A/C question

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Old 08-06-08, 01:27 PM
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A/C question

This is for those A/C experts out there.

If you were to spray the outside unit (central A/C), the radiator looking part, with water. Would that effectively lower the temperature of air output from the air handler inside? I know this method is used on other similar applications and was wondering why it has not been widely implemented on central ac units.

If this would work, would there be any drawbacks (other than water consumption).

Thanks!
 
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Old 08-06-08, 01:30 PM
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Hard-water buildup on the fins would cause premature failure of the coil in many instances. The savings of electricity would not pay back having to by a new system before you got the full life out of the old one. JMI
 
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Old 08-06-08, 01:37 PM
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Muriatic Acid?

I'm kinda talking hypothetical here. There are solutions to most small problems like mineral buildup. I'm more concerned about the physics of it, if it really works.
 
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Old 08-06-08, 01:41 PM
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It will work to lower head pressure on the outdoor unit, using fewer amps to satisfy your thermostat during extreme hot days.....will it guarantee cooler air in the registers in the house, I don't believe that it would...I'm in the business, but not an engineer. Muriatic acid used on an annual basis would not be good for the coil either.
 
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Old 08-06-08, 01:46 PM
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I guess what i'm thinking is that if the water helps to cool the coils, then the liquid inside the coils will be cooler. Would that not equal cooler temps out of the register?

Oh yeah, for the hardwater problem, closed system using distilled water??
 
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Old 08-06-08, 02:02 PM
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This is the only example I'll cite...if you still want to put water on your condensor, I'd say go for it. A water cooled indoor condensor has water running through it's coils to control the head pressure. By running a consistent temperature, it uses less amperage on the compressor thus achieving a higher seer rating (more effeciency, not cooler air) that the same unit outdoors sitting in the sun. The air it makes is not any colder than the unit outdoors. The one outdoors just works a little harder. And yes, I've seen lime buildup in water cooled coils.
 
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Old 08-06-08, 02:06 PM
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Help me out here, what's head pressure?
 
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Old 08-06-08, 07:00 PM
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I'll take a shot at this without googling/dictionary/etc.:

Pressure can be read static(still) or dynamic(in motion). Static is when a line is filled under pressure and you hook up a gauge and take the measurement, say in psi, or water column(W.C.), with water.

But if it is in motion (dynamic), at the outflow of the pump(compressor in this case) you will create head pressure.

I can give you an example: Pumping water up to the roof of a 50 foot building's cooling tower. Down in the basement is the big water pump that has to pump it up there. 50 feet of water in a closed-loop water system, that has no outside (the system) pressure applied, may be about 20 psi, (based simply on water column pressure). Yet, if I were to put in a head pressure gauge just downstream of say the 10 hp circulation pump (compare to compressor), it might read 70, or some other lesser or higher figure based on GPM of flow (thus altering the head pressure).

Here is another way to envision this: Picture laying on your back with your legs in the air - bent. Now put a scale on your feet along with a weight on top of the scale. Say the weight is 50 pounds. Now slowly push up on the scale and the weight very slowly, and notice the scale reading probably will remain about what it was at static. But now, quickly thrust your legs(compressor or water pump driver) up and watch the reading on the scale (showing head pressure, due to dynamic force). The reading (50 pounds) will greatly increase with speed (75 pounds?, 100 pounds?, 200 pounds?, etc.), depending on the speed of lift.
 
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Old 08-06-08, 09:43 PM
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I do recall reading a thread similar to this awhile back. I believe the idea was largely dismissed due to what tinmantu mentioned - failure of the condensor coils prematurely.
 
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Old 08-07-08, 07:59 AM
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We used to have a cistern where water off the house roof is used for various things. Now, some use a huge barrel to store roof rain water.

This soft water could be used only when the temperature is very high. Also, condensate water form the A/C or dehumidifier(s) could be used.

The soft water mist does reduce condenser pressures & therefore temperatures. A lower condenser temp not only reduces its amp draw but also has BTUH capacity advantages.

For example from mfg'ers data; a 12-SEER 1.5-ton system at 75-F outdoor temp & 75-F indoor temp with 67-wet bulb yields 19,000-BTUH; at 115-F outdoor, same indoor conditions, with much more condenser amp draw, it produces only 15,900-BTUH.

Therefore, in some hot conditions above 100-F a soft-water mist could work, & save some on utility bills with little or no appreciable negative effects.

