Most efficient way to dissipate heat from computer server and A/V racks
Hi! I am in the process of building a large home, 9000+ sq ft here in the SF Bay Area, where climate is very mild, and the HVAC is dominated by cooling load. We are using a S-series Mitsubishi VRF system with multiple indoor zones and the home will be quite tight and designed to be very efficient.
We have a full size basement, and one room will be a storage room that will also have 3 racks of computer equipment, which consumes about 2 KW of power more or less continuously. While we could put a small VRF indoor unit in that room to cool the computer equipment, I was thinking a more economical approach would be to vent the air from the top of 3 racks to the outside using a panasonic bathroom exhaust fan and balancing that with an equivalent panasonic whisperline inline fan blowing air from the normally cool outside into the base of the racks.
This would avoid having to deal with running the VRF system continuously, and the fans could speed up and down depending on temps in the equipment. The A/V amps from the house will be in the racks as well, so load can vary a bit.
The storage room has a wall on the side of a lightwell, so it’s easy to get ducting to the outside. I don’t mind if the storage room gets cooler than the rest of the house – if anything that would be a plus as it will help keep supplies down there fresher longer.
The climate here is not very humid, so I think there would not be a moisture concern, but wanted to get folks opinions on this option.
Any comments or suggestions would be super helpful to me!
Thanks,
Mike
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Mike, you have the benefit of very nice temperate outside air, so this could work for you. Here are some additional thoughts if you go this way:
Dirt!
Depending on where you are, outside air can be very dirty. Electronic equipment attracts dirt, your racks will be like an electrostatic air cleaner. You will want to do some filtering of that outside air, perhaps multiple stages.
For example, much of the original transmission equipment atop the 1st World Trade Center was cooled with heavy fans. Those fans were equipped with two stages of filters, pleated and bag. Wasn't enough, we still had issues with what I will call "micro-dirt", so when we replaced that gear in the '90s we went with air-conditioned rooms even though that was an additional expense.
Corrosion/Degradation
Site dependant, and likely better in California, but outside air often has "stuff" in it that causes corrosion and/or degradation. Edge connectors on circuit boards will corrode and rubber like insulation will degrade. It's an insidious problem that causes strange intermittent faults.
Out of Sight / Out of Mind
Depending on your owners, having a separate system may not be a good idea from an "Out of Sight / Out of Mind" perspective. If they are hot, they will call the HVAC repair person. If the equipment is hot due to a fan failure, "it" will need to call the HVAC repair person!
Mike,
Andrew clearly has more experience than I do on this issue, so it makes sense to listen to his advice.
One other point: On September 1, 2017, the temperature in San Francisco hit 106°F. It's possible that we'll see more days like that in the future due to global climate change.
On days like that, your 2,000-watt computer room will need something other than outdoor air to stay cool.
Mike,
I think your approach could work, but be aware that you are essentially creating an unbalanced, exhaust-only ventilation system. It may affect how your main ventilation system performs.
And you would probably want a jump duct to ensure that air could move into the equipment room from the rest of the house.
With so much equipment, I would install small ventilation fans on the individual racks to improve airflow. But I would not worry too much about the computers overheating and failing. Nowadays most devices don't seem to last more than two or three years before you start to have component failure in any case. The key issue is safeguarding the data. For that, a combination of RAID and offsite storage seems like the best option.
Interesting conundrum. What do the likes of Larry Page and Sergey Brin do in these instances?
No mention of a PV array, perhaps a very small minisplit and just add more capacity to the PV array?
Best data center practice is AC with racks in a cold aisle/hot aisle layout (improves AC efficiency). Set to 75-80F.
Intel had some success with outside air:
https://www.intel.com/content/dam/doc/technology-brief/data-center-efficiency-xeon-reducing-data-center-cost-with-air-economizer-brief.pdf
Thanks everyone. there is plenty of solar, but I am looking for the more efficient solution, and it just seems wrong to use a minisplit when outdoor air is sufficient cool enough to do the job with just a fan.
I do worry about interactions with the general building envelope and the main HVAC system. But my intent is to have it be balanced, with an exhaust fan pushing hot air out, and an intake fan. blowing air in at the bottom of the racks. It I can create a hot zone behind the racks that is ventilated in this manner, it seems like an efficient way to go.
