Looking for info on water to air heat exchangers/hydronic forced air

[hupte]

So 2 gpm is getting the job done? That is good to know.

I just put in the manifold system this year. I would prefer more flow thru the water to air HX. but it does ok so far. but its not really cold yet.

 

[NSMaple1]

something isn't adding up. my heat output with my boiler is much higher than my 100,000 btu high efficiency gas furnace. so either my high efficiency furnace is 10 percent efficient. or I'm getting more than 2 gallons per minute, thru my 2 gallon per minute manifold. or your numbers are off. maybe you meant btu's per minute not hour?

(here is a link to my manifold) http://r.search.yahoo.com/_ylt=A0LEVrdVU05WqrgAfesnnIlQ;_ylu=X3oDMTByOHZyb21tBGNvbG8DYmYxBHBvcwMxBHZ0aWQDBHNlYwNzcg--/RV=2/RE=1448002517/RO=10/RU=http://media.wattswater.com/download/WR_WattsRadiant_Catalog_FullLine_04_Manifolds-EN.pdf/RK=0/RS=s8_oRfCnplwb0y_6C77nuzp1qkk-

1 btu = 1 lb. of water 1 °F.

1 gallon of water = 8 lbs.

2 gpm = 120 gph.

So, 20° x 8 lbs x 120 gph = 19200 btu/hr.

That's what I come up with.

 

[hupte]

1 btu = 1 lb. of water 1 °F.

1 gallon of water = 8 lbs.

2 gpm = 120 gph.

So, 20° x 8 lbs x 120 gph = 19200 btu/hr.

That's what I come up with.

ah-ha!!!! I got it I came up with the reason why the numbers aren't adding up. I'm measuring my incoming water and my outgoing water. I have a manifold set up that sends water to 4 different sources. only one of those sources is the forced air furnace. so the cold air from the furnace is being mixed with the (relatively) hot water of the plate HX, (which doesn't cool the boiler water unless the faucet is running) the base board heaters, (which often don't call for heat) and the clothes dryer (which also often doesn't call for heat). so thats why we aren't getting an accurate reading. really what I need to do is put a temp gauge on the return for the cold water on the water to air HX for an accurate formula.

 

[Oxford]

Good morning,

I do this for a living. A couple things for you to be aware of:

First, regarding a heat source. I recommend the use of a condensing boiler, but be aware that when using an air-to-water HX the discharge temperature of the air is going to approach the temperature of the boiler water. If your boiler has satisfied during an off cycle of the air handler, when it cycles back on it's going to take a period of time for the discharge air temperature to warm up and stabilize. Large commercial systems don't have this problem, since they typically have multiple loads and high system volume. The solution for a small system is a storage tank, and it's almost always going to be bigger than you think it should be. If you put in a condensing boiler, be very, very, very attentive to water chemistry. Because the heat exchangers are constructed with relatively small passages to allow extraction of the last little bit of heat, and they are very prone to fouling if you have water quality issues.

Second, regarding your system. As I read it, your main problem is on the geothermal heating side, both with expense and comfort. The best way to use a boiler with a geothermal system is to put it in the field loop and run it during heating season to maintain loop temperatures at a point that allows full output from the Geo system, which keeps the system from using its resistance heat. The next best way is to use a HX in the air stream to raise supply air temperature for occupant comfort. In your case, this could be accomplished by piping your boiler so that it supplies a storage tank at a constant temperature, which then feeds a pair of heat exchangers, one water-to-water on the ground loop and one water to air in the discharge air stream, both heat exchangers fed by dedicated pumps and both flow-controlled via thermostatically controlled three way valves. You could then disconnect your resistance heat, your geothermal system could run efficiently, and the air would be warm coming out of the ducts.

Third, regarding radiant cooling. I like Siegenthaler, but radiant cooling using groundwater in the Midwest is a pig in a poke, because our dewpoint are too high for about 360 days a year. If you don't have water cold enough to get air below the dew point necessary for comfort cooling, which is 55 degrees F, all you're going to be is clammy, and without a chiller you're not getting that. Spend your money on fixing your geothermal cooling and be done with it. Geothermal systems should not be difficult to diagnose and repair. If your current guy is struggling, you need a different guy.

