Outdoor mini split condenser unit in an insulated ventilated box indoors?
I need to cool (summer) and heat (winter) one room which is total 16.7 x 12.2 x 8.5 feet (1731 cubicfeet) (5.10m x 3.70m x 2.6m). I would need a unit between 2 or 3 tons.
Unfortunately I am not able to install the outside condenser unit outside of the building. That is the reason why I need expert advice.
I know the idea of putting an outdoor condenser unit inside was dismissed already but I was thinking to put the outdoor unit into an insulated box (inside one of my rooms). This insulated box would have two fans, which are each matched with the cfm rating of the condenser unit and pull air into and out of the box (from and to outside of the building).
I was looking at some of the mini splits and it seems that you can find outside units from mitsubishi which move around 2000 cfm.
I was thinking about using two fans like this ((https://www.ruck.eu/ventilatoren/rohrventilatoren1/rohrventilatoren-ec-motor/emix-ec/emix-355-ec-11?productFrequency=50&filterFrequency=50&filterErP=conform) which are each able to move around 2000 cfm.
Each fan uses at maximum load around 250 Watts of power. Considering a mini split has a COP rating of over 1, I think that even with the extra energy use of the fans I would come cheaper (energy wise) than anything else what would be possible in my place.
Can I build in another room an insulated box which contains the condenser unit and this box is connected to ducting which inputs air (from outside of building) and ducting which outputs air (also to outside of the building)? I know that the condenser needs big amounts of air, so I would install two fans which are each able to move around 2000 cfm of air. I would install one fan for pulling air from outside, pushing the air into the box and then another one pulling the air out of the box and pushing them outside. The fans were chosen under the assumption that most mitsubishi condenser units (in the range of power that I need) are able to move around 2000 cfm max each.
If I could use such a design, I would need to add 500 Watts total for the two fans. I think like that I would still be more energy efficient than other solutions. Maybe only one fan would also be sufficient, then I would only need 250 Watts extra. I am only able to use some indoor solutions and unfortunately geothermal pumps or swamp cooler are not possible. I know it is a bit problematic to find such device if you need a 2 to 3 ton unit.
So what do you know, would such a setup work? I have not enough knowledge and experience in HVAC, that is why I need to ask a pro.
So far I have some concerns:
– Are the outdoor condenser units working with variable fan speeds, and is it a problem if my inline fans blow directly onto the condenser unit? Maybe the airstream of the inline fans, messes with the heating or cooling process of the condenser unit. Also has fast moving air some sort of own effect in temperature (e.g. cooling through windchill)? If it would be the case that direct air has some detrimental effect on efficiency of the unit, I probably could use some sort of wind baffle like it is offered by Mitsubishi (https://www.pinterest.de/pin/469500329886926899). What do you think?
– I live in a climate where in winter we can get temperatures as cold as -5 Fahrenheit. It happens rarely but it can happen. That situation means that I would need a unit which would work also in these kind of temperatures. Mitsubishi offers Hyper Heating units which work in these temperature ranges. Unfortunately it seems that the Mitsubishi 2 to 3 ton units which support Hyper Heating are almost only twin systems (have two fans), which would mean a combined airflow of 3600cfm. To provide 3600cfm of air with my inline fans to the insulated box where the condenser unit would be in, I would need to buy much stronger and much more expensive inline fans. So I only know the Mitsubishi units so far, but maybe somebody of you know the product range of the other quality brands. Does somebody know a unit which is capable to work in low temperature settings and has a cfm rating of around 2000cfm? Other option would be if somebody knows strong inline or other fans which would be able to do 3600cfm and are actually not that expensive.
– also what do you think, would I need two or one of these inline fans? I mean suffice how much would such a condenser unit have postive influence on the static pressure. Would the outdoor unit be a resistance or an noticeable aid in pulling air for one fan in such a setup?
So that is the situation. I hope you can answer some of my questions. Thank you very much!
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Replies
The first question that comes to mind is how will you deal with the 5 or so gallons a day of water that will run out of the “outdoor “unit onto the floor of your building when in heat mode?
Did I miss this question in another thread?
Help me understand why this unit cannot find a spot outside the building to live but you can find room for two 36-48 inch square grills for your vent fans that are 12 feet apart?
If outdoor equipment is really impossible, then look at some of the water cooled options like this one.
http://www.daikinapplied.com/water-source-heat-pumps-enfinity-console.php
Walta
Is there no condensate drain? If there is, I just direct it somewhere else. e.g. outside. If not I place the unit on something where the condensate can drain.
