Block sunlight from HVAC condensing unit
Paul_Z
| Posted in Energy, Heating & Insulation on
My HVAC condensing unit for my house gets continous direct sunlight for most of the day. If I were to build an awning overtop for the condensing unit to block the direct sunlight, would there be any energy savings, since the condensing unit would no longer be subjected to direct sun light.
I know that the awning would have to be placed high enough to not block the air circulation of the condensing unit
Replies
Say you get about 10 sq feet of 30 degree incident sunlight, that's 500 W * cosine factor * oxidized Alum coils, coeff of emmissivity is 0.15, condensor picks up only about 75 watts.
Say you have a 4T ac, AC is pulling 15 kW from the house. Small percentage, Helps some but not much, if you impede the air flow at all it may be a slight drag' on the system.
I have seen some devices that mist water on the outside unit. They claim big savings. Never seen one though.
devices that mist water on the outside unit
big versions of that are called cooling towers....<G>
I used a primitive version of that to pull our old AC unit through a hot summer. Set up an ag spray head to spray into the coil, turned the water on and off by hand. It worked amazingly well -- a compressor that could barely make the pipes chill suddenly could cool about 5 degrees an hour.I wouldn't want to do it long-term on a relatively new unit, of course -- it would almost certainly shorten the unit's life due to corrosion.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
Bad idea. Minerals in the water get left on the fins which reduces capacity which leads to more water which leads to more minerals left on the fins which leads to........
Bad idea. Minerals in the water get left on the fins which reduces capacity which leads to more water which leads to more minerals left on the fins which leads to........
An acid wash every few years is standard maintenance. It would take that long ato build up mineral deposits enough to bridge the coils and clog the fins.
Less of an issue of clogging fins is the reduced efficiency of the build up of the solids which dramatically changes the heat exchange properties. .... assuming the water has significant solids in it ... maybe some water supplies don't ... can't imagine that really (but I ain't no water expert).
Edited 7/8/2009 12:42 am ET by Clewless1
We kept a 150 ton condenser going one whole summer by setting sprinklers under it. In the design of that particular power plant the condensers were nearly under one of the coal belts. We washed the units twice a week durring the summer and it would still get ahead of us sometimes and shut down on high head pressure.
If we were not walking in coal dust we were mucking about in coal dust mud.
Yuk!
Glad I don't have to go to the power plants anymore.
I can sympathize with the coal dust. We used to have a briquet plant here, and the main ingrediant is coal. Glad I don't have to do any work there anymore.
Course, the cement plant ain't a whole lot better. Still not sure why the boiler is in the same room as the hoppers.
I've installed one with AMAZING results.A La Carte Government funding... the real democracy.
Me TOO!
i took the small plastic hose used for ice maker connections... wrapped it around the condenser.. and hooked it to a water supply with those little lawn sprinkler valves... i wired the vale to the thermostat so the water came on with the unit...
on the plastic line all it took was thumb tack holes placed where needed to make it put out a fine mist... we don't have water scale issues here...
cost maybe $20 and a few hours worked for years
on large flat roof we have misted the whole roof on really hot days... it really helped
p
Great if the water is distilled ... otherwise spraying water on the fins will result in a significant build up of deposits that will affect the efficiency. So while the concept is good and the increase in efficiency (short term) is good, this can't be a long term strategy ... otherwise we would see lots of systems using this concept since it is so simple and in many ways 'obvious'. The other guy is right ... this is the concept of a cooling tower ... for e.g. chilled water systems in big buildings ... they have special water treatment stuff going on with those systems. Maintenance is a big issue for those.
Where you do see the water cooled condenser idea is in window shakers where they splash condensate water up on the coils.
I don't think I said I did see such an animal. ??
>>they have special water treatment stuff going on with those systems. Maintenance is a big issue for those.
All of the cooling towers I have worked on have chemical treatment of the condenser water. If properly balanced the treatment will produce a soft scale that does not build up excessively on the cell media, or is easily washed off if it does. Maintenace is as simple as cleaning the scale sludge out of the sump, power washing the media, and back washing the the water ports in the top of the unit. All simple task that many building operators do not include in thier preventive maintenace programs.
Maybe one day someone will invent a trully idiot proof system that is self maintaining, but untill then it is a balancing act for the system owners. "Pay me now or pay me later" is what I tell them.
I would not reccomend a water spray system as a permanent solution for an air cooled condenser issue. It can be used as a stop gap measure to keep the system running untill condition improve enough do a proper cleaning of the coils.
We have a water cooled condenser unit as a back up system in our main telcom room. It is a flow through system that uses domestic water for the condeser supply and then dumps it into the sewer after it has done the job of heat exchange. We have also used the same type system in one of our pwer palnts where the environmental conditions have proven to to be to hostile for air cooled condenser units. They are more costly to operate due to increased domestic water use, but because they are self contained and located within the buildings, they have lasted many, many years longer than standard split systems or roof top units.
And why is it that so many of those water units are installed in the ceiling of the server room or equipment room?
I just love it when I get a call that there is a water leaking on the equipment.
