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Old 08-15-11, 07:24 PM   #1
launboy
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Default Two Simple A/C Improvement Ideas

So I had a light bulb moment just now. I'm not sure how much either of these would help but they both make sense and would be very easy to build. I myself will do both but I got all four wisdom teeth out this morning so I'm in recovery mode for now.

First idea is an air conditioner awning. Our Condenser is installed on the west side of our house and is in full sun from about noon on. It's also a design with no slatted sheet metal sides, just open coils that are black. To me there are two problems, one, sun is blaring on it all day, and two those black coils are just soaking up that extra heat.

Proposed idea is to get some light or white fabric and build a small awning off the west and south facing sides. This seems superior to most structures I've seen in that it won't cause recirculation issues like many things people build over their units. I figure the solar gain through the top of the a/c wont be that big of an issue because its painted light tan and is slatted sheemetal over the fan that does a pretty good job of keeping sun out.

Idea number two comes from evaporative cooling techniques. I've seen misting kits for sale for condensers but read they have issues with mineral build up when the water evaporates on the fins. Not only that, but a mister requires at least city water pressure to work correctly, which means your paying for the water to mist on it.

My idea however does not require city water pressure and as such can use many sources. Instead of misting the water infront of the coil and letting it get sucked through, I propose to run a small tube with many tiny holes in it around the top of the coil and let the water drip out and run down the fins.

This system could be gravity fed meaning you could use a rai water collection tank located higher then the unit, or better yet, use the condensate from the evaporator. My personal unit(in the basement) just drains via gravity into a floor drain, but many people have condensate pumps already in place that could be rerouted to pump the water into the container to be used. This has the added benefit that the water has a low mineral content due to it being condensed out of the air(I believe, correct me if I'm wrong on that) which would reduce fin build up. I'm not sure if condensate alone would be enough, but it could be supplemented with city water or a rain water system.

If this became a longterm solution a lead could be run from the low voltage side of the contactor to control another contactor and valve or possibly directly to a valve.

These are just ideas I thought of, feel free to correct, or improve on anything I said or just let me know what you all think

Adam

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Old 08-15-11, 07:44 PM   #2
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Damn! I have been thinking about using water on mine also. For the past couple of years I have had a plan in my head but have never brought it to fruition. Time to get it going.
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Old 08-15-11, 07:46 PM   #3
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My window a/c unit from 1990 uses both of those ideas, outside is light colored sheet metal and the water that collects us then boiled off on the outside coils.

What I have noticed tho is that A/C is better at drying the air then anything else and that dry air feels cool so why cool the air if you don't have to? in other words why are we putting a thermostat on A/C, why not a humidistat?
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Old 08-16-11, 12:47 AM   #4
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Quote:
Originally Posted by Ryland View Post
why are we putting a thermostat on A/C, why not a humidistat?
Brilliant!

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Old 08-16-11, 07:17 AM   #5
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I'd have to agree with Ryland. I experience exactly what he is talking about this summer. Two days in a row it was about 82F in my house. One day the humidity was 85% and the next it was down in the 60% range. The two days were completely different. The 85% day I was sitting there doing nothing and sweating with the ceiling fan on. The next I was pretty comfortable with the ceiling fan on. A humidistat sounds like a great addition. I know this is being used on at least some A/C units. The one my grandmother just got this year has a dehumidifier mode.
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Old 08-16-11, 08:18 AM   #6
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You can get whole house dehumidifiers that use much less energy than an AC unit does. I have also heard that some of them get power from hot water (I don't understand this yet) so if you have excess hot water in the summer form you solar panels you can put it to good use.
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Old 08-16-11, 08:45 AM   #7
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Got any links to those hot water dehumidifiers? Sounds interesting and would be a perfect use for the extra hot water I'll be producing with my panels in summer.
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Old 08-16-11, 10:25 AM   #8
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I'll try to find out. I had never heard of this kind of thing before but recently I heard the HVAC guy I go to telling a customer of mine about this. I haven't had the chance to talk to him about it yet though. I can't understand how it would work but he told them that they could run the dehumidifier with their 97% efficient Munchkin they use for radiant heat.

BTW that HVAC guy is a genius. Recently he told me that 18 years ago he built the geothermal heat pumps at the local co-op from air conditioners, AC_Hacker style. He said he could convert a minisplit to geothermal for me but I don't need to bother since the new ASHP's are going to eviscerate the geothermal market.
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Old 08-16-11, 03:21 PM   #9
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Quote:
Originally Posted by S-F View Post
He said he could convert a minisplit to geothermal for me but I don't need to bother since the new ASHP's are going to eviscerate the geothermal market.
He may be a genius, but I think he's been to too many sales presentations...

One of the biggest determiners of vapor-compression efficiency is the delta-T between the source temperature (ground temp or air temp) and the sink temperature (inside temp of house)... a lot of people refer to this as 'lift' or 'temperature lift'.

I came across a very interesting British study that compared ASHP and GSHP COP from various manufacturers (in the UK). Here are some relevant charts from that study:




It is a true marvel how much mini-split efficiency has improved, and I for one am enjoying that improvement. But all of the incremental efficiency improvements that are going into mini-splits can be equally applied to GSHPs.

In the end, GSHPs will always have the advantage of lower 'lift'.

If exceedingly good insulation practices were fiendishly followed, I can see that the onerous cost of earthwork could be reduced to the point where the cost of earthwork would become quite modest.

There's also the advantage that sheltering the compression equipment inside the house makes it last much longer.

Inverter technology is about to burst upon the scene of whole house ASHP units. I have already seen the sales literature. I have also seen reports from the UK of inverter technology being available to the GSHP installers there.

It is pretty standard already for whole house ASHPs to have ECM fans, but the real efficiency will come from ECM compressors (inverter tech).

BTW, I came across some really great "webinars" about GSHPs and radiant floors. I'll be posting links in a couple of days.

One of the things I did find out from the webinar is that the understanding that we generally display on this blog is actually ahead of the cutting edge of the industry... something to be proud of.

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Old 08-16-11, 04:05 PM   #10
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Quote:
Originally Posted by S-F View Post
You can get whole house dehumidifiers that use much less energy than an AC unit does. I have also heard that some of them get power from hot water (I don't understand this yet) so if you have excess hot water in the summer form you solar panels you can put it to good use.

I think I've already posted about this.?. But Recently I decided to use
the dehumidifier Mode on my Sanyo Mini-split.
It got super muggy, but wasn't really that hot, just very uncomfortable.
The inside coil got pretty cold, but the fan was hardly turning.
Just a small breeze of Very cold air coming out of it.
Outside, the drain hose was dripping pretty fast.
It wasn't too long before the house was very comfortable,
but a little bit on the cold side (for me anyways).
The TED was showing around 300 watts of power draw.
(That's 3 kwh after 10 hours, for a cost of 63 cents).

It seemed oddly low. Normal low cooling is 400-460w, even on a coolish day.

So, now we know how to use even less kwh per day, when it's not
real hot, but so damp, you feel like you're swimming..

The thing that I found interesting.. There is no humidity sensor on the Sanyo.
So, it just runs continuously. I never saw it shut down, until I increased
the temperature setpoint, well above room temp.
Nothing automatic when drying up the house. Just have to keep
an eye on how dry it's getting. Our house went from around 80%
down into the 40% range, IIRC..
It might have been 90% in here, since my Radio Shack digital
weather gadget is 10+ years old now..

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