setback on Outdoor reset

Wayco Wayne_2

and got no response. I figure everyone was too full of Turkey and asleep in front of the football games to answer. I installed a Buderus with a logomatic control. The Homeowner has a night setback tstat on one zone that he put in himself and he thinks very highly of. Of course the Logomatic has outdoor reset and sets back the water temp at night so the recovery of the zone in question will not be very fast. I was told by Mike at TekMar that it is always better to set back the water temperature rather than the tstat. How do I explain to the homeowner the difference and benefits of doing it this way? Thanks in advance

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eleft_4

Reset

It's the difference between three steps on the front entry and the flight of stairs to get to the second floor.

It's the difference in their heart rate upon entering the home, or going up the stairs to the upper floor.

Relate the boiler recovery to this activity.

al

Wayco Wayne_2

An interesting

way of looking at it. I just thought of another example. Since turning the water temp down 7 degrees the system is still emmitting heat and the surrounding space being heated doesn't totally cool off and get cold. It's like leaving the engine idling on a car so you don't have to warm it up in the morning. WW

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Steve_35

We recommend NOT using a setback with water systems

Setbacks in upstate NY seem to be the number 1 cause of pipe freezes.

Think about how a water system operates. As it gets colder the water is moved through the system at longer intervals and isn't moving (when there's no call for heat) at shorter intervals. As we approach design temp (we use -10º)the water moves through the piping continuously. That goes a long ways toward preventing freezing.

Now the house is nice and comfy and the piping is hot and the setback kicks in. The water stops flowing. Maybe for a couple of hours at sub freezing temps. You get the picture.

Lowering the water temp lets the house cool down but the water still flows through the system. Much less likely to freeze on design days or high wind evenings. But then we never get high wind on cold nights.

Steve_35

We recommend NOT using a setback with water systems

Setbacks in upstate NY seem to be the number 1 cause of pipe freezes.

Think about how a water system operates. As it gets colder the water is moved through the system at longer intervals and isn't moving (when there's no call for heat) at shorter intervals. As we approach design temp (we use -10º) the water moves through the piping continuously. That goes a long ways toward preventing freezing.

Now the house is nice and comfy and the piping is hot and the setback kicks in. The water stops flowing. Maybe for a couple of hours at sub freezing temps. You get the picture.

Lowering the water temp lets the house cool down but the water still flows through the system. Much less likely to freeze on design days or high wind evenings. But then we never get high wind on cold nights.

Steve_35

We recommend NOT using a setback with water systems

Setbacks in upstate NY seem to be the number 1 cause of pipe freezes.

Think about how a water system operates. As it gets colder the water is moved through the system for longer intervals and isn't moving (when there's no call for heat) shorter intervals. As we approach design temp (we use -10º) the water moves through the piping continuously. That goes a long ways toward preventing freezing.

Now the house is nice and comfy and the piping is hot and the setback kicks in. The water stops flowing. Maybe for a couple of hours at sub freezing temps. You get the picture.

Lowering the water temp lets the house cool down but the water still flows through the system. Much less likely to freeze on design days or high wind evenings. But then we never get high wind on cold nights.

jerry scharf_2

how about this

WW,

help him make the trade off.

it's a three way tradeoff to be made. The outdoor reset saves money at the boiler and increases the comfort in the heating system. The setback saves on the amount of heat needed for the zone. The compromise is that when you come out of reset and want to heat the zone back up, it will either take a lonng time or you have to reduce the amount of reset savings.

My best analogy would be sizing a car engine. A car running on the highway doesn't need a lot of power. Stop and start takes more energy, like the lower city milage for cars. To be able to start more quickly, you need a bigger engine. The bigger engine will use more fuel all the time (even idling) to allow for the faster starts. (Of course, you are saving with setback unlike city driving, but it will help the picture.)

The most energy savings would be from close reset and setback, but the recovery may take a couple hours. He could always set times on the reset to include the recovery time. If he wanted it warm at 7am, start the recovery at 5AM. You can also run the reset curve just a bit lower than optimum and shorten the recovery time.

Also, since the reset is on one zone the trade off is even more toward outdoor reset.

hope this helps,
jerry