Boiler delta t?

[muleman51]

I'm having trouble getting my storage up to temp. Probably too small of boiler but that said, how much delta can I expect. I have a thermovar valve that keeps the incoming return to boiler at 140-145 external pipe temp. It seems that the boiler puts out a pretty much constant temp of 165-170 ( this is internal water temp at top of boiler and just before going into storage). The pump is on constant circulation and is 1" black pipe. The storage temp coming to the house has been 130- 170 depending if I'm home all day to keep it fired all the time. My storage room is between 80-110 most of the time. I may just move out there for the winter. I"m going to try and add more insulation to the tank today to try and lower the temp, although it does dry wood well. My pipe insulation is back ordered. But I was concerned that I don't get that much heat off the boiler and started to think that maybe that's all the delta I can get. Stack temp ranges between 225-300 internal. If I don't have all the numbers you need, I'll try to get them. Thanks Jim Hope everyone has warm, safe and happy new year.

 

[WoodNotOil]

Try turning the boiler up to 180 or even 185. (only if no pex is involved) Also close the balancing valve most of the way on the termovar to ensure that there is not too much mixing there. However, sounds like most of the problem is insulation. Address that asap and see if it makes a difference. Good luck!

 

[henfruit]

why did you say only if no pex was involved? we all use pex.

 

[WoodNotOil]

why did you say only if no pex was involved? we all use pex.

I believe most pex has a 180* temp limit. I though that is perhaps why he was running around 170* instead of the typical 180*.

 

[Piker]

Most (not all) pex is rated 180* @ 100psi... 200* @ 80psi... as the temp goes up, the pressure rating goes down. Most hydronic systems pressure relieve at 30 psi.

I have 180* water running through a pex - Ultra fin zone in my house pretty consistently. Temps to 190 are seen at times. No problems as of yet, and don't expect any. I even use the hotly debated "shark-bite" connectors that some guys just refuse to use.

cheers

 

[muleman51]

I'm not even on a Tstat all. Just running full bore to the storage tank and that's all I get for heat. There is no pex involved to the storage tank. The termovar should shut down to maintain its temp on its own. The isulation is on its way.

 

[WoodNotOil]

The termovar should shut down to maintain its temp on its own.

"Should" being the key here. Tarm suggests closing the balancing valve 1/2 to 3/4 of the way to get the termovar working properly. If yours is wide open, then too much hot water is likely circulating and causing the boiler to idle. Also, If your circ to storage is always running the tank temp may drop as your boiler temp drops losing heat. Many here are experiencing that and are trying to find ways to better control the loading of storage like by using the tekmar 156 for instance.

 

[muleman51]

There is no idle. I'm not using a tstat at all. the boiler burns constantly. If the termovar isn't shutting down and allowing too much hot water to pass, the boiler should get even hotter. So my question still is how much delta can you expect. Is 25-30* all you can get in one pass and if you should get more why is my boiler not doing so. I insulated the tank again yesterday, now have 18" on top, didn't seem to help much.

 

[hoth2oguy]

I would say that 25-30 degree delta T is not bad. 1" pipe may be a bit of a bottleneck if your boiler is rated at significantly higher than 100k BTU. A larger pump may increase the delta T. All that being said, most boiler systems are designed around a 20 degree delta T so I think you are doing about as well as you want to. If you are sending water to the tank at 180F and it is coming back at 150F that is about as good as you can do - remember, the Termovar is not going to let return temps drop below 140 anyway. Given that you have pressurized storage, I would suggest that a boiler set point of 185F or even 190F would allow for higher tank temps, more heat stored and better Delta T. Hope this helps,

Chris
BioHeatUSA sales guy

 

[muleman51]

There is no set point, I do not have a tstat hooked to the boiler, only a timer, just like a Garn. Burn full tilt until the fire goes out or timer shuts down. If the pipe were too small or the pump not large enough, that would create an overheat problem and give me more delta, but if 20-30* is all I can expect, I'm just using all the heat the boiler puts out and it's undersized.

 

[Jersey Bill]

An undersized boiler is an efficient place to operate. "Undersized" is relative to your heat load and storage load (storage size). If you can't get your storage up to your operating point however, then the boiler is too small.
A large delta T could indicate 2 things, either the boiler is at max capacity (good) or low flow (bad), or both. Generally I try to keep the delta T as low as possible.
Assuming that the boiler is about at max capacity, if you increase the flow rate, then the delta T will drop. This will lower the average heat exchanger temperature and increase boiler output.
I don't like the termovar valves because the pressure drop through the valve is always there, which will tend to reduce flow. I use a 3-way ball valve to maintain minimum boiler temperature. When the valve is not mixing the port is wide open with very little pressure drop.
I would try to get that delta T down.
What is the nameplate boiler output, and design heat load for the house?
Do you have an idea of how much boiler flow that you have ?

 

[WoodNotOil]

There is no set point, I do not have a tstat hooked to the boiler, only a timer, just like a Garn. Burn full tilt until the fire goes out or timer shuts down. If the pipe were too small or the pump not large enough, that would create an overheat problem and give me more delta, but if 20-30* is all I can expect, I'm just using all the heat the boiler puts out and it's undersized.

A timer (IMHO) is not a good way to control the circ as burn times vary and you are most likely drawing down the storage temp at the end of the burn cycle. To start with crank the boiler up to the 180-190* degree range and that should help raise the storage temp. Next think about getting something like the tekmar 156 to control the loading so that you get the best charge possible. Once you do those things if the boiler runs without idling and you are still not happy, then perhaps the boiler is undersized. How is your adobe holding up? All the chatter on here about being ripped off by the guy selling them gave me the impression they didn't work. (although I didn't read all the posts about them)

Edit: I just reread your last post and think I misunderstood. Are you saying your draft fan is controlled by the timer or your circ? If it is your draft fan then disregard my first suggestion above.

 

[muleman51]

Yes , you finally got it. There is no set point to raise. The boiler doesn't idle it runs full bore until the timer stops. I set it for 4-6 hours depending on the load and what I'm burning. Usually there are just enough embers to light the next fire. No idle time and all the heat I get is 170 off the boiler and can't get the storage up to temp. The Adobe is not holding up well but I am trying to make it work. If I had money I'd junk it but I don't so I keep fooling with it to try to get by. I bought and paid for a larger unit but was shipped this one and can get no response from Adobe to resolve the matter.

 

[chuck172]

"I bought and paid for a larger unit but was shipped this one and can get no response from Adobe to resolve the matter."

Thats your problem right there!

 

[muleman51]

You're right! I know thats one of the problems. But the basic design is proven, I just need to work out the details, other than it's just too small.