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

[Streblerm]

This is why I love the Internet. A bunch of enablers confirming your ideas. Seriously though,

With a heat load that high, I don't think there will be many times that you won't need that 50 gallons of water you have already heated. Also not sure an on-demand heater would be designed to stand a continuous output that high - the load to heat a house is a LOT more than the load to heat DHW. Something to check out. It would either lead to the tankless heater running most all the time, or a lot of short cycling. I also don't think you will get much out of tying the heat pump water heater (desuperheater?) to this setup - coils need much hotter water than a desuperheater can produce, and you would lose some of the heat pump liquid heat to efficiency losses during the heat exchanger part of that. I think most people I know that heat their DHW with their geo system can heat their DHW with it, but only adequately.

I would likely do a condensing boiler with the biggest coil you can easily fit.

And replace the heat pump.

This is right along the lines of what I am thinking.

The Rudd setup I linked to the spec sheet uses one of their tankless water heaters along with an air handler with an A-coil and a water to air heat exchanger. It pretty much lists all their tankless heaters as possible heat sources. Before I buy one I will definitely check to see if they are rated for use with hydronic heating and if they can sustain the necessary output. There is quite a price range available, like 500-3000 dollars for tankless heaters. I'm sure plenty of them would not be suitable for heating.

As far as terminology goes it is my understanding that technically water heater vs boiler is the ability to heat water vs the ability To generate steam and condensing vs non condensing refers to effeciency. There are non condensing tankless water heaters that around 80% efficient and condensing tankless units that are around 95%. Condensing boiler is often used to refer to a any condensing unit but technically a boiler will make steam while a water heater won't. Most of the tankless units are capable of operating at a maximum of 150-199k btus and a minimum of 15-20k. My heating needs wouldn't necessarily max it out. I think they run a variable flame in order to do this. Some or all of this may be right, I'm still learning.

As far as the desuperheater goes you ar right there. It steals heat from the heat pump so in the winter time there would be no gain.

 

[NSMaple1]

On the water heater vs. boiler thing - 'boiler' is a term that is almost universal applied to an appliance that heats water for space heating (vs. domestic hot water). It doesn't mean it makes steam - it almost always does not, nowadays. A more accurate term would be 'hyronic heater', but that term is seldom used. Generally, 'water heater' is taken to mean heats water for DHW use, and 'boiler' means heats water for space (house) heating use - a 'boiler' usually doesn't actually boil the water or make steam (so is a bit of a misnomer). Except if something goes drastically wrong, or it is actually designed for a steam heating system, which is a rarity except maybe for industrial & institutional uses.

Condensing usually means the unit can output combustion gases at temperatures below what they would normally otherwise condense at (and non-condensing units must stay above) - thereby the added efficiency.

The primary advantage to on-demand units is that they only heat when the heat is actually needed, and that advantage can be utilized when the heat is not needed much and there are long periods in between demand. With space heating and much larger loads, that isn't so much a factor and becomes negligible. IMO.

 

[Streblerm]

While I appreciate all the information and discussion so far I am kind of surprised that nobody with an OWB is running one of these air coils.

 

[03HD2500]

I was mostly curious if any of the OWB guys are running a water to air hx, what size they are, and what kind of flow they are using.

When I did my install of my OWB I used a water to air hx and the size that I put in was a 16x22 and I think it is somewhere around 120k BTU. Not sure exactly sure what flow I am using but I was using a B&G NRF-22 circulator and ran it on high speed but now I replaced the 22 to a NRF-36.

 

[03HD2500]

I'm no HVAC expert, but I think you'll find most OWB's are set up with the largest heat exchanger that will fit in the plenum

That is correct! That's how I sized mine.

 

[Streblerm]

When I did my install of my OWB I used a water to air hx and the size that I put in was a 16x22 and I think it is somewhere around 120k BTU. Not sure exactly sure what flow I am using but I was using a B&G NRF-22 circulator and ran it on high speed but now I replaced the 22 to a NRF-36.

It looks like that is around 36 gpm max.

What kind of temps are you running for the loop?

I guess the big question is are you happy with the performance, i.e. Does it provide enough heat?

