ODR question(s)

Roland_4

I will soon be installing a Tekmar 256 ODR control on my Burnham PVG-4 boiler. I have read and understood the instructions for this unit. I know which numbers to punch in for my heating system. I am using a LUX 500 thermostat progammed to provide 70* when house is occupied and 62* when un-occupied and at night. Should I be using less (higher temps) set back? Some on this board feel that the boiler will have to work harder to bring the house up to temp thereby negating any savings from the lower night/unoc temp. The big question is: just how exactly is the 256 controlling the operation of the boiler as outdoor temperature varies? Will there be any conflict with the set-back theremostat? Also, how does the operation of the 256 interact with an indirect DHW demand. Thanks,Roland

Mitch_4

I attended a

honeywell course once and the instructor said no more than 5° for setback.

Do not know if that still holds true

Brad White_184

So many variables...

I can imagine a well-insulated, high-mass house (exterior insulation on masonry for example) holding heat very well. You could drop the bottom out of the thermostat and the building would not lose temperature very quickly and not go so low such that a fast AM pickup can happen. All that while you are not burning fuel which is the idea....

Take that same house, uninsulated masonry and the heat may hold a bit, but once the mass is cooled, your time to warm back up might be better measured with a calendar than a clock.

Imagine a low-mass and somewhat leaky house with abundant radiation and boiler to support it- a fast warm-up but also a fast cool-down. Same house with a marginal or precisely sized system? Fast cool-down and long warm-up.

Personally, I use data loggers and track the cool-down and warm-up slopes. If the cool-down slope is rapid, I have sealing to do (or recommend). If the warm-up slope is long and flat, I may have some radiation to add in addition to tightening up the envelope. I can color in the "overlap" between the down-slope and the up-slope to show my savings graphically. Not in dollars or therms directly, but as an order of magnitude to my heating on-time.

No real answers here- each house and climate is different. One bit of advice I read here on the Wall was to see how far your house temperature dropped in two hours after shut-down. Let that temperature be the night setback temperature.

Is that the best way? Maybe- it was as good advice as any.

David Laidlaw

many set-back rules are reasonable

What saves money is the time that the building is at a lower temp. The heat loss (and hence the cost to replace that heat) is proportional to the difference between inside and outside temperature. The cool-down and heat-up times roughly balance each other out, so that time doesn't count as savings.

The 2-hour rule is reasonable because that lower temperature will be maintained for several hours. Also, most heating systems are sufficiently sized that they are likely to recover that 2 hours of loss in less than 2 hours.

The 5 degree rule is reasonable because 5 degrees typically generates small but noticeable savings, typically isn't too uncomfortabl, and is reasonably quickly recovered in the morning.

Hope this helps!

Gerry May_2

Can't use a 256 control with indirect DHW unless you have a different control providing DHW priority......You should get a 260 which has the DHW priority along with some other neat features.
PS
I think....(My opinion)... is that the setback temperature depends upon the building characteristics and your lifestyle. If you can sleep in cool temperatures...The more energy svings for you. If You are out all day at work, why heat your home when nobody's there? the amount of enrgy required to heat the home depends on (among other things)delta T, so colder the room temperature, the longer the period of time that it will take to get the room up to occupied temperature from the unoccupied schedule period...... Make sense? I don't know. I would say that Honeywell likely studied the subject...in depth.. So 5 degrees F seems OK

Roland_4

ODR Question(s)

Thankyou all who responded to my inquiry. The set-back temperature information is much apreciated. The Tekmar 256 is going to be used in conjunction with an ARGO ARM-2P boiler control which has a DHW priority feature. The 260 is a nice unit with more capabilty but it's way more expensive and more than I need for simple ODR function.
Thanks again,Roland

Roland_4

ODR Question(s)

Hi Brad, for my amusement,I bought a LASCAR EL-USB-2 temperature/humidity datalogger. Thanks for the tip on interpreting the slopes of the temperature data. Would it be possible for you to post some data in graphical form with your interpretation of the results? Thanks,Roland