Fourth, regarding system design. Whatever you do, as you install this system, put thermometers and pressure gauges on each side of every load and every source, and put flow control valves on the outlet of every load. Nearly every hydronic problem I have seen discussed on this forum in five years could have been diagnosed in five minutes with accurate temperature and pressure information, and most of them could have been resolved in about that much longer with flow control valves. Instead, people jack around for weeks in cold houses, going at it by guess and by gosh and getting nowhere, because they don't take the time to know the theory and use their brains.

Good luck, whatever you do.

 

[Streblerm]

Second, regarding your system. As I read it, your main problem is on the geothermal heating side, both with expense and comfort. The best way to use a boiler with a geothermal system is to put it in the field loop and run it during heating season to maintain loop temperatures at a point that allows full output from the Geo system, which keeps the system from using its resistance heat. The next best way is to use a HX in the air stream to raise supply air temperature for occupant comfort. In your case, this could be accomplished by piping your boiler so that it supplies a storage tank at a constant temperature, which then feeds a pair of heat exchangers, one water-to-water on the ground loop and one water to air in the discharge air stream, both heat exchangers fed by dedicated pumps and both flow-controlled via thermostatically controlled three way valves. You could then disconnect your resistance heat, your geothermal system could run efficiently, and the air would be warm coming out of the ducts.

Right on the money. It's not that my current system is incapable of keeping the house comfortable, rather It is not economical for me to keep the house comfortable. I also get diminishing returns. As the heating season progresses, the ground loop temp drops which lowers the amount of heat available. I have been thinking about heating the ground loop but I didn't know if it was something that was done. Thanks for that info. What stopped me from considering it as an option was that I assumed that heating water to heat water to heat refrigerant to heat air probably wouldn't be economical. Really if I could just replace the resistance heat with something more economical then I could probably live with the economy and comfort of the system.

Third, regarding radiant cooling. I like Siegenthaler, but radiant cooling using groundwater in the Midwest is a pig in a poke, because our dewpoint are too high for about 360 days a year. If you don't have water cold enough to get air below the dew point necessary for comfort cooling, which is 55 degrees F, all you're going to be is clammy, and without a chiller you're not getting that. Spend your money on fixing your geothermal cooling and be done with it. Geothermal systems should not be difficult to diagnose and repair. If your current guy is struggling, you need a different guy.

Radiant cooling isn't a main consideration in the design of my heating system, rather a curiosity. The geo excels at cooling. A commonly refer to it as my 16k air conditioner. My focus is on economical heating.

As far as repairing my current system it is again a question of economy. I have actually had four techs out to look at it and only one has even proposed a diagnosis and solution at a cost of $1200. I doubt his diagnosis and there is no guarantee. $1200 is probably half of the cost of buying a new, more efficient, properly sized geo unit when you factor in the tax rebate.

For that matter at 0 for 4 so far on techs that might be capable of repairing my current unit I am rapidly approaching replacement cost just in service calls.

Good luck, whatever you do.

Thank you.

Regarding heating the geothermal loop. Could I run the same brine in the hydronic loop and directly circulate the geo loop through the boiler or should I isolate the geo loop with an HX?

If isolation of the geo loop is the way to go then would it be beneficial to use distilled water in the hydronic loop?

 

[Oxford]

Your system has two sides, the refrigerant side and the water side. In cooling mode you reject heat to the water side, which then transfers it to the earth through water flow. In heating mode you gain heat by reversing the refrigerant cycle, using the heat of the water, gained from the earth, to boil refrigerant, then using your house as the condenser. When you read the books, whether it's Siegenthaler or Holohan, they are going to discuss primary/secondary pumping. Right now, you have one water loop to the field. When this is done, you're going to have two primary loops- one to the field, one to the boiler via a heat exchanger, and a secondary loop to which both primary loops are coupled. Flow through the loops will be controlled by pumps via thermostatic control based on loop temperature and outdoor temperature, with the goal being proper loop temperature according to system mode. The secondary benefit of loop flow control will be to avoid rejecting any boiler heat into the earth during heating season, i.e. the field will be isolated when it no longer contributes to the heating system.

Regarding your current system, there are only about six moving parts in a refrigeration system. The principles are consistent and not terribly complicated. What is your system doing or not doing that is such a novel problem that four people cannot figure it out?