 

[03HD2500]

Around 170-180

 

[mtfallsmikey]

I used Heil hydro-coils, one on my oil furnace in my house, shop/garage has a stripped down gas furnace with blower in it, fan relay, hydro-coil. Heat loss calc for house was 46K BTU, coil I use is rated for 56K BTU @ 180 deg. water temp. At that water temp, I realistically get 120 deg. air out of the diffusers. during the coldest days, I wind up the temp on the OWB to 190.

 

[mtfallsmikey]

I'm no HVAC expert, but I think you'll find most OWB's are set up with the largest heat exchanger that will fit in the plenum. I don't know about the efficiency numbers as that seems kind of high for the whole system.

That's the way most OWB dealers size piping/coils, or on your home's square footage, which is BS... do a heat loss calc. and do it right!

 

[H-Ranch]

That's the way most OWB dealers size piping/coils, or on your home's square footage, which is BS... do a heat loss calc. and do it right!

To design a new system on a clean sheet of paper that is definitely the best way. Sometimes the practicality to adapt to existing my dictate less than optimum sizing. If the original system is sized properly it may be close anyway. *shrug*

 

[Streblerm]

My plans long term are to switch the house, at least partially, to radiant. I'm not sure how yet. Pex, baseboards, radiators or maybe a combination. I am working on the room by room heat loss calculations to see how they match up with the whole house. I also just ordered Modern Hydronic Heating by John Siegenthaler. It appears to be a well respected textbook on radiant design. I've been reading about radiant in ceilings and walls. Radiant cooling with my geo ground loop may even be possible. Pretty interesting stuff.

I have gotten burned by so called experts on my existing heating system. I'm not going to do it again. I will build this system right. I know it won't be cheap, quick or easy. The calculations and plumbing are within my ability. I am going to build it over time but it will be designed from the beginning. First I want to experiment just a bit to get my feet wet.

Interesting about the water to air HX. The performance curve is only shown at fairly high temperatures. I didn't intend to run my system at that high of a temp. This is where a bigger air coil might help. I think I can get a 20x22 in my plenum.

 

[mtfallsmikey]

My plans long term are to switch the house, at least partially, to radiant. I'm not sure how yet. Pex, baseboards, radiators or maybe a combination. I am working on the room by room heat loss calculations to see how they match up with the whole house. I also just ordered Modern Hydronic Heating by John Siegenthaler. It appears to be a well respected textbook on radiant design. I've been reading about radiant in ceilings and walls. Radiant cooling with my geo ground loop may even be possible. Pretty interesting stuff.

I have gotten burned by so called experts on my existing heating system. I'm not going to do it again. I will build this system right. I know it won't be cheap, quick or easy. The calculations and plumbing are within my ability. I am going to build it over time but it will be designed from the beginning. First I want to experiment just a bit to get my feet wet.

Interesting about the water to air HX. The performance curve is only shown at fairly high temperatures. I didn't intend to run my system at that high of a temp. This is where a bigger air coil might help. I think I can get a 20x22 in my plenum.

John Sigenthaler is the radiant guru. also suggest you look at Dan Holohan's books as well.

 

[hupte]

I think it's a Dragon Breath heater.

http://www.dragonbreathheaters.com/products/unit-heaters/

those heaters are really expensive here is the same thing for almost half the price.
http://stores.ebay.com/freeheat4u2/...=12069463&_sid=20017572&_trksid=p4634.c0.m322

 

[Guswhit]

I built one for a lot less than that in my last garage from a fan salvaged from a furnace. Just made some pieces of metal to neck it up from the blower side of the fan to the exchanger side and pop riveted it together. Ill look for a picture.

Sent from my SCH-R970 using Tapatalk

 

[hupte]

My plans long term are to switch the house, at least partially, to radiant. I'm not sure how yet. Pex, baseboards, radiators or maybe a combination. I am working on the room by room heat loss calculations to see how they match up with the whole house. I also just ordered Modern Hydronic Heating by John Siegenthaler. It appears to be a well respected textbook on radiant design. I've been reading about radiant in ceilings and walls. Radiant cooling with my geo ground loop may even be possible. Pretty interesting stuff.

I have gotten burned by so called experts on my existing heating system. I'm not going to do it again. I will build this system right. I know it won't be cheap, quick or easy. The calculations and plumbing are within my ability. I am going to build it over time but it will be designed from the beginning. First I want to experiment just a bit to get my feet wet.