Do you think it would be worth it to add diverters to switch from outside air to indoor air from a hallway to dump the heat into the basement to offset heating load? The climate here is cooling dominated, so maybe it's not worth it, but I always like to see waste recycled, even waste heat.
The Bay Area is not cooling dominated. The east bay is zone 3B, the rest is zone 3C. Even if your peak cooling loads are higher than peak heating load, the annual number of base 60F or base 65F HDD are still more than the annual CDD in zone 3C.
The average annual temperature in the east bay is almost exactly 65F, which makes it a perfectly balanced CDD=HDD climate at base 65F, and only very mildly tipped to cooling dominated using base 60F.
2000 watts is 6824 BTU/hr. A ~500 watt half-ton PTAC operating with a wall thermostat plus a ~500-600cfm fan operated off a thermostat in the basement would be the right solution here. A half-ton mini-split would be marginally more efficient, but at 3-5x the installed cost. Spending the cost difference on rooftop PV would be a better investment. The COP efficiency and capacity of an air conditioner is higher when the condenser coil is getting 65F or cooler air than when it's getting 95F air (the temperature at which air conditioner efficiency is tested.)
At an outdoor temperature of 65F (the average outdoor temperature, remember) and a server room temp of 75F, that's a 10F difference. A cubic foot of dry air is worth 0.018 BTU per degree-F, so to move 6824 BTU/hr of excess heat out takes 6824/(10F x 0.018)= 37,911 cubic feet per hour (/60=) 632 cfm.
Of course at 55F outdoors it takes half that, but at 55F outdoors it may not be needed at all, since there's probably more than 6824 BTU/hr of heat load in the adjacent conditioned spaces at that point, presenting less than a 6800 BTU/hr load to the cooling system. At 70F outdoor temp it needs twice the cfm, and the PTAC would likely have a higher COP.
An uninsulated 2x4 partition wall with half-inch wallboard on both sides has a U-factor of about U0.32 BTU/hr per square foot per degree F. So if it's 70F in the basement when it's 55F out, and 75F in the server room you have a 5F difference, and every 100 square feet of partition wall area is delivering U0.32 x 5F x 100'= 160 BTU/hr of heat into the basement. If the basement dwells at 65F every 100 square feet takes 300 BTU/hr off the cooling load. An open door or 200 cfm ventilation fan would buy you another 200cfm x 60 minutes x 0.018 x 10F= 2160 BTU/hr of heat transfer out of the room into the cooler part of the basement. A 600 cfm fan could move 6460 BTU/hr, or effectively all of the heat into a 65F basement, when the basement can take that much heat continuously without rising in temperature.
So, if if the circulation fan is operated off a heating thermostat set to heat the basement to 68-70F (if it can) using the waste heat from the server racks, and a PTAC cooling the storage room to 75-80F you're golden. The basement will take as much heat as it needs at a reasonable COP with the fan when there's an actual space heating load for the house, and the PTAC takes over as the heating load falls away, and the house's cooling load picks up. No diverters necessary, very little heat wasted. As the basement temps rise toward 70F the fan operates less, and the PTAC operates more.
Finding a 500-600cfm fan that's quiet enough is the next task. A Broan L500 probably fills the bill. At 0.1 water inches it's pulling 232 watts and delivering 520 cfm moving ~5600 BTU/hr at a delta-T of 10F, a COP of 7-ish (better than the VRF in heating mode), dropping to 3.5-ish (lower than the PTAC, and quite a bit lower than the VRF in heating mode) at a delta-T of 5F (=70F basement, 75F storage room). There may be more efficient Panasonic higher cfm units (or multiples) of comparable capacity to deliver better performance. A PAIR of FV-40VQ4 would about 780cfm for about the same power as the L500. I'm not sure if they have a bigger one.
Dana, thank you for your detailed input! Super helpful.
So are you are saying that the basement (which is almost 3000 sq ft) can basically absorb the heat from the servers easily, and reduce the heating load which will be needed to keep it comfortable because of losses to the earth around it?
