heat transfer

[polkat]

I am on my fourth year with my OWB; i do have a few questions that i hope that you can answer 1. when the OWB is 180 the transfer heat threw the exchanger the furnace temp is 120/130 max i have a larger pump on the OWB is there any way to increase this temp. 2. my first year operating the OWB the pressure was around 5-6 psi this year its holding 8 psi not sure the reason my quess is that i am building gunk in my lines (3). i have read a thermostat for the circulator pump at the OWB that shuts it off the circ pump when the house does not call for heat would like more info; would that affect my domestic hot water exchanger. my pump runs 24-7 for about 8 months. i have hot water heat i(f that helps)

 

[rx7145]

What size lines do you have? Any underground heat loss? Also what size pump do you have?

 

[polkat]

the size of the lines are 1 inch lines there is signs of heat loss however; i have a temp gauge on the incomming line of the OWB just before it goes to the exchanger that temp is also 180. if the boiler temp at the boiler is 180 the temp inside is 180 before it goes into the exchanger. the pump is a grundfos up26-64f 1/12hp.

 

[Paso One]

What brand of OWB do you have?? 8 psi is what mine runs at 24 /7 Do you have radiant heat as well as the heat exchanger? 120 130 works good with radiant but not so good for heat exchangers. IMHO

 

[polkat]

I have a heatmor boiler, the boiler only runs the heat exchanger (it baisicly preheats my furnace water before it goes to the furnace i turn down the furnace water temp all the way down so it dosent call for heat the heat exchanger was somewhere in the middle of size for my home i have apx 3000 sqft house.

 

[oneoldbanjo]

Polkat:

The heat in your OWB is 180.....what is the 120/130 temperature you are measuring? Is it the temperature of the water into the heat exchanger, the water out of the exchanger, or the temperature of the air coming out out of the exchanger?

 

[oneoldbanjo]

Polkat:

I re-read your post and it appears the OWB is connected to a heat exchanger that runs 180 degree water in from your OWB and the water coming out of the exchanger goes to your indoor furnace boiler - and the water coming out is only 120-130 degrees.

To really understand what is going on - can you measure the temperature of the line going back to the OWB? Also do the same for the lines coming into and out of the exchanger for your indoor boiler. It would really help to know what kind of temperature changes are occuring on both sides of the exchanger (All 4 temperatures). If there is a huge change in the temperature difference on the OWB lines and very little on the boiler side - it would indicate the OWB side of the exchanger has little flow. If there is very little temperature difference between all 4 sides - it would indicate that the furnace side of the heat exchanger is getting little flow (or that the exhanger is undersized).

 

[polkat]

okay thank you i will have to get those strap on temp guages hope that they will be okay probally will get 4 of them and place them in and out of the exchanger on both sides I will let you know within a day or so thank you

 

[polkat]

checked over the weekend

its been warm here but i did have a chance to catch it running the strap on temp guages i purchased worked great it showed me that my temp ga on the furnace is junk here are the temps though boiler water in to plate exchanger 170 out of plate was 160, house side out of the plate is 140 . the times i did see that it was on there almost alway was a 20-30 degree difference between dont know if this is normal? it usually was messured half way of the thermostat cycle i didnot stick around for the full on off cycle.

 

[rx7145]

Sounds like the pump on the gas furnace is not running or is too small.

 

[polkat]

thats been my thought too but if i increase flow on the gas furnace side would the transfer heat decrease?

 

[oneoldbanjo]

If you increase the flow on the furnace side.....the temperature will probably get smaller.....don't buy a new pump yet. The more water you flow through on the furnace side....the less time it will spend in the exchanger and the temperature change will probably be less.

You are only getting a 10 degree drop in water temperature across the heat exchanger on the OWB side. What it the temperature increase on the furnace side? What is the temperature going in.......140 or less?

In a heat exchanger if we ignored the heat loss to the room, if you were flowing the same amount of water in the OWB side and the furnace side you should get the same amount of temperature change. If the OWB loses 10 degrees your Furnace water should gain 10 degrees. Now I am pretty sure you won't be flowing exactly the same amount of water in both loops - but knowing the temperature difference on the furnace side(in and out) would sure help to figure out what is going on. You have never mentioned that the temperature builds slowly and does get above 140.......it seems like the temperature will never get above 140?

 

[mtfallsmikey]

130 deg. supply air temp. is fairly normal, considering 180-185 deg. temp water. A gas/oil furnace will produce up to 190 deg. air at the discharge; maybe 150 deg. at the outlets...at least that has been my experience.

 

[oneoldbanjo]

130 deg. supply air temp. is fairly normal, considering 180-185 deg. temp water. A gas/oil furnace will produce up to 190 deg. air at the discharge; maybe 150 deg. at the outlets...at least that has been my experience.

I don't think that means much here.....he has hot water heat from what I can tell. The water out of the heat exchanger won't get above 140.

 

[polkat]

yes I do have hot water heat; for the readings that I was able to take all of them are with in this reading OWB into plate is 170 out of plate is 162 on the furnace side into the plate is 130 and out of the plate is 138. it has been warm here so there isnt a call for heat as much this reading has been taken when the house called for heat roughly half an hour running

 

[oneoldbanjo]

Maybe this is the problem.....how is your circuit plumbed? It sounds like the heat exchanger for your house is tied into your furnace loop and the pump only runs when you need heat. You should really have the heat from your OWB running into your inside furnace 24/7 - not just when you need heat.

Tell us about the plumbing or your system.

 

[polkat]

the OWB does flow into the heat exchanger 24-7 the house side of the exchanger (preheats the water before it goes into the furnace) I have one circulator pump dedicated only to the basement infloor heat the second is for the two zone valves on the other two floors this pump will only come on when there is a call for heat. i had another thought on the water flowing from the exchanger to the furnace I have a ball valve if I throttle that back I could slow the flow threw the exchanger but the valve is before the house circ pump (I didnt want to starve it and wreck the pump so I never attempted this yet)

 

[fletcher0780]

Has your system been like this since installed 3 years ago, or has the B side of you HE slowly been decreasing? It's possible your HE has lost efficiency due to sediment, or if has always been that way perhaps the HE is sized incorrectly.

What brand and size is your HE? do you have Y strainers on both in ports to trap sediment? Do you have temp gauges on all 4 ports of your HE?

On my system, I have 150ft (one way) of 1.25" TSP. My boiler temp is 170*, my HE side A input is 170* and side A output is 160-170* depending on what is calling. My side B input is usually around 145-165* and side B output is 165-170*. My OWB loop pump (side A) only runs when there is a call for heat, same with the side B loop through the oil boiler.

Not sure if this helps or not.

 

[oneoldbanjo]

I believe you need to have a pump and loop on the furnace side that will run 24/7 and transfer heat from your OWB to your Furnace all the time so that you can build the heat up insider your furnace water - regarless of the house calling for heat. At a minimum the pump in this loop should run until the heat in your furnace is up to the lower set point on your OWB.

The alternative would be to get a larger heat exchanger that can keep up with your demand....it sounds like the one you have does not have enough capacity to transfer more than 140 degrees from your OWB to the furance loop when the house calls for heat.

 

[polkat]

let me check what brand exchanger I have. the problem had always been there. I am going to have to check on the open loop on the house side this makes sence I am going to have to read more here so I am sure that you will be hearing a lot more of me thank you