08 Sep 2018 05:32 PM
I am planning a "human refrigerator" in a desert environment where temps can reach 120F. This application will be off the grid. As I am conceiving it now (I am open to other suggestions), it will be a small (16x16), one-room building made of 12" SIPS for the floor, walls, and roof. It will have one door (no windows). It will be extremely airtight. It will be cooled with a small mini-split unit, powered by a generator. I am wondering if such a small, airtight space needs an HRV, but the HRV models I have looked at (Mitsubishi) specify in their technical manuals: "The outside air temperature SHALL BE 5F to 104F." Does this mean an ERV would not be effective in extreme heats such as 120F, or would be very inefficient? Is there another brand/model that would perform better, or should I consider a different design?

robinnc

Advanced Member

Posts:586

09 Sep 2018 06:16 AM
I am planning a "human refrigerator" in a desert environment where temps can reach 120F. This application will be off the grid. As I am conceiving it now (I am open to other suggestions), it will be a small (16x16), one-room building made of 12" SIPS for the floor, walls, and roof. It will have one door (no windows). It will be extremely airtight. It will be cooled with a small mini-split unit, powered by a generator. I am wondering if such a small, airtight space needs an HRV, but the HRV models I have looked at (Mitsubishi) specify in their technical manuals: "The outside air temperature SHALL BE 5F to 104F." Does this mean an ERV would not be effective in extreme heats such as 120F, or would be very inefficient? Is there another brand/model that would perform better, or should I consider a different design? WTTHFUCK".............I am planning a "human refrigerator" in a desert environment where temps can reach 120F. This application will be off the grid. As I am conceiving it now (I am open to other suggestions), it will be a small (16x16), one-room building made of 12" SIPS for the floor, walls, and roof. It will have one door (no windows). It will be extremely airtight. It will be cooled with a small mini-split unit, powered by a generator. I am wondering if such a small, airtight space needs an HRV, but the HRV models I have looked at (Mitsubishi) specify in their technical manuals: "The outside air temperature SHALL BE 5F to 104F." Does this mean an ERV would not be effective in extreme heats such as 120F, or would be very inefficient? Is there another brand/model that would perform better, or should I consider a different design?F ARE YOU ARE TALKING bout ???????????????

MG1911

New Member

Posts:11

09 Sep 2018 08:13 AM
Posted By robinnc on 09 Sep 2018 06:16 AM I am planning a "human refrigerator" in a desert environment where temps can reach 120F. This application will be off the grid. As I am conceiving it now (I am open to other suggestions), it will be a small (16x16), one-room building made of 12" SIPS for the floor, walls, and roof. It will have one door (no windows). It will be extremely airtight. It will be cooled with a small mini-split unit, powered by a generator. I am wondering if such a small, airtight space needs an HRV, but the HRV models I have looked at (Mitsubishi) specify in their technical manuals: "The outside air temperature SHALL BE 5F to 104F." Does this mean an ERV would not be effective in extreme heats such as 120F, or would be very inefficient? Is there another brand/model that would perform better, or should I consider a different design? WTTHFUCK".............I am planning a "human refrigerator" in a desert environment where temps can reach 120F. This application will be off the grid. As I am conceiving it now (I am open to other suggestions), it will be a small (16x16), one-room building made of 12" SIPS for the floor, walls, and roof. It will have one door (no windows). It will be extremely airtight. It will be cooled with a small mini-split unit, powered by a generator. I am wondering if such a small, airtight space needs an HRV, but the HRV models I have looked at (Mitsubishi) specify in their technical manuals: "The outside air temperature SHALL BE 5F to 104F." Does this mean an ERV would not be effective in extreme heats such as 120F, or would be very inefficient? Is there another brand/model that would perform better, or should I consider a different design?F ARE YOU ARE TALKING bout ??????????????? Hi robinnc, Maybe it would be helpful to just state the question without context: regarding their ERV systems, Mitsubishi specifies in their technical manuals that "the outside air temperature SHALL BE 5F to 104F." Does this mean their ERV would not be effective in extreme heats such as 120F, or would be very inefficient? If so, is there another brand/model that would perform better, or should I consider a different design (i.e., something other an ERV for such extreme heat environments)? Cheers, MG

arkie6

Veteran Member

Posts:1453

09 Sep 2018 03:58 PM
I don't know anything about your proposed HRV, but one thing you might investigate is an earth tube. Google for more info. Basically, it is just a tube buried in the ground which provides fresh air and brings the supply air temperature closer to the ground temperature. The deeper you bury the pipe and the longer the run, the closer you will get to earth temperature. Based on the small size of your space, I would think you could provide sufficient fresh air makeup with 4" thin wall PVC drain pipe. If you do this, I would use smooth wall rigid pipe with glued joints - not those long rolls of black corrugated stuff that collect stuff in the corrugations and offers more resistance to air flow . You would probably need 50' to 100' buried in the ground to get any appreciable drop in temperature. These can have problems in the east due to condensation buildup in the pipe, but if you are in the arid desert, this shouldn't be a concern.