So best to find a way of exhausting the heat into the rest of the basement than trying to exhaust it outside? Would taking a exhaust fan of the size you are describing and tying into the duct system that feeds the basement be a good idea? We have a City S-series VRF system, but most of the basement is fed by a ducted air handler indoor unit nearby the servers, so tying that in would be easy, and would dissipate the uniformly through the basement. Or what's the best way of distributing the heat to the rest of the basement?
It would be easy to exhaust the heat into the adjacent hallway, but I worry this would find it's way up through the stairway nearby, and heat up the top two floors instead of the basement.
Since we already have the VRF plumbing feeding multiple indoor units, rather than going the PTAC route, it might be cheaper to just use a wall mounted indoor unit behind the server racks, and set it to cool at 80 or 85 degrees for the times venting to the rest of the basement wasn't working. I can make sure the door to the storage room where the machines are has louvers or such for providing a pathway for air from the hallway, or do you think another approach would be better?
We usually keep the house at 68 in the winter, and maybe 72 the summer (we like things on the cooler side), but the basement area may be a bit cooler than the main part of the house in any case.
If I put one of the wall mounted indoor units there, should I mount it lower to the ground so it's directed at the base of the racks? Or should I get a small mini ducted unit and duct it directly into the bottom parts of the racks?
We should have plenty of solar power, but I would rather not have the main HVAC outdoor unit that would feed that server room be running all the time. Having the fan be on continuously or triggered by a thermostat would be easy to do. Maybe two fans? One that kicks in at one temp and the second that kicks in at a higher temp, and then the HVAC indoor unit of having both fans on isn't adequate?
When the VRF or the PTAC turns on, should the exhaust fans turn off?
Thanks!
HVAC for server rooms is speculated trade. If you just stick a mini split in there you run the risk that the air leaving the unit will come out below the dew point of the room so water will condense on the first surface it touches you do not want it to be your computer.
With that said I like the plan to spread the heat around the basement with a fan take a look at this DC variable speed fan with thermostatic control.
https://www.amazon.com/dp/B074XBXFPD/_encoding=UTF8?coliid=I2ZAA5LT7QRJYO&colid=2E8X1WMM906QT&psc=0
Walta
To know if or when the 3000' basement can take the full 2000 watts of heat of the server racks requires running a heat load calculation for the basement.
Mixing different air handlers and heat sources onto the same duct system is a complex design problem, not well suited for this type of hackery.
I have gotten a manual J, D and S done for the house. What parameters would tell me whether or not can take that load?
If tying into ductwork is a bad idea, what would you suggest in terms of how best to distribute the heat through the basement?
thanks!
3 Racks isn't huge, but that's a lot of U-space to fill and potentially a lot of heat that's generated. I don't know the layout of your space but this is what I would do:
To the exterior wall of the rack area I would make sure you *could* add a small minisplit (we cool, as needed, dozens of small IDFs this way - set it to 76 or whatever and leave it). So any pathways for condensate lines, power, etc).
Then I would build a room in a room with a hard lid. Put the door in front of the rack space so you can work easily and additional light and cooling can enter the room when you are working in the space.
Get whatever is appropriate from here and pull air from up high and pull in air down low: https://www.acinfinity.com/
Heat/cool the rest of the storage space as part of the regular conditioned space.
That's what I would start with, then add a cheap DIY minisplit if your temps just run too hot.
Check the Dedicated Home Theater section on AVSForum... a dozen guys have gone through what you are attempting to deal with. Often with massive amps and things that REALLY put out heat...
Sean, thanks for the very thoughtful reply. We are adding all the plumbing for a minisplit on the side of the room that the racks would be located in. That would be in addition to the lineset extensions from the large VRF system that is the primary heating and cooling for the house. Would that be in addition to any exhaust fans to move air out of the racks to a different room, or in place of those fans?
The room is primarily a storage room, so building a room with in a room that allows for access to the rack takes up a lot of space, esp because I have some 1U and 4U servers that pull out of the front of the rack quite a bit (30+ inches).
