Effects of slowing/speeding up circulator pump

[ikessky]

Maybe I'm just missing it here somewhere, but my searches aren't coming up with what I'm looking for.

From what I can see, you are looking for a 20* difference between the inlet and outlet on a radiant heat system. With a 3 speed pump, I'm assuming that this can be tweaked by increasing or decreasing the speed of the pump. Am I right in assuming that you increase the difference by speeding the pump up and decrease it by slowing the pump down?

 

[Alchymist]

Backwards - slower pump speeds means the liquid is in contact with the "radiator" surfaces longer and transfers more heat, thus increasing the inlet/outlet differential.

 

[CARS]

I was told the difference is suppose to be <10 degrees.

Mine, on good days, is less than 5 degrees.

 

[ikessky]

With a flash heater or tankless heater, wouldn't you want a higher differential? I mean, a tankless heater is designed to take what, 50* water?

 

[Alchymist]

With a flash heater or tankless heater, wouldn't you want a higher differential? I mean, a tankless heater is designed to take what, 50* water?

He's talking about radiant heat, not tankless heaters. Putting a hot water or water/antifreeze into a heater - (radiator, in floor piping, whatever) and returning a cooler water to the boiler/heat source.

 

[ikessky]

Sorry, I should have clarified a little better. I have a tankless heater. Being that it is designed to take like 50* water, wouldn't I want a little larger differential? Seems like 100-110* water coming back into it would take it out of it's efficiency range. Then again, it's a modulating burner.......

 

[stingry]

With a flash heater or tankless heater, wouldn't you want a higher differential? I mean, a tankless heater is designed to take what, 50* water?

If you maintain a higher differential, most of the heat transfer will be at the beginning of the loops and these areas will be warmer than the end of the loops.


Cheers
Steve

 

[BigWil]

I just had my hot water radiant boiler replaced with an electric one. I was talking to the installer, who also put in a much faster pump (46gpm instead of 12gpm) The warmer the water when it returns, the less work it is to maintain that heat. I went from paying $500/mo on oil to $270/mo on electricity...and I removed all heat from the basement while renovating it. The installer said he had someone tell him not to replace his existing pump with the 46gpm pump, and the guy called him back the next month...the new pump made over $150/mo difference on the electricity bill.

 

[tdkkart]

There's an issue here. While speeding up the pump to lessen the temp differential across the floor will indeed cause the heater to have to raise the temp less, how many more gallons does the heater have to heat??
It all works in a continuous cycle, a gallon of water is heated and sent to the floor where the heat is removed, that gallon then gets returned to the heater where the cycle starts over. If you speed the water up so that you have 1/2 the temp drop, you have to deliver twice as many gallons to deliver the same amount of heat to the floor.
I'm sure there's a balancing point, if you have enough super sensitive thermometers and flow meters you'll be able to figure it out.

 

[curiousB]

I just had my hot water radiant boiler replaced with an electric one. I was talking to the installer, who also put in a much faster pump (46gpm instead of 12gpm) The warmer the water when it returns, the less work it is to maintain that heat. I went from paying $500/mo on oil to $270/mo on electricity...and I removed all heat from the basement while renovating it. The installer said he had someone tell him not to replace his existing pump with the 46gpm pump, and the guy called him back the next month...the new pump made over $150/mo difference on the electricity bill.

I think Canada enjoys some of the lowest consumer electric rates in the world. Here in IL electric is 3.5X more expensive for the same BTUs as natural gas. I'm not sure the ratio for oil but I suspect oil is still cheaper than electric for apple/apple BTUs comparison.

 

[BigWil]

I think Canada enjoys some of the lowest consumer electric rates in the world. Here in IL electric is 3.5X more expensive for the same BTUs as natural gas. I'm not sure the ratio for oil but I suspect oil is still cheaper than electric for apple/apple BTUs comparison.

I wasn't trying to push him into an electric boiler system, I was trying to explain that a higher speed circulation pump would save him money. If I had stuck with oil, and just changed the circulation pump, I would have saved a lot of money on oil.

 

[tdkkart]

I wasn't trying to push him into an electric boiler system, I was trying to explain that a higher speed circulation pump would save him money. If I had stuck with oil, and just changed the circulation pump, I would have saved a lot of money on oil.

Please explain how a larger pump reduces the number of BTU's required to heat the building..........

 

[Zick]

I wasn't trying to push him into an electric boiler system, I was trying to explain that a higher speed circulation pump would save him money. If I had stuck with oil, and just changed the circulation pump, I would have saved a lot of money on oil.