Please no discussion about why I can't put the unit outside. The property owner does not want me to install a unit outside. But actually I have a lot of space inside which I can use.
Swamp cooler is also not possible as there is no water source in that building. If it would have been possible I would have done that right away.
I would need to know if my solution is technically possible or if there will arise big efficiency problems or other big problems when using the condenser unit with two matched inline fans and ducting. I don't have enough technical knowledge about these devices, so I need some well founded answer from you guys. Before I buy the stuff I need to be sure that it can be done.
How is it even possible that a ~200 square foot/~20 square meter room needs 2-3 tons of heating or cooling? Do you have a large amount of high-power equipment in that room or something? Even a tent that size wouldn't need 2 tons of compressor, even at -5F/-20C.
I suspect your heating and cooling load calculations are off (by quite a bit), and that the proposed solution is extreme overkill. Residential rooms that size could be heated/cooled by a 3/4 ton or 1-ton point terminal heat pump (PTHP) with integrated resistance heating auxiliary heat for when temperatures hit -20C, such as LG's LP093HD3B or LP123HD3B : http://www.lgptac.com/ptac-heat-pump.aspx/Download?filename=PAC-PB-FA-002-US_015G20.pdf&id=1317
There are many vendors of this type of equipment. Unlike a minisplit, the compressor and both coils are all in an integrated package that fits into a sleeve in wall.
Windchill is about the rate heat leaves human skin, and is irrelevant in a heating/cooling equipment context.
Where are you located (for climate data purposes)?
What type of construction, insulation, windows, etc are the exterior walls of this room?
I agree with Dana that PTHP sounds like the best solution. Here's a high-performance one to consider:
http://www.hotspotenergy.com/hotel-air-conditioner/
The indoor location with fan circulation could work, but it would be complicated to ensure you had adequate air circulation without excess power consumption.
If one PTHP isn't enough for some reason, two PTHPs would be the next thing to consider.
The units are made to be outdoors so no provisions are made to collect the water. Often draining in more than one location, so it will be up to you to collect and dispose of the water.
So the property owner is OK with you making large holes in his walls for your air ducts?
My guess is the owner will never approve the 12-18 square of hole in the wall you will need to move enough air for this idea to have any chance of working.
Did you ask about roof mounting the equipment?
Walta
Roof mounting and making new big holes in the wall is also not possible.
I got several thousand watts of computer equipment in that room. 2 tons is a minimum. I will recalculate later. But now I need to sort out the technical realisation of that issue.
The walls are brick walls and three of them are exterior walls. But these exterior walls have insulated plaster on each side of around 4 inches (each side). In winter when it freezes outside, then inside even without heating temperature doesn't drop as high as outdoors.
In the room I have two openings to the exterior in the size of 20"x14". Actually these openings are for ventilation. On this opening there was a huge box with an old fan inside, it was really heavy. I already removed it. One opening is directly connected to the outside and the other opening goes in an air chimney going straight up through the roof. This opening to the air chimney is the only opening the air chimney has.
So more to the realisation of the mini split in a box solution, please help me with that:
I realized that the fan of the outdoor unit of the mini split will operate at different speed RPM (revolutions per minute). This would mean that it would make sense to match my EC inline fans rpm with the rpm of the outdoor unit. The ec fans air volume output is a linear function of rpm and as it seems you control that by controlling voltage in the range of 0-10 Volts.
To match the rpm of the outdoor unit with the rpm of the inline fans, I would need to find out the rpm of the outdoor units fan. I was thinking by doing that by measuring the voltage of the fan of the outdoor unit. Then I would send that value to some controller which would calculate and then adjust the voltage setting for the inline fans. So that my inline fans would not work always on full speed what means that I could save power.
What do you think? Would that work? Or do you think it is better to measure Amps of the fan?
Actually I am also really wondering how fast the fan of the outdoor unit will usually run. I mean what determines its speed? I was trying to find some graphs which show the usual fan speed of such a unit over the course of a day, but couldn't find anything. I am wondering about that because I am trying to estimate the overall efficiency of my system. E.g. if the fan speed is linear with the overall power consumption of the compressor then I can calculate the energy efficiency rating for the whole system including my 500 Watts of inline fans. But if the fan speed of the outdoor unit is not linear with the compressor then I can't do that. Somehow I have the feeling that if the relation is not linear, the whole system would be less energy efficient because maybe the fan of the outdoor unit would often run fast when the compressor doesnt have much to do. that would cause my inline fans also to waste energy??? Maybe I am just thinking too much...
And considering the humidity problem. I might be able to build some sort of drain on the ground of the box. That wouldnt be so difficult. If the water would freeze then it would be more difficult.