I could build a room in a room that that provided adequate space in the rear of the racks for access via a door on the side, but had the front of the racks open to the rest of the room. With rack filler plates to fill in any open rack units, I think the front of the racks could be pretty tight if I covered the perforations in the doors on the front. These racks are APC Netshelter VX racks with doors on the front and back, and solid side panels: http://www.apc.com/shop/us/en/products/NetShelter-VX-Seismic-42U-Enclosure-w-Sides-Black/P-AR2144BLK
I think I can put clear sealing plastic on the front door which would give a pretty good seal for air coming in from the front, but would still allow air coming up from the bottom of the rack to go up the front side of the servers and be exhausted out the back. Do you think that would be a good idea?
That acinfinity site is awesome, and gives me lots of ideas. Thanks for the pointer, though it seems more oriented around A/V than computers., I will have some big amps in one of the racks for whole house sound (fed by Chromecast Audio dongles), and some Home Theater gear for an nearby home theater area.
The main question is where to send the heat from the equipment once the layout is optimized for capturing the heat in a localized area. I could vent it to the rest of the basement, or exhaust it outside as I was originally planning, or try to cool it in place, though I think it would result in the minisplit running all the time. Do you have any advice about which approach you have seen work?
I love AVS forum, and have been looking at the dedicated home theater section, but not seen anything like this. Do you have specific threads I should look at?
PS Those cloudline duct fans on the acinfinity site seem much more ppwerful than the bath fans I have been looking at, and about as good as the best cfm/watt numbers I have seen for bath fans (I think the ECM fans may be better still though).
Thanks very much!
I see what you are saying regarding the space. The last thing you want is to have racked equipment that you can't access easily. If you have servers on rails and can't extend them fully you'll curse the situation every time you have to deal with it.
If the general storage space is part of the regular HVAC load, you could just run with it and see what the temps are and add the minisplit if needed (basically, don't overthink it - just see what the situation is after you are up and going).
We have lots of 10x10 or 10x12 data closets with perhaps some UPSs, large switches and occasionally servers - we often don't have anything cooling those. They just don't get hot. We have larger spaces with cooling coming up from the floor and all that, but those are true datacenters. Some newer construction closets will have minisplits (LG, Mits) with the remote control mounted on the wall and set at 75 or something and, frankly, I can't remember being in one of them when the minisplit is on even. Again, these have less going on then it seems like you might with 3 racks worth.
The ACInfinity cloudline looks promising to me. Especially with the probes and the control panels. They have some cool stuff. I hadn't posted here, but I was wondering if you could use those to distribute air from a central minisplit in a hallway to a couple bedrooms (i know that folks have done that with Panasonic bath fans wired to kick on when the minisplit is on).
Thanks for the pointer on avsforum. I did some searching and found a lot comments on the related problem of venting A/V racks. It does seem like venting hot air from the server racks into the RETURN air ducts seems to make the most sense. In the winter, this raises the temp of the supply air so the indoor air handler doesn't have to heat as much, and the summer, if the basement cooling turns on, then the hot air is sent into the cooling system. if it's off, it make push air through the basement through the return vents.
Does anyone see a problem with venting into the return ducts in this way?
The T10 duct fan can go all the way to 1101 CFM @170W and 39 dbm, seems like a bit of overkill. The T8 seems like a better size, but these are variable speed with temp control, so maybe not a bad idea to use a bigger than needed unit.
Making sure a minisplit can be installed there is this doesn't work seems like a good idea as well in case the venting doesn't work. It will take a bit to try and build the racks and walls so the hotzone can be formed behind the racks, but seems like it's doable.
thanks everyone
Hi Mike, I am a thermal engineer and mostly work in the electronics cooling industry. I usually concentrate at the device and board level, not at the room level, but if this were my house I would absolutely seal the room and install a 9k BTU hyper heat mini split.
The electronics will have a longer MTBF if the room temp is kept constant, humidity is controlled, and dust/dirt is eliminated. Considering the size of the house a $1700 mini split cost would be a rounding error.
I know it may be attractive to pump in outside air if it is cool out, but that is just asking for a host of issues with your expensive electronics. Also, if it is cool outside great, the COP of the hyper heat will be extremely high, perhaps over 10!
https://www.nrel.gov/docs/fy11osti/52175.pdf
You could install two ducted mini-splits and for one of them, put the "outdoor" unit in the basement.
