Return water temp. makes no sense ?

[Dino57]

Finally put a temp gauge on my return line from the side arm and heat exchanger It is returning a little cold at 135 f with the boiler putting out 180 f I am running 125 ft of pex, 75 ft barried 50 ft in house. going to insulate pex in house to stop heat loss.
Had the boiler cycling the other night when temp was -24 C in Ontario. The boiler damper would open for 6 minutes and then close for 3 minutes .This was constant for over 2 hours of watching it work.The damper would close at 180 then open at 170 F

What makes no sense to me is the water temp.will rise to 145 f slowly while the damper was closed When the damper opened and the supply temp start to rise the return line temp will drop as the water got hotter.I am useing a taco 008 pump

Any Ideas.

Thanks

 

[jebatty]

Can you provide a diagram of your plumbing? and show where you are measuring temps? size of pex/piping, distances, etc. It is a little difficult to get a mental picture without more info.

I looked at the Green Horizon website. It indicates gasification technology with quite a different combustion design than other gasification boilers I am aware of. How long has yours been in operation? Any more info you could provide on your experience?

 

[sdrobertson]

I looked at the Green Horizon website. It indicates gasification technology with quite a different combustion design than other gasification boilers I am aware of. How long has yours been in operation? Any more info you could provide on your experience?

This looks like a Seton design.

 

[Dino57]

I will try to figure out how to post a diagram. the system is a basic closed loop . the temp is taken right at the boiler inlet and outlets with in water gauges. the water runs to a side arm exchanger on the domestic hot water tank then over to a heat exchanger in the plenum of the oil furnace then back to the boiler the run is 125 ft each way.. There is no storage and only 7.5 gallons of water in the boiler tubes..Have been using boiler for just over a month,had to change some plumping yesterday but at the extreme cold last week was able to maintain 70 degrees in house.Still have some work to do to prefect the system but looks good so far.Heat temp at vents with the wood boiler is 114 degrees and with oil furnace running is 121 degrees

Have a feeling I need a different pump with more gpm.The pex is 1 inch and the heat exchanger is 19 by 20 inches rated for max 120000 btu at 15 gallons a minute and 189 degrees.

Thanks

 

[jebatty]

My gut reaction is that with 1" pex, you're basically looking at 8 gpm's maximum flow rate, which at a 20 degree temp drop (supply-return) = 80,000 max btu transfer. With a water tube design, my guess is that your boiler is heating water faster than the heat is being drawn off; causing the damper to go through close/open cycles. You need to increase your water flow rate; and to do that you need larger piping with the proper pump. You probably can force more than 8 gpm's through a 1" pipe, but your pump head will increase significantly as flow increases. I'm no expert to do the calculation of head at higher flow rate. 1-1/4" design is 14 gpm's = 140,000 btu's; 1-1/2" design is 22 gpm's = 220,000 btu's. It seems off-hand that one of these or equivalent should be your design target.

 

[steam man]

From experience working with industrial processes I would say your system has some typical problems with some "lag" in temperature measurements maybe due to long pipe flows. Typical on-off processes will tend to cycle like this. Make sure your pipes are all insulated.

The more I read about the problem your having the more I think that the flow rate may be the problem. Kind of a balance/flow rate/load issue. It doesn't sound like the system has enough flow to keep the boiler loaded up thus the cycling. This is where a variable speed/multispeed pump may help. But that depends if your already maxed out on the flow through the size of pipe your using.

Mike

 

[atlarge54]

Dino57 do you have any provisions for loss of electricity? Those Seton style boilers look like a brief period of no circulation could be a real problem.

 

[Dino57]

Steam Man I think you are right it is lag time.It takes about 3 minutes to push the water from the boiler to heat exchanger then back to the boiler.app. 6 gallons a minute flow I am going to pick up a 3 speed pump next week to up the flow and that should keep the return temp. above the 140 target.

Thanks

Atlarge54 Yes I have a 1000 watt inverter/charger for power failures that automatically switches on.Also have a normally open motor valve plumped in to a cast iron rad to act as a dump zone.If the power goes of or temp. in boiler reaches 200 degrees the valve opens.The inverter powers pump,damper and dump right now .going to change it so it only powers pump.That way when the power goes off the dump zone will open and the damper will close. Then the pump will still run and disperse the heat.

Dino

 

[atlarge54]

What brand of inverter? Have you run a power off trial of your backup yet? What do you have for batteries? I should be getting a Tripplite 700W unit in the next day or two. We just had another power outage the other night and I'd like to sleep through the next one.

 

[Dino57]

atlarge54

The inverter is a Xantrex Freedom Hf /1000. It is made for boats and rv's.Seems to be alright on the boiler and I calculated 2 hr of tjme .I use a deep cell battery. It ran a light bulb for 9 hrs.Have not ran the boiler on it for more than 10 minutes and battery was still at 12.1 volts and staying there.

Dino

 

[jebatty]

If you have 6 gpm with an 008 (60,000 btu at delta-T=20), then you have about 12 feet of head based on the 008 flow chart. A Grundfos multi-speed UPS 15-58 will get you practically no improvement in gpm at 12 feet of head. If you wanted to double the double the flow to 12 gpm (120,000 btu at delta-T=20), then head will increase approximately by a factor of 4 [experts correct this if wrong], and without spending mucho bucks, you're not going to find a pump that will handle 48 feet of head.

It still appears to me that you have a design problem related to 1" pex being undersized for want you want to acheive.

 

[Gene C]

In your explaination of how the system flows, you indicate that it goes to a sidearm and then to a plate heat exchanger. Are you going "thru" the sidearm and then to the plate exchanger? What size is the sidearm inlet? Most sidearms that I have seen are 3/4" which would really reduce your flow. If this is the case, then you really need to make a few piping mods to minimized the flow reduction. Possibly install a tee just prior to the sidearm and run the sidearm and heat exchanger in parallel and then rejoin to the return line after the exchanger.

 

[Rickard]

Another possibility comes to mind, as it is a problem I experienced. I have a Termovar mixing valve on my wood boiler and it doesn't close all the way even when the boiler is at full temperature. The Termovar was mixing too much return from the boiler and the boiler was getting to the high temp idle without throwing enough heat into the system. I missed it on the first install, but apparently it is in the design, and the company recommends a valve before the boiler return inlet on the Termovar to regulate that flow. This was causing a low return temp, as you are describing. I don't know if this is at all related to your issue but I thought I could throw that out.

Dean