Heating with hydronics

[alvanko]

I know this is way off base as far as tractor related questions, but, I didn't want to join a new on-line forum to ask 1 question.
I'm sure there are a few heating and cooling experts somewhere on this forum and a few who have hot water heat in their homes.
I have hot water heat in my 140 year old farm house. Love it. Every year in the fall I clean the water supply filter/regulator, purge air from the system, etc...
I had a 3 speed Grunfos circulator pump for 10+ years and the past couple of years I have had to get it to start to pump my manually turning it with a screw driver. Runs OK after I get it started. This year I replaced the pump as a precation. 10 years old you know. The old pump was 3 speed and so is the new one. I ran the old pump at "high" speed. #3 setting.
Question:
What is the right speed I should be running this pump at?
It is a single loop system. No seperate room controls. Just basic loop. 2 story home. What do you think?

 

[Egon]

Seems I have a similar situation but only two speeds.

The fellow servicing the furnace said it probably would not matter in my case. However, mine is set at the fast speed. I would assume that the more volume goes out the less chances of one radiator getting starved as they are hooked in parallel.

For a proper determination it would probably require some empirical tests using temperature senors to make sure all radiators are getting sufficient water flow.

Note: palm of hand will seve as temperature sensor.

And that is my guess.

 

[Highbeam]

The faster the water moves, the more electric you will consume but you also might get more noise and cavitation. The water needs to move slowly enough that it can give up heat to the rooms.

 

[yankeerider]

You can run it at the lowest speed which gives adequate heat. Trace the system, and decide which convector(s) are the last in the loop before the water returns to the boiler. That is being fed the coldest water, and if the heat is okay there on the coldest weather days, the pump is running fast enough. Too fast won't do any harm except cost you more than necessary in pumping costs, and possibly noise.

 

[kenmac]

I had that type (b-4 I went with a 90+) I only had a single speed pump motor inside the air handler. You don't want the water moving so fast that you don't get all the heat out of the water. I would say low speed. On heat cycle the blower speed should also be on low speed. Some run med. speed

 

[zuiko]

I would probably start out on low and keep an eye on the temps of the rooms at the end of the line in the dead of winter. If they seem cold, increase the speed. I've never had pumps with more than one speed, so it was a pretty easy decision for me .

 

[Egon]

On our system one can not hear the pump when it is in operation! High or low speed. One can hear the burner in operation though as well as the stack heat recovery fan.

As for electric consumption costs between high and low operation it is very doubtfully if it could be noticed on the Hydro bill. Just thinking about it it would seem that at a sufficiently high pump speed flow would be constricted and the effective current draw would be reduced.

 

[alvanko]

Thanks for all the replys. I'm still not sure. I wonder if the lower the speed the higher the pump lift capacity (2 stories 20' lift). I always ran the old one on high with no trouble but maybe I'll try this one on medium. I used to be able to hear the old pump when it ran but the new one is quiet and I can't hear it.
I never thought about the cavitation thing. Boiler has been noisy the past 2 years (gurgle & pop).
The last thing I need trouble with in the winter is the furnace/boiler.

 

[SpringHollow]

Going fast does not limit your ability to transfer heat. It would actually increase it.

Ken

 

[RonMar]

"getting all the heat out of the water" is not really all that important, not like it is in an auto radiator where you are trying to move heat from an engine to the atmosphere. You are not trying to remove heat from the boiler, you are trying to add heat to the house. Heat transfer from a radiator to the air is a factor of heat difference. The faster you pump the water, the more hot water is delivered and the higher the overall radiator surface temp is maintained which equals greater heat transfer into the room. In a heating system, heat not removed from the water is just returned to the boiler to be re-distributed to the radiators on the next go around... In fact a slower flow will have less turbulence, and turbulence is your friend when it comes to heat transfer as it helps break up laminar flow along the surfaces that leave a stagnant layer of water to insulate like the thin layer of water held against the skin in a wet suit.

As mentioned, the lowest pump speed that still maintains adequate radiator temp will be your most efficient.

My FIL gave me a 3 speed Grundfos pump and when I started playing with it, it would not run. It seems that setting, even when the system was drained, left water in the lower half of the pump housing. This water corroded the cast body and caused the pump to sieze. I was able to disassemble the cartridge assembly and clean it throughly and it now works fine...