This maintains a sealed room (no dust), makes use of the ~$200/mo of waste heat and still allows the extra efficiency of cold/hot separation (yes, hot air should go to the AC return).
If slightly less reliability from dust and temp variation isn't a concern, then inside air when it's cold or very hot and otherwise outdoor air sounds pretty good.
Might as well use the heat to your benefit, give it to a heat pump water heater.
We have gas for hot water heating. But I don't understand how a heat pump water heater fits in to the server heat dissipation question? How do you blow hot air into a water heater???
@ Mike Myers: Put the water heater in the same room as the electronics racks and it's a done deal. Some heat pump water heaters have ducted options that would do the same thing from the other side of the partition wall to electronics racks.
I looked up the specs on heat pump water heaters. Very cool - I had never heard of them before.
Also, if it was running, how much cooling would it actually provide? That is, if I had a high CFM duct fan blowing into the water heater heat pump assembly, would it be reliable enough to cool the system, even when hot water demand varied a lot through the day?
Also, it looks like the units available aren't big enough to make sure the house has endless hot water at peak hour, at least for not a house of this size.
If there was a way to provide gas assist in the peak hour to never run out of hot water, but make sure the cooling provided was also adequate, this could be a real winner. I have never heard anyone do anything like this before. If it did work, I'd definitely write this up.
I thought the heat pump water heater idea was masterful!
Wasn't worried about you not having enough hot water though. Rather I wondered what would happen if you went away for the weekend and didn't use any hot water. Ostensibly you might not have enough cooling in that room then.
BTW, back to thinking about having enough hot water, the question I pose to those who have a heat pump water heater, what is the max temp it makes? Can it make 150 degree water that you could then meter out using a downstream mix valve? That would extend how much hot water the household had available. (That's basically what I do off my geothermal desuperheater, make 150 degree water and then use a mix valve to get it to safe temperatures.)
The amount of sensible cooling the water heater provides depends on how much hot water you use. In a 75F room about 2/3 or more of the heat going into the water comes from the room air. It's not going to be the total solution, but it'll be doing something other than throwing that heat outside.
And no, a heat pump water heater will never provide "endless shower" service, even with a fairly big one.
I'm not sure what the maximum storage temperature is on a given model, but codes require that water heaters be capable of storage temps of at least 140F, and that it be tempered to 120F or lower prior to any hot water distribution plumbing that goes to a sink, or bath. Use of un-tempered water is allowed for dish washers & clothes washers.
No matter how you're heating hot water, if there is going to be significant shower use, a drainwater heat exchanger cut the energy use for shower by half or more with a 4" x 48" or bigger drainwater heat exchanger downstream of the shower drain.
I have one (GE geospring 50 gallon) in an open 1850 sf conditioned basement. I have mine set at 135 which is the recommended set point per manual, not sure of max set point. I keep mine in hybrid mode, if you needed more heat removal and didnt need full capacity or recovery you could keep it in full heat pump mode.
Like Andrew mentioned when you're off on vacation you would probably need a plan B unless you're able to power some equipment down. If you'd like any more info I'd be happy to try and help you out.
I dont know how inefficient this is, but Ive noticed rack rooms using a window mount A/C cut in the wall piped to a floor drain at more than one apartment property.
I can't find any data on these heat pump water heaters on how much they lower the temp of air and what the sweet spot for their efficiency is- for some reason they are not speced as air conditioners. :)
The Rheem units can be fed with ducted intake and exhaust. I could run the exhaust the server racks through it and have it vent to the rest of the basement via the mechanical room, or into the intake of the basement air handler which is also in the mechanical room. They are not next door to each other, but not that far away that I couldn't run a duct.
However, the duct size on the Rheem is not that large, and would probably be a constraint on an 8" duct from the server racks.
Another question would be how to plumb this with a gas heater? If this was primary heat, I guess it could run into a tankless style unit as it's input, and as the heat pump tank drained and water temps started to fall, the tankless unit would kick in and heat the water up to target temp. If it was powerful enough, it would carry the whole house's load.
I guess it could be plumbed the other way, where the heatpump heater acted as a backup to gas, but then it wouldn't be on very much, so wouldn't cool that much and then what's the point of doing all the complicated plumbing.