Can you tell me if I make a box 1.5x1.5x1.5sqm, and if I match the inline fans rpm with the compressors fan rpm, if I will have trouble with air turbulences which disturb the operation of the compressor? I mean if I direct the first fans output at the air intake of the compressor and the intake of the other fan at the air output of the compressor, there should be a smooth airflow yes?
I did read about wind baffles, but I am not sure what they are for and why they enable to operate units at much lower temperatures. I understood it like that, that the wind baffles protect from snow, which would cause the units coils to freeze? But their purpose is not to protect from wind without snow?
My gut says you will not be able to move enough air thru a 14 x 20 opening too dissipate the heat from a 2 ton mini split.
Since it seems you only can use 1 usable opening for both intake and exhaust how will you keep them from mixing?
How many square feet of unconditioned space do you have inside the building? Maybe you could dump the heat inside?
Walta
This calls for an engineered solution, not a "design by web forum", or "hack and hope" solution.
I don't think even (multi-speed) fans that are NOT controlled directly by the mini-split will ever be an efficient (or even effective) solution.
I have two openings in the size of 14x20. One is at the air chimney and the other is at one of my walls. Both are made and have been used for ventilation. Both are independent. The fan in the link is rated for 2000 cfm with a round opening of 14 inch. So with 14x20 even more would be possible.
If I match the inline fans capacity with the compressors fan capacity then by logic it should work. I understand it like that, that the compressor can't handle more air than its maximal rated air flow capacity.
If I read out the mini splits fan voltage, I can calculate the appropriate voltage for my inline fans. So mini split fan and inline fans would run with sychronized rpm. So far I don't see a flaw in the logic. But I am not sure what that setup would do to the original EER or COP value of the unit. Do you know if the fan speed is linear correlated to the compressor load, or does it depen on other factors too?
Aren't there any good portable units which offer the option for ducting? So I could take one or two of these for cooling.
Like these units: http://www.americoolllc.com/products/wpc-7000
Do you know any other units like this? As I am based in Europe, I can't get these units.
Also I am not sure if I would need something for heating. Is there anything else than heat pumps which have a COP higher than 1? Are there any indoor heat pump configurations for heating? (e.g. with ducting?)
"What do you mean by an engineered solution?" Where do I get that? Can't I engineer my solution myself? ;-)
Here's what's claimed to be the most efficient portable air-conditioner.
http://www.climax-air.com/
You might need more than one.
As far as the mini-split setup, I think what I'd do is make a baffle that separates the room into a giant intake plenum and a giant exhaust plenum, with the mini-split outdoor unit mounted between them. Then I'd put in the two fans you have planned, and control them with feedback from a two channel manometer to force the pressure in each plenum to be equal to the outdoor air pressure (and equal to each other). That would guarantee that that mini-split would work as designed or better and would use no more fan energy than necessary.
Actually, I'd still use a PTHP in that setup, so that no refrigerant lines are needed.
Or take Charlie's idea and apply it to the box the condenser is in, separating the box into two halves with the condenser between them so the condenser's fan is drawing air in one side and out the other. 2000 CFM in a 14x20 duct is about 1100 FPM and about 0.1" static pressure per 100' of duct. If the total length was about half that, or 50', the fan in the condenser would only need to overcome about 0.05" of static pressure.
It might not be a perfect solution, but it would seem much simpler than trying to balance airflow with auxiliary fans. Also, if the airflow restriction did cause some reduced efficiency in the minisplit it would likely be less of a hit than running 500W worth of extra fans all the time.
Mini-split fans don't run at a single speed. They modulate the speed based on the compressor speed & load,, delta-Ts across the coil, etc. How do you intend to synchronize the external fan flow with the mini-split's fan?
I'm not suggesting that it's not a solvable problem, just not anywhere near as simple a problem as your proposed solution seems to indicate. Efficiency probably as important to you as effectiveness, but it's not simple arithmetic.
As far as I know, the only downside to over-ventilating a condensor is fan power draw. It happens naturally with outdoor units due to wind.
You could trigger and optionally modulate the fans by measuring pressures.
Wanting to heat a room full of computers makes no sense to me - it's normally all about cooling.
Hello I don’t know if you’ve solved your problem but I have seen a solution of installing a split mini AC Outdoor unit inside a insulated and vented utility closet
The video is about building an indoor grow operation with temperature reaching 110f
https://youtu.be/TwrOHWslLoc
I am considering the same type of installation
bicycle joe did you ever build your insulated closet with condenser inside like the youtube video? if so how did you do it? what were the dimensions and what size fans did you use?