Logamatic--fine tuning heat curve

J. Cricket

A couple of degrees offset shouldn't make any difference, but certainly, with much hotter water you'll get the famous bang-bang effect where you will feel warmer when the heat is on but then it will go off for longer periods.

Also, if you are sensitive to 1F temp changes, your sensor may not show those changes. I don't know your system, but I know that Honeywell thermostats are programmed to pretend that they are holding the set temperatures (say 72) when the actual temperature is anywhere between 70 and 74. (This is dishonest but keeps customers happy.)

Dan_15

Due to the fluctuating warm/cold weather in Boston the past few days, I have had a good opportunity to see how well my constant circulation system works in different conditions. I think I am getting the hang of understanding the heating curve but I still have some questions as I try to fine tune the system.

When it got warm outside for a few days, I observed that the rooms were not heating as well in warmer weather. I have fin-tube convectors in all the rooms, which are probably similar to high temp baseboard. With convectors, Buderus advised me to keep the ref temp at the factory setting 167* and set the room comp to 18 for maximum indoor reset control. So, instead of changing the slope of the curve I decided to try experimenting with a a couple degrees of positive offset. Then it got bitter cold again. I keep the room sensor set to 72* because I have no insulation in the walls and that seems to be the optimal comfort setting. The wierd thing that happened with offset is that the rooms now feel too hot at the same setting of 72*. I had to turn it down one degree to 71* in order to maintain comfort.

Am I thinking about this wrong, or is it possible in a constant circulation environment for the room to "feel hotter" at a lower temp, when the emitters are running hotter? And how does this affect efficiency? Am I barking up the wrong tree with offset? Should I really be focusing on changing the slope of the heating curve by adjusting the ref temp?

It feels like I am fine tuning forever, but on the other hand I do love learning about how it works.

Thanks!

Mike T., Swampeast MO

is it possible in a constant circulation environment for the room to "feel hotter" at a lower temp, when the emitters are running hotter?

I believe so. I've experienced the same effect as well as the opposite--room "feels cooler" at a higher temp when the emitters are running cooler.

[Usually] if the space is comfortable at warmer outdoor temps and gets too cool at colder outdoor temps you want to increase the slope as opposed to the offset. Increasing the offset increases the supply temp at ALL outdoor temps--not just more as the weather cools.

As to the effect on efficiency? That gets crazy! If you have a condensing boiler its' efficiency increases as the supply temperature drops--but if you have to maintain a higher room temperature to maintain the same comfort level??? On the other hand if you reduce boiler efficiency by maintaining a higher supply temp but a lower room temp??? I won't swear at this, but for the same comfort I believe it's slightly more efficient to have warmer emitters with a lowered room temp.

Dave_4

Dan you should have a zero offset and if you want to play with your system try lowering your ref temp i am on baseboards and got mine to 142 works on warm and cold day today it's 20F and I'm heating no problem at 73 with 138F water. I'm using the 2107 with bfu room sensor

thanks
Jason

Dan_15

> _I_is it possible in a constant circulation

> environment for the room to "feel hotter" at a

> lower temp, when the emitters are running

> hotter?_/I_

>

> I believe so. I've experienced

> the same effect as well as the opposite--room

> "feels cooler" at a higher temp when the emitters

> are running cooler.

>

> [Usually] if the space is

> comfortable at warmer outdoor temps and gets too

> cool at colder outdoor temps you want to increase

> the slope as opposed to the offset. Increasing

> the offset increases the supply temp at ALL

> outdoor temps--not just more as the weather

> cools.

>

> As to the effect on efficiency? That

> gets crazy! If you have a condensing boiler its'

> efficiency increases as the supply temperature

> drops--but if you have to maintain a higher room

> temperature to maintain the same comfort level???

> On the other hand if you reduce boiler efficiency

> by maintaining a higher supply temp but a lower

> room temp??? I won't swear at this, but _B_for

> the same comfort_/B_ I believe it's slightly more

> efficient to have warmer emitters with a lowered

> room temp.



I won't swear at this, but for the same comfort I believe it's slightly more efficient to have warmer emitters with a lowered room temp.

Dan_15

"I won't swear at this, but for the same comfort I believe it's slightly more efficient to have warmer emitters with a lowered room temp."

Mike, that's very interesting--I am going to try and test that theory by monitoring the burn time and frequency for hotter emitters and lower room temp, and comparing that to known burn time/frequency for cooler emitters and higher room temp. So far it does not seem too different. At 22* outside now, I am burning for 5 minutes, with 12 minute intervals between the end of a burn and the start of the next.

I always thought that in a constant circ environment, modulating the emitters to be as cool as possible would result in the best efficiency. But I am intrigued by the relationship between room temp and emitter temp. I suspect that the Buderus indoor reset sensor helps squeeze as much efficiency as possible out of warmer emitters in order to maintain lower room temp.

Do you think that a high mass system would change your view of efficiency? Mine is converted gravity with a ton a water moving through 2-1/4" mains. Are hotter (and therefore longer) burns more efficient for a high mass system?

Thanks!

Mike T., Swampeast MO

Rather doubt you'll be able to get meaningful data to disprove or prove--SO much is subjective and it takes a long time for constantly driven systems to stabilize.

I DID qualify that statement with for the same comfort. If lowered consumption is the goal than minimum supply temp and space temp can give extraordinary results (provided the boiler is designed to efficiently deliver low temps).

I suspect that the Buderus indoor reset sensor helps squeeze as much efficiency as possible out of warmer emitters in order to maintain lower room temp.

Again, I suspect you're correct--if you're not than you should be...