However, in most situations a soft-water mist would have little or no advantage. HVAC RETIRED
 
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Old 08-07-08, 09:43 AM
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So in other words, in the hotest parts of summer there might be a noticable increase in effieciency using spray/water.

Also if the condensate coming from the A coil is soft water, why would it not make sense to reroute that over the outside coils anyway?
 
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Old 08-07-08, 12:01 PM
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Spraying water on a hot condenser coil would help bring down the head (high side) operating pressure and temp due to the evaporative cooling of the coil. But at what cost? Void warranty, mineral buildup, possible electrolysis between dissimilar metals (copper and aluminum) in the presence of minerals (electrolytes) in the water, etc...
That said, I have used a fine water spray to cool refrigeration condensers in a pinch when the fan motor fails and it's critical the unit stay on line until a replacement fan can be found.
IIRC, someone came up with a water spray system for ACs back in the 70s and it didn't fly for most of the afore mentioned reasons.
 
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Old 08-07-08, 06:26 PM
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One idea that has been toyed with here and by others I'm sure, is to get free additional cooling if you have a cool basement in the 60's(temperature) - to use that as a geothermal source, and pull cool air directly through the blower in the furnace in the basement, and block off say a large central cold air return. To make this work, the right situations have to be present so that not all the cold goes unfelt by people in the residence, and simply gets wisked away to the basement to be recirculated.

I have an experiment going right now at an old lady's condo. She lives alone, no kids, no pets. She sits in a certain chair to watch tv. Her bedrooms are at one end of the place, and in theory the cold air could come out the open bedroom doors and come down the hall past the hall thermostat (which is a good thing) ,and continue towards her in the chair, before heading to the basement blower.

The large cold air return grill (at living room baseboard) temp that day was 71(which actually surprised me it was that cool) and at the stat 5 feet up was 75 1/2 (used one alcohol thermometer for both reads) with the a/c running steady that near 90 degree day. Then when I mostly blocked off the cold air enterning the furnace filter (by inserting the blower door down in the filter holder) and opened the blower and taped the filter in front of it there, the basement was 66 at that time. And a register temp. dropped from 61 (before) to 59 degrees(after).

However, we aleady know that the 66 degree basement air is not going to last. But, in theory by capturing cooler basement air, that will keep trying to come through the floor and walls down there, rather than recirculate upstairs air that is subject to the hot west sun and the attic above, it stands to reason that the cool air gain in the basement would always create additional cool to be added to the house, by allowing this to enter the blower directly.

Ontop of this, during the hot part of the day I am having her run the fan on fan "ON" setting (rather than "AUTO") so that between cycles, cooler air from the basement circulates, so in theory, the a/c compressor off-time increases it's off- time, by slowing down the rate of heat infiltration to the house.

As I said, this is an experiment - and this woman said she'd hunt me down if my theory somehow is flawed and her bill goes UP. I started this about 4 days ago and plan to go back and take some more temp readings there and also compare the a/c run times with some neighbors at this double 4-unit condo (8 units where they all have individual split systems). If I lived here I'd learn a lot more faster.

.....................

Sorry for my lengthy theory here, but this thread was reaching out to us with the goal of a way of getting addtitional cooling for free. I showed another possible way.
 
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Old 08-07-08, 07:07 PM
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Hopefully a mis-informed person won't take that test and run with it while having a gas fired water heater next to it and think it works so good they do this year round, and introducing CO into their home...sorry ecman, I just don't agree with the theory that you are trying.
 
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Old 08-07-08, 07:12 PM
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I will add, there is a reason why a home isn't cooling properly...just shooting a little "frezone" isn't the answer....all aspects of the system need to be analyzed by someone that is a professional and determine what the problem is. I don't mind giving info for basic stuff, but sometimes it goes above coming to a message board to save a buck. Not flaming ya bud, I like your posts but people running their systems with the blower doors off is not good advice, IMO.
 
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Old 08-07-08, 07:25 PM
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Originally Posted by tinmantu View Post
Hopefully a mis-informed person won't take that test and run with it while having a gas fired water heater next to it and think it works so good they do this year round, and introducing CO into their home...sorry ecman, I just don't agree with the theory that you are trying.
Good point and excellent on your toes thinking. No, it is electric and also the basement is a super clean poured walls basement, with no dampness/ mold issues or anything either.

If you want, you can PM me as to why you think this theory is no good. I am open to any thoughts.

Just thought I'd add also the blower door is sealed and the combustion chamber for furnace is the closed type, which helps.