Of course, one would have to be able to do the tradeoff calculations on electric heat vs gas heat and what 75-80 degree air would help the heat pump over say 65 degree air. I don't know that there is any way to do that math with the data available.
Mike, if you Google "GEOTHERMAL DESUPERHEATER PRE-HEAT TANK" and then click on "Images" you will find examples of how this is often done with two tanks. In your case the heat pump water heater would replace the geo unit and first tank.
(The two tank method is not the way we did it at my house, we used a one tank method. Sometimes I wish we had gone with the two tank method though.)
I I found this article from Matt Risinger which was pretty informative: http://mattrisinger.com/rheems-hybrid-heat-pump-water-heater-gets-an-update-hb50rh-prestige-review/
The hot water heater provides 3/4 ton of cooling! Of course, it doesn't run that often, and is probably not rated for continuous operation. But I see the appeal of recycling the waste heat in this way.
The ducts on the rheem are only 4", so not a good idea to run an 8" fan duct to that.
Im surprised Rheem is only 4" considering these things need to move air to work.
Bradford White bought GE's HPWH division and have Bradford White Aerotherm which is just rebadged GE, at least on the surface its identical to my GE Geospring other than the different color cap. The intake and exhaust hood adapters are 8" on their units.
When I took a peek at it with my thermal camera not too long ago I was getting 55F temp reading of the grille.
So to update folks here, based on the feedback on this thread, I started talking to the HVAC contractor about tying the server rack fans into the return venting, and also wanted to get more info on the make up air plan and if there was a way to integrate the cooling into that system.
I don't think I was obnoxious at all, but the HVAC company fired us as customers. They apparently have had "bad experiences" with howeowners that have tried to educate themselves and have non-standard configurations. Granted, we had a Mitsubishi VRF system designed based on the manual J, D and S studies that were done (I gather these are not done that often for high end homes in this area).
So my GC is now going down his list of good HVAC firms he's worked with in the past who are willing to deal with a VRF system and a homeowner who is an engineer that likes to study up on topics. :)
It's not the gating factor in the schedule yet, but will be in another months or so.
This was a firm that does commercial as well as residential, so I would be suroprised if the VRF system was uncommon for them. Is this sort of reaction common in the business?
thanks!
I can't really fault the contractor from bailing on this one. They can end up spending a whole lot of time designing then re-designing a client's hack, and still end up with something that the client isn't satisfied with.
Whenever I do the preliminary design on something out of the ordinary and throw it over the transom at a contractor, I've been explicit about what I want, and offer to sign a performance waiver to relieve them of the responsibility if it doesn't work out as expected, leaving them only on the hook for their work, not the system design. And I don't keep going back & forth with them for re-design or design tweaks. It's not their job to play tutor to aspiring Jr. HVAC designers- there are professional educators (charging real money) for that.
Dana, thanks for your input. What is best way to communicate the things we have discussed in this thread to an HVAC contractor? I did ask because the folks I was dealing with didn't have a good idea on how to deal with server cooling efficiently, and that's the reason I posted here in the first place. :)
Milo:
I feel for you with the contractor issues. I am in NC in a similar hot market. What amazes me is that many of the HVAC companies won't even do residential new construction work anymore. They just say no. Service calls are much more profitable. I wonder how the companies like Carrier etc. feel about their certified installers refusing to do installs??
It seems most HVAC contractors do not want to install mini split system they will do their very best to talk you out of installing one, if you insist on a quote it will have an I do not want this job pricing. If you should accept the bid I can see them looking for a reasons to quit the job.
If you look at it from there point of view. They have lots of experience installing over sized equipment with leaky ductwork on the attic and if it is a big house then the answer is to add second oversized leaky system. They know how to bid this system and turn a profit and the customer never call and complain that the home is hot in the summer or cold in the winter. So from their point of view the systems are perfect. The operating costs are irrelevant to them.
Try finding the HVAC distributor let them know you are not looking bypass the contractor. That you want a contractor with experience installing mini split system and ask them who has been buying mini splits. They will have a policy of not recommending any one contractor over others. Let them know you are not asking for recommendations, just sales data you do not want or need numbers.
Walta