At what speed do you keep your pumps? I have had mine set on the medium speed through the milder weather but,last night,the Outdoor furnace couldn't keep up. I'm thinking I need to run it on high now it's colder.Also,ave been getting along great with water temp at 165.Search on here makes me think 180 is probably where I should be.
At what temp does the water arrive in your house? If you are not losing temp, you have a choice of raising the temp at the boiler or increasing the number of radiators in the house. I could see where a faster speed on the pump would work if you were losing a lot of heat on the way to the house. I don’t use an outdoor boiler. Just seems to make sense.
A higher speed is going to deliver more BTUs to your heat exchanger. Making up some numbers here, on medium speed let's say water enters at 165 and leaves at 135. Everything else being equal, high speed is going to make it enter at 165 and leave at 145. You now have more "hotter" water in your HE at any given time. Again, those are made up numbers, but the concept holds true. I have a 26-99 on my main loop that I usually run on medium, but when it gets real cold I kick it over to high. I have thermometers on my entry and exit (entry to house, exit from house). With the speed on high, given the same heat load, my exit temps are higher....and my overall system temp usually mirrors my exit temp. Cranking up the pump raises my water temperature I'm circulating through the house. I run a 160 - 180 low/high on my boiler.
OK. There is that school of thought. Heres another. The slower the pump speed, the longer that hot water stays in the heat exchanger and the more heat transfer occurs. I wouldn't want to use just a little bit of the heat available from the water temps of entering leaving heat exchanger; I want to maximize the heat transfer. Kind of like a furnace blower motor. If you want more heat, bump it up to high? or slow it down and allow the air to pick up more heat from the exchanger as it passes across it?
I would also like to add that my circ pump is not a multi-speed, so take that as no real world experience regarding actual results.
I don't think that holds true. I think you slowed down the flow of cold air/water on the other side of the HE, you might end up with higher temperatures....but overall less BTUs/hour being exchanged. Slowing down the hot side means there are less BTUs/hour available to be exchanged. Cranking up the blower on your fan motor will make the air feel cooler because it spends less time going across the HE, but there's more air flowing....overall more heat being exchanged. Think of it this way....if you wanted to cool off the radiator in your car, would you want a fan blowing on it real slow...or real fast? If you used a slow fan, the air coming out of the radiator would be really hot....and the fast fan not as hot. But the fast fan is going to cool down the overall temperature quicker than the slow fan.
lukem. Your explanation makes sense. If the difference in pump speed doesn’t give enough additional heat, then I suppose it is time to move on to another method. Of course a higher water temp would require more fuel due to added heat loss whereas an additional heat exchanger in the house would allow the user to continue to operate at a lower temperature but would require an investment in infrastructure. The other option is to address insula and air sealing if the house.
That is the school of thought that my Dad had. I go along with his thinking on boilers because he probably knew more about boilers than anyone else on the planet.
Having a pump too fast will cause the return temp to be too high and short cycle the boiler....that's probably why he thought that...and it is correct. With an OWB (or anything with storage) that doesn't matter.
I can certainly see where higher water temps would give more heat.I guess I'm still confused about the speed.In my case,I have a plate heat exchanger to go into a hot water system.It's set up so my oil furnace pump does the inside of the house and the boiler pump just moves water from there and back.Would a slow speed allow more heat units to be gathered by the plate exchanger ?
Try bumping your high temp limit to 180 and the bottom limit at 165/160. The house should be able to withstand a cold front much easier.
I run mine at 180 with a 15 degree differential (fan kicks on at 165, off at 180) during the winter. Fall/spring I bring it down to 160 or so. Even at 180 the main part of my house will get a little chilly when the outside temps really drop, say single digits and below...though no fault of the boiler. The house is newer construction/well insulated but its a large open space with high ceilings, we have a LOT of windows surrounding the space, and we also have open steps leading down into the unheated basement...so between all that it can get a little cool. Thats when we kick on the pellet stove to help out a bit.