Haven't run into that problem yet. Our Data Center has a raised panel floor and everything is under it. All the chilled water piping is under the floor and the Liebert AHU's supply air also discharges under the floor. We have a leek detection system in place that alerts us when we have any moisture there. Everything is a real PITA to work on under a floor like that, but at least we don't face the prospect of any of the server racks taking a shower.
Our water cooled condenser unit in our telecom room is just a back up unit. Unless we loose two 120 ton chillers or the cooling tower and a 40 ton air cooled scroll chiler the back up water/condenser unit never operates. Virtually everything in that area is on UPS and emergency circuits so even a power failure doesn't take us down.
It has taken seven years of upgradeing chillers, UPS, and generators for us to get to nearly a 99.9% fail safe system. That includes building another off site data center that is as reliable and suppose to be able to with stand a direct hit from and F-4 toronado. From a building maintenance and operations point we do everything possible to assure that we won't loose our system. Now if the hardware and software suppliers could do the same we could really lay claim to a true 99.9% reliabilty factor.
Look at
http://www.powermizers.com
http://www.alternative-heating-info.com click Alternative Cooling then click Water Cooled Air Conditioners
Just some info on the subject.
Ed Begley lives in Los Angeles where relative humidity runs 30% to 50% in summer. In fact, until cost of refrigeration AC's started coming down, many houses in hot dry areas used so-called swamp coolers that used evaporative cooling to both cool and humidify the air.I would guess that water misting would be of limited help in the eastern half of the country where humidity is high.BruceT
Very interesting indeed. Not sure about the mister style. Too simple, why hasn't this been done previously? Why isn't it standard on e.g. TRANE, Carrier, etc.?
The pic of the other one leaves me wondering ... where does the air flow into the unit? Good concept. Concerned about the water quality ... but maybe 'just' use a filter like the other one has.
I suspect both have some limitations that aren't revealed in the 'sales pitches' (although the 'chiller' style is not really a pitch).
Edited 7/9/2009 8:38 am ET by Clewless1
LA is running out of water as is most of the west. I am not sure this is an environmentally sound solution from that standpoint. You also have the problem that when scale builds up on the condenser coils efficiency goes down. There may be a few places where tap water is mineral free but not many.
Remember, the mist style system isn't really spraying water on the coil, just in the vicinity of the exterior. The intent is to cool the incoming air, not wet the coil. Course w/ the air flow inward, the coil will probably get wet, but it does have the filter .... Not sure, though. We're missing something here. There is some psychrometrics that we don't quite fully understand, I think that will affect this to some degree.
If everyone in LA used it ... yes ... water issues. Amazing how thermo affects stuff ... no free lunch, dudes. But in LA, much of the time (assuming 'good design', yeah right) you wouldn't need much cooling ... with the mild climate ... not hot like up here in the desert (Death Valley area).
Good Thoughts. I stumbled on units like this years ago looking for something else. I thought I would bring to alls attention. It is my understanding that some of these units only turn on after the outside temperature reaches a certain point. That way the condenser fins are not subject to the water all the time. The idea of a trip switch opining based upon the fan coming on was ingenious.
A compromise to an awning would be planting some type of shrubs around the unit. Keep them far enough away from it to not restrict the air flow into the coil. If tall enough, they will shade the unit except for periods when the sun is directly overhead.
Be sure to clean the condenser coils a couple of times durring the cooling season. Simply spraying them with something like 409 cleanser and rinsing works wonders. You would be surpized at the amount of grass clipping, bugs, dust , and other debris that gets sucked into the coils durring the course of the season. A good cleaning can lower the head pressure as much as 10 psi, and that helps your efficiency.
As others have said, regular cleaning will do you more good than shading.
Not that shading is bad, but for it to be most effective, it can't be just a sort of "umbrella" over the unit itself. The air temperature that the unit sees will still be extra hot because of the solar gain created by the side of the house and other nearby surfaces. That's why it's usually best to set the unit on the N or E side, if possible.
Cleaning of the indoor coil is good too, although it's not subject to the same degree of dirtying that the outdoor coil is.
"If I were to build an awning overtop for the condensing unit to block the direct sunlight, would there be any energy savings, since the condensing unit would no longer be subjected to direct sun light." No, not really.
When the unit is running, it pulls enough air through the coil that the minimal amount of heat from solar incidence in very insignificant. Your dealing with dry bulb air temperature to reject heat. What everyone said about the water spray gizmology is correct because then your dealing with wet bulb air temperatures.
I have a bush that hides and shades mine. I figured the shade would help and couldn't hurt.
You're right in that shade can't hurt, but if the bush that provide the shade restricts air flow, you'd be better off in full sun.
Not that close,couple feet.
In concept, this may be good. In practice, not sure if it is worth the hassle. With large volumes of convective air flow, not sure how much hotter than ambient the coil surfaces might get to make a difference. Remember, much of the surfaces are not exposed to direct sun just because the unit is sitting in the sun.
When I have my choice on where to locate it, I certainly choose a more shaded area, but to go out of your way to impose an architectural element over the unit ... hmmm don't think so. To make a bad location good may be too much work to make it worth it. Plant trees ... they reduce the load on the house, too and make the unit work less. And they sure are nice friends to have around!! Trees add value. Where are you located?