Ask Me Help Desk - Converting an R22 A-Coil To a Water to Air Coil?

Converting an R22 A-Coil To a Water to Air Coil

A friend of mine has a water to water geothermal unit for heating his home. He wants to use this same unit for cooling the house. Looking at water to air coils the prices are quite steep compared to the standard run of the mill A-Coils. We are thinking of converting a refrigerant to air A-Coil to a water to air A-Coil. The plan is to unsolder the high side small tube connections and replace with 3/8 connections to a common manifold. Chilled water will be circulated through the A-Coil for cooling. Has anyone else attempted this type of conversion? Any comments on why this wouldn't work?

Thanks,

Eric D

It might work BUT you cannot extract much heat out with an A coil design.
3/8 inch tubes will not give much of a flow rate. So the answer is no.

Take a good look at a real hot/chilled water coil. Usually a minimum of 3/4 inch copper and many passes depending upon the BTU capability.

Basically hot and chilled water coils are made the same except for the condensate pan and drain on the chilled water coils.

You could do a switch over valve set up like a commercial unit but the coil you have for heat now probably does not have the pan for the condensate to drip on as the water is pulled out of the air in chilled mode.

BTW my chilled/hot water coil has 1 and 1/4 inch copper feeder for a great flow rate.

Quote:

Originally Posted by hvac1000

BTW my chilled/hot water coil has 1 and 1/4 inch copper feeder for a great flow rate.

Hvac,

What is the tonnage or BTU rating of your coil? What is the delta T across the coil for the water and air?

Here are my thoughts why I’m going to help my friend try this. We have 3.5 ton A – Coil that normally would be scrapped. So to modify it the only thing we can loose is our time and a few pieces of tubing. This coil has a ¾ inch outlet that 6 each 3/8 inch tubes dump into. What use to be the high pressure side of this coil, also has 6 each 3/8 inch tube connections. The total tubing area for the inlet of these 6 ea 3/8 tubes is .456² inches. The area of the ¾ inch outlet is .348² inches. Understanding that there are some flow restrictions, I should still be able to flow 6 to 7 gallons per minute. I think a conservative delta T should be round 10 to 15° F. At this rate it should produce about 3 to 3.5 tonnage.

I would be interested in your thoughts. If there is an interest I’ll update our progress on this experiment. As of last night I have removed the 6 high pressure 3/16 tubes from the inlet sides of the A coil 3/8 tubes.

Eric D

The coil BTU will depend upon the temp of the water entering. If you run 140 degree water your BTU will be less than 190 degree water.

Now with that said there are three hot water coils in this house and I will use the largest as a example.

At 180 degree water the factory calculation is 150,000 BTU out with standard flow from the pump.

Normally a high delta T is not recommended but in my case I designed a system that works well with a high Delta. Water in coil at 180 water out of coil 140. Now that is a insane number but I use a variable flow pump and valve system. Delta T 40

I have no problems with condensation all the way down to 120 degrees since the boiler is a instantaneous built in 1980 and it is all copper/brass/stainless steel in its make up. When using a instantaneous that cool water is heated pronto unlike a cast iron or steel storage type unit.

With outside sensors and with the aid of a computer program the system will cycle down to 25,000 BTU's and still preform very well. I use a CAC system for air modulation control over the coil and that matches the coil temp with the use of a computer style program for control of the entire system.

To recreate this system would be far to costly and time consuming. When I pass from this world I told my wife that someone is probably going to want to rip out all my stuff and replace with a standard boiler system. This is because no service person in this area will ever figure it out and out of fear and time for learning they will take the easy way out and replace the system.LOL

I played around with many fun ideas when I was a very young man but as I got older I kind of gave up that ghost.

Good luck with your project and have some fun with it.

Quote:

Originally Posted by hvac1000

To recreate this system would be far to costly and time consuming. When I pass from this world I told my wife that someone is probably going to want to rip out all my stuff and replace with a standard boiler system. This is because no service person in this area will ever figure it out and out of fear and time for learning they will take the easy way out and replace the system.LOL

Hvac,

First off let’s hope you will be around for a long time to come. Your heating system sounds like one interesting setup. One thing you might consider is writing a BLOG with photos of your system. I find as I get older the BLOG works like a diary of my more then simple projects. I also include a lot of photos. Later on down the road I can refer to the BLOG to remember how I did something and also to share with friends that have the same interest.

On your system do you use the same coil for cooling? If yes, what do you use for chilling the water?

Quote:

Originally Posted by hvac1000

I played around with many fun ideas when I was a very young man but as I got older I kind of gave up that ghost.

Good luck with your project and have some fun with it.

I find I play around with more stuff now that I'm older. Always trying to learn something new. Thanks for the luck, and yes, I'm sure I'll have fun. BTW, I've had a few major desasters in the past... but they still were fun and I still learned something, even if it was that I shouldn't do something EVER again.:cool:

Regards,

Eric D

I used to have a very small natural gas chiller that were popular back in the 50s and 60s. The ammonia system went south so I switched to a separate coil.

Hi, how did you make out with the coil. I have similar situation with a recently installed GeoThermal. I gues I have till summer to figure it out.

Quote:

Originally Posted by acaetano22

Hi, how did you make out with the coil. I have similar situation with a recently installed GeoThermal. I gues I have till summer to figure it out.

Hey there! Wow, I almost forgot about this thread until I got an email telling me that someone had posted to it, that being you. Thanks!

The conversion went very well. I found that silver solder works best for all the connections. The test of this conversion unit came out close to 15° F delta T bogey we were shooting for. It is nice to take something that most folks would write-off as gunk and make it into something useful. Total conversion took me about 3 evenings of work. Now that I know what I'm in for, I could do the conversion in about 1 to 2 evenings at most.

Regards,

Eric D

Hi everyone:

I'm looking to do almost the same project as Eric. I'm trying to make an evaporative cooler heat exchanger that uses water to cool air. I plan to use evaporative cooling to cool a pan of water to about 70 degrees (F) then circulate the chilled water through a cooling coil recovered from an old air conditioner. Here's my question: The water that I'm using as a coolant will be about 17 degrees (F) colder than the outside air. I'm hoping to cool the air by 10 degrees. Will this work? I'm going to be using a blower that's about 3000 cfm. What size coil will I need to cool that amount of air by 10 degrees? How much 70 degree water needs to be pumped into the coil to maintain the temperature of the coil? Is there a formula? Please send links.

Thanks,
Other Eric