newbostonconst User is Offline

Advanced Member

Posts:778

10 Sep 2018 11:59 AM
I don't see that spec or statement on Fantech brand HRV. I am guessing that the unit hasn't be tested at those temps or maybe it doesn't run as efficient at those temp so they but that exclusion statement. Or the motors burn up at those temps. Temps over 104 are common, I would choose another brand. So being that the AC unit is run off a generator and knowing generators are expensive to run continuously. Why not do solar on the roof? When the sun is shining is when you need to run the ac. Guessing HRV will also only run when the generator is running. Sounds like this is a portable place for workers to get out of the weather? Good Luck. Sounds like a cool little project.

"Never argue with an idiot. They will only bring you down to their level and beat you with experience." George Carlins

Dana1

Senior Member

Posts:6991

11 Sep 2018 07:49 PM
Posted By MG1911 on 08 Sep 2018 05:32 PM I am planning a "human refrigerator" in a desert environment where temps can reach 120F. This application will be off the grid. As I am conceiving it now (I am open to other suggestions), it will be a small (16x16), one-room building made of 12" SIPS for the floor, walls, and roof. It will have one door (no windows). It will be extremely airtight. It will be cooled with a small mini-split unit, powered by a generator. I am wondering if such a small, airtight space needs an HRV, but the HRV models I have looked at (Mitsubishi) specify in their technical manuals: "The outside air temperature SHALL BE 5F to 104F." Does this mean an ERV would not be effective in extreme heats such as 120F, or would be very inefficient? Is there another brand/model that would perform better, or should I consider a different design? Can you post a link to the literature where that temperature range is specified? At 300cfm even the smallest of the Lossnay series is ridiculously oversized for the ventilation needs of a "human refrigerator", unless you're packing a dozen or so humans at a time in that refrigerator. https://www.ecomfort.com/manuals/lossnaytech.pdf I suspect the humidity exchange efficiency won't meet spec at high temp, but even the best ERVs have very crummy humidity return compared to the sensible heat recovery. Overventilating even with a best-in-class ERV is going to add latent cooling load in a 120F swamp, and dessicate the refrigerator in an extremely dry (in absolute humidity dew point terms) desert. Have you considered a much smaller much lower power unit like the ceramic core Lunos e2 running at it's lowest ~10cfm speed? https://foursevenfive.com/content/product/ventilation/lunos_e2/spec_sheet_lunos_e2.pdf

MG1911

New Member

Posts:11

14 Sep 2018 09:40 PM
Hi newbostonconst, Solar would be an option, but to run an AC continuously in 120 degree weather (where it would still be very hot at night) would require a large (and expensive) solar array and battery bank, I believe. Generator power would probably be a more viable option. Hi Dana, Yes, that is technical manual I was referencing: https://www.ecomfort.com/manuals/lossnaytech.pdf Under Sec. 2 "Specifications" = "The outside air temperature SHALL BE 5F to 104F." Yes, we are talking about the desert, so outside humidity is not a factor under most circumstances, but I hadn't thought about the desiccating effect of the cooler inside air. I assume that is not a serious problem under most circumstances, or could be mitigated with some form of humidification.

Dana1

Senior Member

Posts:6991

14 Sep 2018 10:22 PM
It doesn't really matter what the temperature specs are for the Lossnay- it's LUDICROUSLY oversized cfm for a 256 square foot room even at it's minimum speed unless it's going to be the smoker's lounge with more than a half-dozen smoking occupants. Even for office type applications ASHRAE calls out 0.06 cfm per square foot (x 256= 15 cfm) plus 5cfm per occupant, and even that's higher than really needed. So for a single subject in the cooler you'd need AT MOST 20 cfm, for a couple of people, at most 25 cfm. For residential whole-house ventilation ASHRAE calls out 0.03 cfm per square foot (x 256' = 7.5cfm), plus 7.5 cfm per occupant, so for two you'd be at 22.5 cfm, but clearly overkill since that presumes minimal mixing in the home, and uneven ventilation. For a residential bedroom ASHRAE calls out 0.01cfm per square foot (x 256 = 2.6 cfm) , plus 7.5 cfm per occupant. (Building Science Corporation considers that more than adequate for whole-house ventilation, not just bedrooms.) That would be 17.5 cfm for a pair of sedentary/napping occupants, and even that is overkill given that it'll be very well mixed by the mini-split blower. For a tiny single room with active ventilation and a mini-split to mix it all up, forget the cfm per square foot- figure on 5-7.5 cfm per person. This Lunos e2 land, which delivers 22 cfm at high speed. That's good enough for four people unless they're doing something strenuous. If you need more due to higher occupancy than four people there are larger versions that can work that are FAR better suited to the application than a Lossnay. The smallest Lossnay would support the ventilation needs of a two dozen occupants doing aerobic exercises, which probably isn't what's happening in that refrigerator (is it?)

