Good morning. The weather is finally turning cold – it is 4° below zero this morning. I have been running my circulator pumps off my Garn 2000 on the middle setting of three speeds while the weather was in the 20s and 30s. The house is cool this morning and the temperature difference between supply and return temperatures on the boiler have widened. It’s sort of makes intuitive sense to increase the pump speed and therefore the circulating volume to maintain a high temperature at the heat exchanger in the house. I think correctly? Does this make any sense? I increase the speeds on the pumps this morning so I will see what happens. thanks!
Pump speed when it gets cold
- Thread starter mynx
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cumminstinkerer
Burning Hunk
maple1
Minister of Fire
sloeffle
Minister of Fire
Yes, it makes sense.
I have temperature gauges on the heat exchanger in my furnace. On low I was seeing about a 20° drop across the HX, medium ( which I'm currently running ) I see about a 17° - 18° drop, on high I see about a 15° drop. My furnace fan speed is adjustable, and I haven't found changing it really matters one way or the other.
With my plate exchanger for making hot water, and furnace together on low I was seeing a 35° drop. That's some serious BTUs.
I have temperature gauges on the heat exchanger in my furnace. On low I was seeing about a 20° drop across the HX, medium ( which I'm currently running ) I see about a 17° - 18° drop, on high I see about a 15° drop. My furnace fan speed is adjustable, and I haven't found changing it really matters one way or the other.
With my plate exchanger for making hot water, and furnace together on low I was seeing a 35° drop. That's some serious BTUs.
sloeffle
Minister of Fire
Yes, that's what I come up with at 3GPM. At 4GPM you are close to 70k BTU.
Boiler is pretty close to the house with very little head loss. I'm not sure exactly how many GPM's I'm pushing.
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The new ECM pumps are pretty slick and most come with built in programs. I saw one that controlled speed to temp differential between supply and return.
cumminstinkerer
Burning Hunk
I have adjusted speeds on my storage to load loop but really see very little change, medium on a 15-58 seems to work the best, I only have 130' of 1 1/4 (equivalent) between my HX and my Storage, the storage loading circ is a 26-99 with about 40' of the same size pipe and it seems to run better with it on high speed. I have played around with different speeds and that is what I've found to work best. I am not changing speeds on the 26-99 right now because the switch is giving me fits and I havent found a work around.
PassionForFire&Water
Minister of Fire
Each boiler has a maximum heat exchange (BTU/hr)
Does not matter if you overpump
The manufactuer Garn, can tell you what the maximum gpm's are for each of their boiler models
If you overpump, your delta T will go down
BTU/hr = 500 x GPM x dT
(dT in difference Farenheit between Supply Temp and Return Temp)
GPM = BTU/hr / (500 x dT)
if GPM goes up, dT needs to go down because it's the denominator
dT = BTU/hr / (500 x GPM)
if dT goes up, GPM needs to go down because it's the denominator
For cord wood boilers important factors are:
- Moisture content of your wood
- how full is your firebox; a full firebox will give you maximum heat output, after 2 hours of burn it will be less than at start
- Return water temperature; again boiler model specific
Does not matter if you overpump
The manufactuer Garn, can tell you what the maximum gpm's are for each of their boiler models
If you overpump, your delta T will go down
BTU/hr = 500 x GPM x dT
(dT in difference Farenheit between Supply Temp and Return Temp)
GPM = BTU/hr / (500 x dT)
if GPM goes up, dT needs to go down because it's the denominator
dT = BTU/hr / (500 x GPM)
if dT goes up, GPM needs to go down because it's the denominator
For cord wood boilers important factors are:
- Moisture content of your wood
- how full is your firebox; a full firebox will give you maximum heat output, after 2 hours of burn it will be less than at start
- Return water temperature; again boiler model specific
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This is very helpful. Thank you. My thinking is to maintain the highest temperature at the heat exchanger to facilitate maximum heat transfer. My boiler delivers hot water from a separate building to a heat exchanger in the house and the loop on the other side of the heat exchanger supplies, the zones in the house. It seems that a lower GPM will reduce the temperature across the heat exchanger and diminish the heat transfer capacity. Is this logical?
I put my Garn 2000 in 2009. My four heat exchangers are in my Garn barn. Two run my shop one for the furnace and one for the floor heat. Have two that run two 450 feet loops to my house to run three furnaces and my domestic. I run antifreeze on the secondary side of the heat exchangers. So with all that said I have a lot of pumps and have played with speeds a lot and it seems on my set up the medium speed works the best in all temps. I do run my filter pump on low speed. It runs 24/7 all my other pumps only run when there is a call for heat.
sloeffle
Minister of Fire
Based off of your experience. Do you think turning them off and on has a negative effect on the life of the pump ?
I have twelve pumps on my system. The 24/7 pump has only been running a few years as I installed the filter after the first leak. I had to replace four out of the twelve. Two during the first year on the antifreeze side both leaked and were warranty. I have replaced two on the primary side one after the first leak when the system had set with no water in it for a while and I replaced one the other day on my floor heat system primary side. So I don't feel cycling the pumps on and off has hurt them. The only time my system has been completely down was when I had the two leaks otherwise I heat my domestic year around with the Garn.
salecker
Minister of Fire
What make were the pumps that were failing?
I have 14 years on all my Grundfos pumps, one is the smart unit that learns your needs and pumps accordingly.
I have 14 years on all my Grundfos pumps, one is the smart unit that learns your needs and pumps accordingly.
The two that leaked were Taco's. They were replaced with Grundfos. The other two that failed were Grundfos. All twelve are currently Grundfos three speed pumps. Two different sizes.
What size plate exchanger are you using? Also, do you have it heating the water in your water heater?Yes, it makes sense.
I have temperature gauges on the heat exchanger in my furnace. On low I was seeing about a 20° drop across the HX, medium ( which I'm currently running ) I see about a 17° - 18° drop, on high I see about a 15° drop. My furnace fan speed is adjustable, and I haven't found changing it really matters one way or the other.
With my plate exchanger for making hot water, and furnace together on low I was seeing a 35° drop. That's some serious BTUs.
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