Interesting about the water to air HX. The performance curve is only shown at fairly high temperatures. I didn't intend to run my system at that high of a temp. This is where a bigger air coil might help. I think I can get a 20x22 in my plenum.

I'm running an owb, with a water to air hx in my furnace. I have also installed several other water to air hx for owb's in other ppl's house. my water comes in at 171-181* the return lines temp varies from 150-179* depending on my heating needs. when the blower for the furnace is running the water temp drops 20-25* I'm running a manifold setup and flowing 2 gallons per minute into my furnace.

I installed the biggest water to air HX I could fit because at the time I had an old drafty farm house with single pane windows. and my 100k btu furnace would run 24hrs a day and the house would be 65 on the windy days and nights. (I remodeled the house since then) I like to size the unit as big as the furnace will fit cause I like saving money. the bigger the water to air HX the less your furnace blower will run. also the bigger the hx in your plenum. the more heat it will radiate when your furnace blower isn't running... Yes, you can size it to the exact right size, but I know many ppl who's houses wouldn't stay warm enough during the polar vortex's. my house was warm cause I over sized my heating unit. to me giving yourself a lil extra heat is like giving yourself a lil extra money in the bank. ya you might not need it this month, or even this year. but when you do need it, it sure is nice to have it. the cost of a bigger water to air HX is minimal compared to what you save on your electric bill. so to me the smartest and most economical thing to do is to get the biggest water to air hx possible.

 

[avason]

While I appreciate all the information and discussion so far I am kind of surprised that nobody with an OWB is running one of these air coils.

I run an OWB that runs through my furnace then to separate air handlers. Basically the water runs through the coils and a squirrel cage blows the hot air. I heat about 3800 square feet. This set up works pretty well. I will be putting radiant heat in my great room because I feel the heat goes up to the high ceiling.

 

[Streblerm]

I don't think oversizing the heat exchanger is ever a bad idea. Unless it is so big that it affects flow in some way. That is kind of the principle of the condensing furnace/boiler. Squeeze all the heat that you can out of those exhaust gasses before you vent them.

Oversizing the heat source is a different story. What I am reading about the condensing boilers is that you really don't want to short cycle them. The beauty of the high efficiency boilers is that they are variable flame so I can just change the water temp going through the loop as temperature conditions dictate. There are probably fancy thermostats that would even do it for you.

 

[Streblerm]

I'm running an owb, with a water to air hx in my furnace. I have also installed several other water to air hx for owb's in other ppl's house. my water comes in at 171-181* the return lines temp varies from 150-179* depending on my heating needs. when the blower for the furnace is running the water temp drops 20-25* I'm running a manifold setup and flowing 2 gallons per minute into my furnace.

I installed the biggest water to air HX I could fit because at the time I had an old drafty farm house with single pane windows. and my 100k btu furnace would run 24hrs a day and the house would be 65 on the windy days and nights. (I remodeled the house since then) I like to size the unit as big as the furnace will fit cause I like saving money. the bigger the water to air HX the less your furnace blower will run. also the bigger the hx in your plenum. the more heat it will radiate when your furnace blower isn't running... Yes, you can size it to the exact right size, but I know many ppl who's houses wouldn't stay warm enough during the polar vortex's. my house was warm cause I over sized my heating unit. to me giving yourself a lil extra heat is like giving yourself a lil extra money in the bank. ya you might not need it this month, or even this year. but when you do need it, it sure is nice to have it. the cost of a bigger water to air HX is minimal compared to what you save on your electric bill. so to me the smartest and most economical thing to do is to get the biggest water to air hx possible.

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

 

[NSMaple1]

2 gpm at a 20° temp drop is around 20,000 btu/hr. Or almost 30,000 btu/hr for a 30° drop.

That's not an overly large heat output - might work for some, not for others.

You also want to try to keep your boiler return temp above 140 or so, to avoid excessive creosote condensation in the firebox. If you're drawing the water down more than that (say with infloor or radiant), you'd want a bypass setup on the boiler to warm the returning water before it hits the boiler.

 

[hupte]

2 gpm at a 20° temp drop is around 20,000 btu/hr. Or almost 30,000 btu/hr for a 30° drop..

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=A0LE...s-EN.pdf/RK=0/RS=s8_oRfCnplwb0y_6C77nuzp1qkk-