 

[Streblerm]

Good morning,

I do this for a living. A couple things for you to be aware of:

First, regarding a heat source. I recommend the use of a condensing boiler, but be aware that when using an air-to-water HX the discharge temperature of the air is going to approach the temperature of the boiler water. If your boiler has satisfied during an off cycle of the air handler, when it cycles back on it's going to take a period of time for the discharge air temperature to warm up and stabilize. Large commercial systems don't have this problem, since they typically have multiple loads and high system volume. The solution for a small system is a storage tank, and it's almost always going to be bigger than you think it should be. If you put in a condensing boiler, be very, very, very attentive to water chemistry. Because the heat exchangers are constructed with relatively small passages to allow extraction of the last little bit of heat, and they are very prone to fouling if you have water quality issues

If I understand what you are saying here: the air to water HX is capable of removing almost as much heat from a volume of water as the boiler is capable of supplying. So if the boiler is off it will take a little while for the air and water temp to come up. The amount of time in minutes that it will take would be the ability of the boiler to heat divided by difference between maximum temperature rise of the boiler for a volume of water and the temperature delta of that water through the HX ? If my boiler can heat 10gpm 30 degrees and I am running 10 gal per minute through an HX with a TD of 27 degrees then it would take about ten minutes to reach desired temps. Other than affecting comfort is this an efficiency issue?

Could I simply address this by raising the temperature of the condensing boiler as it got colder outside? That way it would minimize startups. I am thinking about keeping dhw and heating totally separate at this point. Is there really much difference between keeping a tank of water hot for your heating vs having a separate Dhw heater (which I already have). Would sizing the HX closer to the designed max btus rather than oversizing it minimize this as well?

I am ok with not always getting HOT air out of the ductwork. The comfort problems were more that it was costing me 4-500$ per month to only keep the house 65f. Unless the heat strips were going the air coming out of the ductwork was only 15-20 degrees warmer than ambient temp due to leaking ductwork which is another issue. If I could just rep,ace the resistance heat with something more economical that would be fine. With the cost of gas I'm thinking I may design the hydronic at around 80% of my heating load and use the geo as backup.

I know this is a lot of questions and I appreciate everyone's input. Some of these questions I am just asking myself. It is helpful to me sometimes just to get them out of my head and into text. None of these questions are designed to be argumentative. I am just trying to understand. Conversation and debate really help me to do that.

 

[Streblerm]

Regarding your current system, there are only about six moving parts in a refrigeration system. The principles are consistent and not terribly complicated. What is your system doing or not doing that is such a novel problem that four people cannot figure it out?

I know, right. I am certified and trained to work on automotive a/c and I do understand the refrigeration cycle. The short story is that I suspect either a faulty TXV and/or a relatively small leak. It is a climate master/carrier of an age where there were TXV issues. And it is an r-22 unit which makes anything to do with charging it expensive.

Last year it was kicking out on the water coil low limit in heat mode I called a local heating company with a good reputation. He arrived with no means of checking the water loop and diagnosed low charge.he didn't strike me as terribly knowledgable and He suggested I contact the original installer who I had pretty much written off based on what I consider to be a poorly designed and executed system.

I went back to the original installer and told him it wasn't working and that I suspected either low charge or bad TXV. Their service tech came out with no means of evaluating the water loop. He diagnosed it as low charge, guesstimated on the amount and shot a couple pounds of r-22 and a can of stop leak. He then explained that leaks were hard to find but his miracle goo should do the trick. About a week later I got a bill for $600 for a service call, two hours of diagnosis, and 2.5 pounds of freon. I called the owner to ask him what the long term plan was for fixing the unit and how the warranty would work as I didn't consider a can of stop leak a fix. he stopped taking my calls. It was working in heat mode. This was last February.

Flash forward to the end of April. Geo is still working in heat mode but when we switch over to a/c it is kicking out on a high pressure fault. I called a one man band who was recommended by a friend. He has no means of diagnosing the ground loop, at least listens to my story. He throws the gauges on and says yep, it looks like it's overcharged. You're not supposed to do this but I am going to bleed off some of the refrigerant. That didn't work and now the unit works neither in heat nor cool. He then tells me he probably let too much out and he will cut me a deal on putting some r22 back in. I told him to GTFO and bought a couple window units.

