Cooling Question

[lpipe]

I know this is a more mundane question, but judging from the out of the box thinking that I have witnessed on this forum, I have a question regarding the cooling of my house.

I am trying to find a way to reduce my dependence on my central A/C. The A/C is on its last leg and I would like to find a way to avoid the huge electric bills I have in the summer.

My house is in Houston, TX. Built in 1938 on a pier and beam foundation (meaning that it has a crawl space and no basement). The house is brick and is about 1500 square feet, one story with lots of windows and is north facing. I have two big live oak trees in front of the house, but no real protection from the sun on the south and west.

The air under the house is pretty cool even in the summer. I believe this house used to have a fan in the floor that drew the cool air up from under the house, but I can't find any information online about this kind of cooling.

Any ideas about how I can cool my house? I have a dehumidifier that I can run to take moisture out of the air, but that process produces heat.

I'm open to suggestions.

Thank you.

[FRC]

Geothermal, but it could be expensive to set up. Long term you would save.

FRC

[lpipe]

Geothermal, but it could be expensive to set up. Long term you would save.

FRC

I would love to have a geothermal, but you are right--too expensive and my house is on a small urban lot so there is no room for the equipment to drill the holes.

Builders are buying up little cottages like mine, tearing them down, and building huge houses, so I don't want to make a big investment. I'm really looking for something to tide me over for less than 5 years.

[mbrownn]

Evaporative cooling may be the answer.

This can be cheaply made using a fish tank water pump and a porous material of high surface area for the water to evaporate off.

It is very efficient in a dry atmosphere so if a small unit was placed on the output side of an aircon it can significantly improve the aircon efficiency. If placed on the input side it will work too but the efficiency is lower as the air is moister and the temperature gradient across the aircon unit is higher.

A drop in temperature of 3C below what the aircon is doing is easily achieved using this method, I have done it.

As it is combined with an aircon unit, the problems with extra moisture are not an issue as the aircon removes it.

To get the best results you need your evaporative media to be quite deep. Normal commercial units are only 2 to 3 inches, I would multiply this by 3 as a minimum.

I had a symphony evaporative cooler (cost more than an aircon) that my 5 year old broke by pouring water in the front causing the motor to burn out. I took the media from this and cut it into four pieces, placed it in a plastic box with openings at either end, it was about the size of a car battery. The fish tank pump was used to pump water from the bottom of the box to the top, wetting the media. Wow I had 3 degrees of cooling in 70% humidity.

This worked for quite a while until my son broke it, he is good at that.

[dutchdivco]

Maybe

I live in a place once; it was a real ****hole, but the rent was cheap; when summer came, I found out why.My utility bill was considerably more than the rent.After making sure the meter had been accurately read, and was working right, I complained to the landlord.He had an a/c guy come out, and put a new compreesor on it.But, the a/c guy said it probably wouldn't help.Said it was an old, and so very innefficient a/c unit. He was right, it didn't help, and I ended up moving out.So, a newer more efficient a/c unit may lower you bill, but upfront and payback wouldn't help, unless you culd get some kind of $ from utility or Gov't for going more energy efficient.Jim

[mbrownn]

Sorry to keep harping on about an aircon but after all it is the most common free energy device we have.

Typically it produces up to 10 times more heat on the hot side than you put into it so it is a very effective machine COP=10. The biggest problem with it is the more we need it, the lower the performance we get.

For example if it is 24C both inside and out but we want it 22C inside, our aircon will be around 50% efficient but give a COP of 10. This means it could produce a lot better results if it were more efficient in some way.

If the temperature was 30C and we wanted to make it 22 our efficiency would drop by a very small amount but our COP would drop significantly. Typically 49.9% efficient and a COP of 8, a 20% drop.

Why is this? The efficiency is effected by a fraction (around half) of the temperature difference as a percentage of the overall temperature in Kelvin. So at 24C we have 273+22=295. At 30C it is 273+30=303 you can see that the difference, 5C (or K) is only a tiny percentage of 303 and is not significant; however the temperature gradient has gone from 2C to 8C, four times as big. It is this that has caused the drop in COP.

By the way these figures are not exact. I made them up to show the principal but they are realistic.

Anything we do to reduce the temperature gradient on an aircon has a huge effect, actually it’s the same on a refrigerator too (a ref has a cop of around 2).

My evaporative cooler dropped the temperature by only 3C but reduced the temperature gradient by 3C too and it was this that dramatically reduced the compressor running time and therefore reduced my electricity bill significantly.

The truth is our temperature gradient on an aircon is the difference in temperature of the coils on the Freon circuit, so to make an aircon that will be very effective we need to alter that. The most effective way to do this is immerse the hot side in cool water, such as a stream. By doing this your COP goes through the roof even though your efficiency has hardly changed.

Typically the cold side might be 10C and the hot side 50C but by immersing the hot side in water at 20C we will change our gradient from 40 to 10C. Our COP could rise to fantastic levels making the need to run the compressor much less.

[WeThePeople]

I'm in Houston too, and the way I found was to find a cheap driller crew to dig a well for me, and drop a small 2" schedule-80 PVC casing to maintain the hole.

We have layer upon layer of aquafer below us, and dropping a substantial length of PEX 1/2" past the bottom as a heat exchanger is the answer for me.

Pull local drilling records to find which depths water wells are using and avoid them to be fair.

They are 200' with the last 20' screened NE of Houston as example,
but there is a 60' aquafer for us due to Lake Houston.

There is absolutely no way I can pump enough heat into the two 200' pieces of PEX I pushed into the well that will return even slightly warm water upon return.

I paid abour $22 per 100', so $44 total pipe cost,
and 120' are wasted in the well casing (60' X2).

So 80' of randomly exposed loop of PEX sinks any heat I send in.



People answering perhaps don't really understand just how humid Houston is,
so hayshakers and the likes just make things worse for most people's health.

I am using a very small 4000-BTU unit to cool a 46' x 46' building
because I disassembled the AC and carefully folded down the condensor.

It is submersed in a four gallon closed bath,
and the pump is a stainless steel gear type,
nothing to wear out expect seals.

It is only rated for 4.0-GPM flow rate.

the air is 38 degrees sustained from the custom freon mix I used,
but then again, I hardly expect people to go and do that...

I also replaced the freon pump with a two speed one.

Obviously, don't insulate the feed line to the well,
but do insulated the return line to keep Houston's heat out of it.

@mbrownn, sir, you have it right,
if you cannot vacate the heat efficiently,
your mostly throwing money at fire.

Stealth has a point too that I have tried,
but increasing the crawlspace temp hurt the main enviroment.

I drew air through the center of the building from the crawlspace
to the attic in a leftover piece of furnace ductwork with a good fan.

I (instead) elected to cover all the rafters in 1/4" panel,
and duct the eve's edges to the roof's peak instead.

I left a small triangle of space at the peak for a horizontal board
that formed the main exaust duct, and used three solar fans to
exhaust the roof's shingle heat directly back out to outside
before it ever gets into the attic in the first place.

From 145F to 92F is proof that concept works just fine,
and it is so inexpensive to do yourself too.

Yes, it helps in the winter too, without the condensation damage risks.