Dana1

Senior Member

Posts:6991

14 Sep 2018 10:22 PM
(deleted double-post)

Dana1

Senior Member

Posts:6991

14 Sep 2018 10:23 PM
It doesn't really matter what the temperature specs are for the Lossnay- it's LUDICROUSLY oversized cfm for a 256 square foot room even at it's minimum speed unless it's going to be the smoker's lounge with more than a half-dozen smoking occupants. Even for office type applications ASHRAE calls out 0.06 cfm per square foot (x 256= 15 cfm) plus 5cfm per occupant, and even that's higher than really needed. So for a single subject in the cooler you'd need AT MOST 20 cfm, for a couple of people, at most 25 cfm. For residential whole-house ventilation ASHRAE calls out 0.03 cfm per square foot (x 256' = 7.5cfm), plus 7.5 cfm per occupant, so for two you'd be at 22.5 cfm, but clearly overkill since that presumes minimal mixing in the home, and uneven ventilation. For a residential bedroom ASHRAE calls out 0.01cfm per square foot (x 256 = 2.6 cfm) , plus 7.5 cfm per occupant. (Building Science Corporation considers that more than adequate for whole-house ventilation, not just bedrooms.) That would be 17.5 cfm for a pair of sedentary/napping occupants, and even that is overkill given that it'll be very well mixed by the mini-split blower. For a tiny single room with active ventilation and a mini-split to mix it all up, forget the cfm per square foot- figure on 5-7.5 cfm per person. This Lunos e2 land, which delivers 22 cfm at high speed. That's good enough for four people unless they're doing something strenuous. If you need more due to higher occupancy than four people there are larger versions that can work that are FAR better suited to the application than a Lossnay. The smallest Lossnay would support the ventilation needs of two dozen occupants doing aerobic exercises, which probably isn't what's happening in that refrigerator (is it?)

MG1911

New Member

Posts:11

15 Sep 2018 01:52 AM
I just checked out the Lunos e2 you mentioned. Wow, I didn't even know such a thing existed. Looks very interesting, and appears to be a simpler, less intrusive install. Thanks.

Dilettante User is Offline

Advanced Member

Posts:503

16 Sep 2018 12:26 AM
Posted By MG1911 on 14 Sep 2018 09:40 PM Hi newbostonconst, Solar would be an option, but to run an AC continuously in 120 degree weather (where it would still be very hot at night) would require a large (and expensive) solar array and battery bank, I believe. Generator power would probably be a more viable option. Hi Dana, Yes, that is technical manual I was referencing: https://www.ecomfort.com/manuals/lossnaytech.pdf Under Sec. 2 "Specifications" = "The outside air temperature SHALL BE 5F to 104F." Yes, we are talking about the desert, so outside humidity is not a factor under most circumstances, but I hadn't thought about the desiccating effect of the cooler inside air. I assume that is not a serious problem under most circumstances, or could be mitigated with some form of humidification. The up-front cost may be higher. But tote up the amount of time the structure is going to be occupied. Now calculate how much fuel will be burned in that time by a constantly running generator. Multiply that by the cost of the fuel. Also factor in the costs of getting a new generator every so often as such an environment will eventually break the generator down. Now ammortize that against a 20-30 year panel+storage system. I think you'll find that such a system isn't really all THAT outrageously expensive. Additionally, if this is actually a "people refrigerator", and it's built, insulated and sealed properly, you shouldn't HAVE to run the AC continuously, even at 120 degrees. You're building with SIPs, 12", whole-home. So you're looking at something like an R-50-R70 whole-home envelope value. As long as the door is fairly airtight, you shouldn't have anything like insurmountable heat gain. Also, building codes may not allow you to get away without at least one window (fire regs). Simply build an overhang/awning for the window well. Mount it toward the interior, and install a sun shade. If you're fairly zealous about air sealing, it shouldn't be a problem.

Dana1

Senior Member

Posts:6991

18 Sep 2018 10:27 PM
Solar would make sense if the building is going to be used at a fairly high occupancy rate for several years, or if it is in a place so remote that the cost of shipping generator fuel is very high. If it's a temporary experimental installation seeing only intermittent use, probably not. High altitude or other remote mining operations install PV to offset diesel costs, but only if the mine will be needing that power for at least a half-dozen years. There may be rentable portable PV + battery options to consider, but I've never looked into it. An insulated door makes more sense for the alternate egress than windows, on both a cost and functional basis. Windows have significant solar gain from reflected light in bright desert locations even when there is no direct sun. A plain ~R4 steel exterior door would cost less to install than an egress sized window + shade and would outperform it (by a lot.)