Well that brings us to the beginning of this heating season so I decided it's time to try another tech. The wife is none too excited with the prospect of 100% wood stove heat. He does diagnose the ground loop as working and that it has a low charge. He believes he found a small leak that is coincidentally in an easy to access location. The charge to fix the leak will be in the neighborhood of $1200 with no guarantee that his diagnosis is correct. And I suspect that it isn't. At this price with no guarantee it will work I decide it isn't worth it to put any more time or money into the unit. I'm already at close to $900 in service calls and diagnosis charges with a still non functional unit.

There was actually a fifth technician who came well recommended. He was interested in selling me a 140k btu gas furnace and 5ton a/c and not so much interested in looking at the geo. when I told him that the geo with strip heat at less than 75k btu was sufficient to heat my house, just not economically he insisted that he was correct and that the smallest furnace he would install was 125k btu and that he would not guarantee that it would keep me warm. Needless to say I thanked him for his time and sent him on his way. At least he didn't charge a service call.

Not to mention there were two other places I got recommendations for who did not service geos

Maybe I'm just too picky. I want my expensive heating system to turn on, be comfortable, and be economical. Six of the six people including the original installer have failed to meet my desired outcome. I don't really want to do the install myself but I think I might have to. At the very least I will take the time to design what I want and then pay an installer to do it. I'm beginning to believe that there are no technicians out there, only installers.

 

[Oxford]

Well, here's what I would do if I were on site:

1. Throw an amp clamp on the water pump to make sure that it's moving water. Hopefully somebody put pressure gauges on the inlet and outlet, so with differential pressure and amperages you can Take a look at the pump curve and it should tell you what the flow is, if it's flowing.

2. Gauge up to the system and see if it has any refrigerant left at all. If it does, reclaim it so that I could put it back in when I'm done fixing the leak. Hopefully water doesn't squirt out of the Schrader valve. If it does, the refrigerant to water HX is bollocks and now you're in a trick bag.

3. Pressurize the refrigerant side with dry nitrogen and a tracer of 22 so my leak detector will work. Use a refrigerant detector/ultrasonic detector/soap bubbles to find the leak.

4. Fix the leak

5. Re pressurize to 300psi with nitrogen and leave it overnight.

6. Dump the nitrogen, change the filters, evacuate to 500 microns.

7. Weigh the factory charge back in. 22 is expensive, but it's not crazy. Don't be scared.

8. Start the system and check pressures, set superheat as needed.

It's not complicated. "Don't work on geothermal systems." Who says that?

 

[NSMaple1]

I'm having a hard time understanding how pumping boiler heat into a ground loop can be a good thing. At that point why not shut the geo down & put the boiler heat right into the house? It would seem that if that was needed, there is a design issue or equipment malfuntion or shortcoming with the geo system that would make further operation of the geo in that current state a losing proposition. Even more so if it involves taking boiler heat and exposing it to the ground.

 

[Streblerm]

Well, here's what I would do if I were on site:

1. Throw an amp clamp on the water pump to make sure that it's moving water. Hopefully somebody put pressure gauges on the inlet and outlet, so with differential pressure and amperages you can Take a look at the pump curve and it should tell you what the flow is, if it's flowing.

2. Gauge up to the system and see if it has any refrigerant left at all. If it does, reclaim it so that I could put it back in when I'm done fixing the leak. Hopefully water doesn't squirt out of the Schrader valve. If it does, the refrigerant to water HX is bollocks and now you're in a trick bag.

3. Pressurize the refrigerant side with dry nitrogen and a tracer of 22 so my leak detector will work. Use a refrigerant detector/ultrasonic detector/soap bubbles to find the leak.

4. Fix the leak

5. Re pressurize to 300psi with nitrogen and leave it overnight.

6. Dump the nitrogen, change the filters, evacuate to 500 microns.

7. Weigh the factory charge back in. 22 is expensive, but it's not crazy. Don't be scared.

8. Start the system and check pressures, set superheat as needed.

It's not complicated. "Don't work on geothermal systems." Who says that?

Ballpark what would that cost? Want to make a trip to NE Ohio? All anyone around here wants to do is sell me a new one. I've been through the web, BBB, Internet searches, Angie's list. Even the people who install lots them don't seem to have a good track record for fixing them. I'm sure I could keep trying random people and maybe find someone to fix it but it costs me $100 every time someone comes out. I'm getting tired of paying to explain to some jag off how a geo works.