Can you tell us how much your paying for Oil/gallon and for Electric/kwh?

 

[BigWil]

Please explain how a larger pump reduces the number of BTU's required to heat the building..........

Since I'm not familiar with BTUs etc, I'll try to explain it differently. The hot water transfers heat into the slab, or in my case, the radiators. By having the water circulate much faster, it returns at a higher temperature. It takes much less energy to warm up the water 3-5 degrees than 30 degrees. Also, without the large temperature drop, the heat is much more even throughout the building, meaning that you don't have cold areas, which could wreak havoc with the thermostat settings. My house is now much more evenly heated, at a reduced cost.

Can you tell us how much your paying for Oil/gallon and for Electric/kwh?

I was paying around $1.39/L ($4.91/Gal), electricity is 10.5cents/kWh

2571 kW vs 101 Gal of oil.

according to this, http://www.americandistributing.com/heatfuel.html I'm ahead. Oil was about 14,007,690 BTUs of energy used vs 8,774,823 BTUs of energy used.

 

[curiousB]

The first law of thermodynamics refutes this. Energy used to fire the boiler is either distributed to the room or lost up the chimney. It just can't disappear. Either the energy is going up the chimney or into the slab.

The faster pump speed could have the opposite effect you suggest because the heat returning to the boiler is higher and as such the boiler cannot impart as large a temp rise. Therefore more heat is wasted up the chimney.

 

[Alchymist]

Since I'm not familiar with BTUs etc, I'll try to explain it differently. The hot water transfers heat into the slab, or in my case, the radiators. By having the water circulate much faster, it returns at a higher temperature. It takes much less energy to warm up the water 3-5 degrees than 30 degrees. Also, without the large temperature drop, the heat is much more even throughout the building, meaning that you don't have cold areas, which could wreak havoc with the thermostat settings. My house is now much more evenly heated, at a reduced cost.

While what you stated about the water returning at a higher temp is true, the faster the water is circulated, the less heat is transferred to the slab or radiators. In any given system, there will be an optimum speed/transfer balance, and it will depend on boiler BTU input, size of radiator, and desired temperature. This is the reason the load calculations have to be done.

 

[BigWil]

I guess that is the advantage of my electric boiler. No heat loss out the chimney, as there is none. My boiler kicks in with a very small temperature difference, and has 4 elements, each of which draws 25 amps. It really only uses the one, and if it goes, the system just starts using the next one.

Alchymist: I agree with you. There is an optimum, I still don't know if my system is the absolute most efficient it can be. However, I do know the higher GPM pump is much more efficient than the 12GPM pump.

curiousB: I know the energy was going somewhere. What was happening was more energy out the chimney, and because of the slow circulation speed, more energy was being dumped into certain rooms instead of even heat throughout the house. This would cause the thermostat to call for even more heat as it was in a colder area of the house.

I am not guaranteeing these results for anyone else. I am saying in my personal experience, too low of a speed on the circulation pump will be costly.

 

[Baada]

The first law of thermodynamics refutes this.

I second the thermodynamics laws here and have a 1850 page book to prove it. (Not saying I was awake for every lecture that semester though)

Every heating device (electric, natural gas, propane, used oil, wood, etc) has a very specific point where it acheives it's highest efficiency, which is where you get the most heat for least amount of fuel used.

Every heat distribution device also has a very specific point in which it operates at peak efficiency. In this case, the flow rate at which heat is equally distributed to the entire floor. To slow and the heat only goes into the floor where first portion of the piping runs. To fast and the floor doesn't get any warmer than it already is, or worse, gets colder.

And then there is the environment. To maintain current temperature, a perfectly efficient system would add exactly the same amount of heat that was being lost by the environment at exactly the rate it was being lost (obviously doesn't exist).

When you take the heating device and combine it with the heat distribution device into one system, the highest system efficiency may, or may not, be the point at which each device is running at it's own peak efficincy. A perfect design would be when the systems peak efficiency is the point at which each unit is operating at it's own peak efficiency. When the design is less than perfect (always true in the real world to some extent), the systems peak efficiency will be at a point where one or more of the devices are not operating at it's own peak efficiency. This is a concept often misunderstood by people designing systems because they simply use the literature provided by each component's manufacturer and set the device to run at it's most efficient level not, taking into account the interaction of the components and the environment.

He saw the performance of the system increase because he altered his system to a more efficient operating point. Somebody else with a different system and environment may need a reduced flow rate to get better results.