This is a temporary experiment that is not going to go on for much longer. And I agree that if someone does not think of everything, like things you mentioned, there could be problems - and I should have thought of that before before perhaps posting this idea.

I also agree that systems need to be made to function properly as designed, but we also know that many good ideas get introduced to existing sytem theory. Geothermal, heat pumps, cooling systems that run cold water over coils, economizers, etc., were all thought of I'm sure after someone first discovered that blowing a fan across water or ice created a cooling effect. Point being: it may be possible to improve on that which is even engineered correctly, at the time.
 

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Old 08-07-08, 07:30 PM
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No need for pm's at this time...I'm mainly disagreeing because it wasn't clarified that it was an electric water heater....I've found that google is so fast that your post would be displayed in a search almost immediately. Just pointing out that someone that doesn't know what the consequences are, could have bad results from your theory. I look forward to talking to you more on here.
 
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Old 08-07-08, 07:52 PM
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I agree with your amendment, and yes in correct conditions of drawing basement air, it will help somewhat...only a summer of degree day temps compared to the previous years data would convince me there is that much of a savings. I just don't think taping a filter over the front of a furnace is the answer...btw, you aren't the first one to think of this, I took out an oldddddddd furnace last year where a 70 year old man had the same idea. Only he cut a hole in his blower door mounted a filter over it and ran it year round...Water heater right next to it....got called because CO detector was going off..he now has a nice new install and doesn't need a water sprinkler to keep his house cool.
 
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Old 08-07-08, 07:56 PM
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BTW, last post was for the sake of Google, not you necessarily
 
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Old 08-08-08, 07:56 AM
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My theory started with the condo straight across from her in the next building. Identical orientation and design. Both face the hot west sun. I was painting the place, with it vacant. It was stagnate and to the point I was thinking of turning on the a/c. It was 77 1/2 inside. I did the same alterations as my story, but did not run the a/c. Only put on the fan to run. The duct temp came down 3 degrees and stayed that way for hours, and the temp the next day, under identical outside weather conditions, was able to maintain 74.25 degrees, and between that temp and the feel of air movement in the house, it felt like the a/c was on! The boss came by and was so impressed he wanted to know if I coud do that at his house, because he said HIS basement temp is way cooler than this condos. He has gas appliances in the next basement room and are located about 16 feet away perhaps. He has not asked me any more about it, and I doubt he'll folow up on it.

BTW, after I left the condo, I put the furnace back the regular way before the new tenants came so they would not see and get ideas, per my boss's instructions. For one thing, they have a cat. Could you imagine a curious cat going inside the furnace?


But to maike it clear to other people and regarding your last story, this all is a classic case for where someone may know just enough to be dangerous. You can have gas applainces nearby (isn't there a 10 foot distance rule with cold air return and gas appliances?), or perhaps real musty basement air, or maybe volitile liquids stored down there, etc. At least where that single old lady is, all the conditions are as good as they can be.

But I want to close by saying any deviation from factory design can result in something one has not bargained for and sometimes can be dangerous.
 
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Old 08-08-08, 09:53 AM
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I understand where you're going with having the unit pull cooler air so it will be even cooler when it comes out. But isn't part of the job of the return to pull the warm air from up high so it gets cooled. Seems like there would't be good air circulation and thus inconsistent cooling if you just blew air into a room and didn't pull the hot out.
 
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Old 08-08-08, 07:54 PM
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It is pulling the hot out. Instead of into the big baseboard (low) cold air return, it is pulling it (low, also) down through the basement where then the room temp air mixes with cool basement air before going back through the cooling coils again. Think of the bottom of the basement stairs as the new cold air return location.

Keep in mind tht the entire house, including the basement is part of a closed system, that circulates, in a loop fashion. Your inquiry makes it sound as if it were now an open system, as if I introduced a vent to the outside, in the basement, and I was drawing air through the vent in the basement and bypassing the cold air return. Not so. As I said, it is still a closed system.
 
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Old 08-11-08, 08:37 AM
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So then you're leaving the basement door open to pull air from within the main floor? I'm not sure I understand what you're saying. It seems to me that if that is a closed system, by putting a return down in the basement without having a register down there, you'll actually be pulling cool air from upstairs as the return pulls the air out of the basement. It has to come from some where in a closed system, meaning air seeped from another area or through gaps in walls etc. I'm not saying it's a bad idea necessarily, just trying to figure out exactly what you're doing.
 
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