 

[fordf150]

Ballpark what would that cost? Want to make a trip to NE Ohio? All anyone around here wants to do is sell me a new one. I've been through the web, BBB, Internet searches, Angie's list. Even the people who install lots them don't seem to have a good track record for fixing them. I'm sure I could keep trying random people and maybe find someone to fix it but it costs me $100 every time someone comes out. I'm getting tired of paying to explain to some jag off how a geo works.

It doesn't get any better when it's just a simple propane furnace with heat pump. A total of 4 different guys and I gave up. Bought a set of gauges, dye, jug of 410 and went to town on my system. 5 minutes in I found the elusive leak... Another hour and the system was charged and cooling this spring. Worked like a dream all summer but now the heat pump doesn't function..... Switched to propane and moved on. I don't have time to diagnose it and have spent about the same money as you on incompetent techs that never could fix my heat pump.... Hasn't worked since the first day it was installed

 

[Oxford]

Hi nsmaple1,

I know these have gotten long, and I apologize. I agree, I wouldn't want to put boiler heat into the ground either, which is why in post 46 above I suggested putting the boiler and the ground field on separate primary loops, so that you can isolate either of them when not needed.

 

[Streblerm]

I thought I'd give an update for anyone who is interested.

I completed a detailed room by room heat loss analysis for the house which was eye opening. I came up with a total of 50k btu output, delivered to each room appropriately as being enough. It really highlighted the limitations of my ductwork and confirmed what I suspected. 75k btu output is what I would need in a forced air furnace and that I am loosing a significant amount (1/3) of my heat in the ductwork. It also pointed out that the rooms that are cold have inadequate air supply and return.

I bought an 18x18 water to air heat exchanger for $115. I am over simplifying as there are many variables for output based on water flow/temp/airflow but it is capable of delivering 40k btus @ 120 water temp and 100k btus @ 180. It is installed in the plenum and hooked up through the water desuperheater circuit of the geothermal to my existing water heater. It was my intention to make use of the pump since it was already there. It turns out the pump is toast. Not only the cartridge but the windings are shorted. There goes that idea. I guess I should have checked it's function before I plumbed it in. Oh well, live and learn. I already ordered another one. It is comical that the one part of the geo I intended to salvage is NFG.




Long term plans are to upgrade ductwork and balance. Replace geothermal unit with one more appropriately sized for my cooling load. Continue designing a closed loop hydronic air coil system for backup heat. The rooms that are cold are obviously under fed through the existing ductwork. I think I can correct this rather than adding radiant heat. There is only one room that I'm not sure I can fix with ductwork. It is a 2 story foyer/stairwell with two exterior walls and floor and ceiling exposed. It alone will need about 8000btus. It is currently served by only one 2x12 register.

I know the current system is open and I understand the concerns with such a system. In my defense it is only a test mule, call it version 1.0. It is also not significantly different than the desuperheater circuit that the original installer (incorrectly) built so I can't see that it is really any more dangerous to my family's health than what I already had.

 

[Streblerm]

I thought I’d dig this post up for a little update. I ran the combo of water to air heat exchanger/ gas hot water heater with resistance backup heat for the past three years and it worked pretty well. Of course I was also burning wood in the stove too. The only time it was an issue was after three showers in a row with the heat running you were stuck with Luke warm water.

Over that time I did a lot of reading, scheming, and figuring and here’s what I came up with:

I have natural gas. It is cheap now and for the foreseeable future so that should be my main fuel for heat

We have about a 7 month heating season and a 4 month cooling season so the focus of my HVAC should be on the H, not so much on the C.

There are all kinds of really neat heating options but there is a reason one type (spoiler-forced air combustion) is more common than others. That doesn’t mean that other options aren’t good but it does mean one is more proven.

So in the end I decided to put in a two stage 100k btu gas furnace with a 3 ton a/c unit and so far I couldn’t be happier. There’s just no payback on the geothermal. Heck, unless electricity gets significantly more expensive there isn’t even a payback to put in a really high efficiency a/c or heat pump. I eliminated the zoning system and balanced the duct work better and I now have the house within 2 degrees from the warmest to coldest room. I’m still working on more cold air return. We’ll see how much it costs as this is the first month. By my calculations it should cost about half as much to run as my cobbled heating system and be capable of providing 30% more heat.

I don’t intend to stop burning wood either. The stove is in the center of the house in its largest room. It seems to be playing well with the new furnace.