A coil dehumidification

Karl_Northwind

So in the last heat wave, My wife and I have been dreaming of dehumidification and possibly air conditioning. 

Our house is smallish, superinsulated, in the country and on a well.  We have radiant heating all around, so no central AC.



I have had thoughts about running an old furnace with an A coil on top with domestic water running thru the A coil at a low flow rate to cool and dehumidify the air stream.  I can get ducts up below the stairs, and send the air out below the top step.  The return would be below the bottom steps and under the kitchen cabinets.



I'd have to run the water down the drain (sump line to the field, or into the rainwater tank I use for irrigation/watering.  Fortunately, hot weather here usually means we're watering the garden and orchards, and rainwater has been lacking here this summer after an epically wet spring. 



can anyone give me some assistance with assessing the effectiveness of this option? 

we have no shortage of water, which will get reused anyway. 

the typical heat and humidity we have been seeing here is about 84F and 80%RH in the house, and 90F and 70%RH outside.  Ground water temp here is about 50F.



Even if I can drop the inside humidity 10% and 10 degrees it'll be much more tolerable.

I'm willing to use a couple of window units if necessary, but this seems like a fun option.

Thanks

Karl

meplumber

Some issues.

What you are describing is called a "pump and dump" system.  There is some research taking place by the drinking water folks about contamination of the domestic water supply by these systems.  They are not being recommended at this time.



I have used ductless mini splits in conjunction with radiant heat with excellent success for quite some time.  There is no duct required.  By utilizing a heat pump, you would be able to heat the space on chilly fall and spring mornings without bringing the radiant all the way up to temp.  You get dehumidification and a/c in a very efficient package.  I am partial to the Fujitsu's but the others are great as well.



Good Luck.

Karl_Northwind

pump and dump

I understand the contamination issues, and plan to feed it thru a double check valve like the radiant system, and dump it with an air gap into my watering tank (non potable rainwater anyway)

I would love a couple of minisplits. but the budget isn't there.  I can get this stuff for free.

K

Mark Eatherton

Bob Gagnon has done this...

In fact, if I'm not mistaken, he has a water bed that is being cooled by the same system. Or at least DID have at one point in time.



I am sure it would help. Not sure how you'd predict its performance, but if its free, it has to be worth the effort.



So long as its operation is based upon the natural need for irrigation water, personally I'd have no problems (environmentally) with it. But if you have to use water to make it work, and don't have a need for the discharge, I'd raise my eye brow. But knowing what I know about your environmental responsibility, I don't see you doing something that would waste any resource.



There are some non mechanical de-humidification (desicant) systems out there that if the home is fairly tight, might assist in lowering the rH.



http://en.wikipedia.org/wiki/Dehumidifier



Travel responsibly out there...



ME

Ironman

A Viable Consideration

A company that I worked for about 35 years ago had an old theater in Alexandria, Va. on contract that had this type of system. The theater was located about a block from the Potomac river and the system pulled water from a deep well below the river. If memory serves me correctly, it ran a constant 48* water temp through a large chilled water coil in an AHU. It seemed to work sufficiently, all things considered. I can't recall the size of the system or the pump that served it, but it had to have been large.



That to me is one of the main issues: the size and amp draw of the pump. If you're pulling alot of amps per ton, then you might be better off as far as usage goes with an inverter driven mini-split. However, there are smart pumps available for open loops that use substantially less current, but are of course more $$$ up front.



For a chilled water coil, we normally would like to see 2.5 - 3 gpm, per ton at a supply temp of 44* and a 10* Delta T, max. This would be with the normal air flow of 400 cfm per ton. With your water temp at 50*, you would obviously need to over size the coil and lower your cfm/ton. This is of course designing for ideal conditions and you may be content with less.



Another thing that you may want to consider is using a chilled water convector(s) instead of a ducted system. If that's not feasible, then I'd recommend using a chilled water AHU rather than an old furnace and a chilled water "A" coil. ADP and First Co. have these with ecm or fixed speed available.



I like the idea you're considering and it's something that I've given some thought to at my own place. We're on well with a virtually unlimited water table. The county has a pump house in a field about 300 yards from us that pulls about 1500 gpm and that doesn't even knock a dent in what's available.



You may want to post this over on the HVAC forum and let Prof. Silberstein comment on it.

Karl_Northwind

cross post

so it's acceptable protocol here to cross post?

I will do so. It just seems that I could remove a large amount of water from the air with 50 deg water given the amount of condensation we get off the water pipes.





thanks

Karl

Mark Eatherton

Cross Posting is allowed....

Cross stiching, cross threading and cross dressing, are NOT allowed, Unless you are duly and properly licensed to do so... :-)



ME