Comfort vs Efficiency

mark ransley

If after taxes and all, you really pay that little for electric than I would not be suprised if at times heating with electric would be cheaper for you. You should compare energy costs.

BMac

Hello,

I am just a homeowner who has periodically perused your forum over the last couple of years. I have a 1920's house with hot-water rads in the Toronto area. They are hooked up to a Vitola NG boiler with a Vitotronic control with outdoor reset. The pump for the main heating circuit is controlled by a thermostat upstairs. I have left the controls basically on default since it was installed 2 years ago and I have been trying to get a bit more efficiency out of it this year. For this experiment, I have basically tied the pump in an always on mode by cranking the thermostat upstairs - I figured this was the best way to figure out the proper water temperature/heating curve setting for my house.

I have read somewhere on your forum that the lower the water temperature, the better the efficiency. This winter I have slowly been lowering the water temperature and I currently have it at 11F less than where I started (which I think means the rads are way oversized). In this situation, the house is warm enough on the coldest days, plus these relatively warm days we have recently been going through.

The problem comes when I try to have the temperature change for sleeping or when we are out of the house. It takes a long time for the temperature to drop (2 hours), and an even longer time for the temperature to get back to normal (4 hours or so). Previously, with the water too hot, the upstairs thermostat could control these temperature fluctuations much more quickly.

Getting the temperature to drop quickly is not really the problem - I can easily put the thermostat back in the picture and get it to shut the pump off for a while when I want the temperature to drop. However, getting the temperature to go back up in a reasonable amount of time is the problem - with the lower water temperatures it is just going to take longer even with the pump constantly running.

The lower water temperature forces me to reduce the temperature change to 2 or 3F so that the temperature change times are reasonable. With a higher water temperature, I can comfortably have a higher temperature change (8F). What is more efficient?

Is there any other things I should try to find the most efficient yet comfortable settings?

Thanks.



When I had the

mark ransley

What do your pumps cost to run 24x7 with lower water temps.

BMac

The system uses the Grundfos UPS15-58 3-speed pump set to the lowest speed (I tried all 3 speeds with no difference in heat distribution - it just got louder). At the lowest speed it draws 60W which in my neck of the woods, costs around $2.80 per month.

Unknown

welcome to the trade off of outdoor reset.

Viessmann has built in setback buttons on some of their boilers/controls, is the vitola or the vitotronic one of them? If so, that might help. it would be something like a moon or a sun, probably.

John@Reliable_17

Just set it and forget it, that's whats nice about ODR. As far as savings, if you lower it, it has to reheat the building so if it's running you are not saving. When you are gone, no doors are opening, no vent fans on etc. so the heat loss is next to nothing, so you are saving. Just try to adjust so that on design degree days the unit is running all the time for max savings.

Darin Cook_9

Tstat Reset

High Mass hydronic systems with a programmable tstat should not be reset more than 2' or 3' at night. I really would not recommend resetting your tstat back at all at night . Whatever energy that you saved at night is lost the next morning when you try to bring all that iron and water back up to temperature. Let your boiler do all the resetting and call it good. This is why radiant zones typically have non-programmable Tstats and steel panel rads have set and forget heads.
Hope this helps,

Darin

BMac

I need a bit of clarification. I can control the temperature swings of the house by using the pump control thermostat (upstairs) with built-in timers, by using the Vitotronic control with it's built-in timers, or a combination of both.

Are you are recommending leaving the temperature constant within the house while sleeping/away/etc.? Or are you recommending using the Vitotronic control as the only control over the temperature swings?

Is it really more efficient to maintain a constant temperature within the house always, then to allow the temperature to drop during specific times? To me, it seems that allowing periods of lower temperature means the overall avg temperature of the house went down which equals less energy put into the burner.

Thanks again.

Unknown

but then you have to run higher temps.

If you can't target the "higher temps" to only run that way when you come out of reset, then you are always running higher temps, which loses efficiency as well.

the vitotronic should be able to do what you are trying to do, I think.

BMac

I took a look at my electrical bill and with taxes and a delivery charge, the real price of electricity here is around 12.4 cents/kWh. This comes to $5.37 a month for the pump. (I originally just went to my electricity providers webpage and found the price of electricity)

BMac

Sorry for my ignorance, but I am having trouble understanding the term "reset". The way I understand "outdoor reset" is the boiler adjusts the water temperature to the outside temperature in order to match the heat requirements of the house. I never did understand why it is called an outdoor RESET.

Unknown

If you target a fixed temp, it's a Set Point. Setpoint control.

If you keep changing the Set Point, it's Re-Set every time you change it.

I just made that up, but it's probably close

mark ransley

12.4c is a normal lower price so its not cheaper than Ng.I dont even bother with setbacks of more than 2-3f

BMac

Okay, so is the reset occuring because I am changing my target house temperature, or it is occuring because the temperature outside is fluctuating?

Unknown

outdoor reset changes water temperature based on outdoor temperature. You fiddling with the thermostat doesn't change your water temperature with your system.

however, the vitotronic might, if it knows you are going into and out of setback. I'm not sure though because I'm not up on my viessmann controls. I know some of their boilers will manage water temperature setback with no thermostats in the system though, so I imagine you can do this. You just would have to use your controller instead of your thermostat to do it.

D107

another way to say

what NRT Bob said: (HO here)
"If you can't target the "higher temps" to only run that way when you come out of reset, then you are always running higher temps, which loses efficiency as well."

is that unless your control allows a morning boost at let's say 180degrees water supply temp that temporarily overrides the outdoor reset, any setback more than 3 degrees in cold weather will take longer than you like to reach your set indoor temperature. And your curve/temps will be higher, which loses efficiency. For how many hours and with how much of a setback you need to see savings has been debated here often. 8 hours, 8 degrees you'd probably save something if you had a morning boost. Some people like to sleep in cooler temps than daytime. See if you can live with 3 degrees setback.

As for comfort, there's another factor to the setback. The time is takes for all your floors and furnishings, walls to come back to temp, which is longer than the air temperature takes that the room thermostat reacts to. We used to set the day temp back two degrees from 9am to 7pm, but now with no day setback it's much more comfortable. That morning boost though should be standard on all controls but it's not yet.

David

BMac

Thanks for your message - you are right, it seems obvious that the controllers allow a morning boost. However, since they do not it sounds as though the proper thing to do is either hold a constant temperature, or reduce the setback to 2 or 3 degrees.

I will use the upstairs thermostat (pump control) to bring the temperature down just before bed (I like a cooler house when sleeping) but just 2 or 3 degrees, plus as a high temperature cutoff when the house gets too warm. Other than that, the pump will run continuously.