Few questions about heating curves and room sensor

Kopec

Hello,



I have at home the Buderus Logamatic 2107 Control and I would like to ask some questions concerning the heating curve. Hope someone has got the answers for at least some of those.



Let's now have a system without a room sensor. I do understand, that it takes outside temperature as a variable and computes water temperature according to the heating curve. The water is then sent to the circuit and the thermoregulator valves care about the room temperature. Now it's time for question one:



1) Why do I set a desired room temperature on the Logamatic 2107 if it merely controls the water temperature and the room temperature is done by the TRVs?



Now lets say I have a room temperature sensor connected. In the (both service and user) manuals they claim that the temperature difference between the actual temperature and the desired temperature influences the heating curve computation.



2) How exactly?

3) Does it stop/slow down heating if the desired temperature is achieved?

4) Therefore if I set 21°C, does it mean there is going to be 21 in the room?



You can also set a limit this room temperature influence in degrees. I understand that more degrees (up to 10) the more influence and vice versa, but



5) How exactly is the limit used?

6) Is it a limit on the room temperature or water temperature.



Now something little bit different.



7) The FreezTemp setting is used for the boiler not to freeze or not?

8) If yes, why is it set defaultly to +5°C outside temperature and not less and water temperature.



Thats all. I would be very grateful if someone could answer at least some of my questions.



Thanks, Martin

Gordan

I'll try

1) You don't put a TRV or other control device on the "zone" that's monitored by indoor feedback. There should be some guidelines about selecting the zone that indoor feedback will monitor; since it's changing the system temperature and therefore affecting all zones, and the TRVs on the other zones can't increase heat to their zones but can only limit it, you generally select your "worst case", most demanding zone for indoor feedback, and TRV the rest.

2) I don't know the "secret sauce" for the 2107, but typically there's a PID algorithm that boosts supply water temp in proportion to how much under the setpoint the measured indoor temperature is, and how fast it is approaching that setpoint. So 3) it would reduce boost before the setpoint is reached in order to avoid overshoots, and ensure that the 4) setpoint is reached and maintained.



6) The limit is on supply water temperature. 5) Ideally, this would be set wide enough to give indoor feedback enough authority over supply temp that it can adequately maintain the temperature in that zone when things are "ok", but not so much that an emitter malfunction, an open window, some sort of heat source (or a crowd of people), or other such anomalies could put the supply temperature out of whack for all the other zones.



7) Yes. 8) +5 C as a safety margin, and air temp (and not water temp) because it can't adequately assess water temperature in the system unless it's circulating, which it won't be unless there's a call for heat (freeze protection moot) or the freeze protection is on. Chicken and egg, sort of.

Kopec

Thanks + 2 more questions

Thank you very much for the replies, they are very helpful. I hope you don't mind me asking some more details of some of the answers:



1) Do I understand it correctly, that if you wouldn't have a room with temperature feedback (no room sensor in the house), then setting the room temperature makes no sense as it would just boost/lower the water temperature, but not maintain any specific room temperature?



8) So if my boiler is situated well inside a house and all of the plumbing is done so that it won't freeze up until like -10°C or probably even less, it makes perfect sense to set it to a lower value? I am asking, because I don't think I want the boiler to circulate the water continuously (as written in the service manual) when outside temperature drops below FreezeTemp, because the temperature inside the house is +17 degrees at minimum and so the plumbings and boiler areperfectly safe of getting frozen.



Martin

Gordan

More answers

If there's no indoor temp sensor, there's no indoor feedback. It still, however, makes sense to set that parameter because it has an influence on the OUTDOOR reset curve. Heat loss is (roughly) proportional to the difference between indoor and outdoor temperature. The controller computes the correct heating curve slope and offset from the parameters you supply, including the desired indoor temperature. Otherwise, you'd have to reprogram the outdoor reset curve every time you want to change your indoor temperature.



As for freeze protection, I'm not sure about the 2107 specifically but generally this runs when the space heating mode is disabled. So, someone is specifically NOT heating the house, but freeze protection acts as a safeguard to prevent damage to plumbing (not just heating system, but in general.) The controller manual should have more specifics.