Originally posted by mtmcgavock
View Post
Vaillant flow temperature control for HW
Collapse
X
-
-
-
Originally posted by Symbolics View PostSorry, yes I did understand that using the NTC probe was one way to go. But I thought that the VR66 can alternatively take, as its input, the cylinder temperature dry contact that simply signals a demand for more hot water generation. This is the operating mode I am using. The primary benefit of this operating mode is that it allows me to site the Megaflo tank in the middle of the house, and the Vaillant boiler about 20 metres away in a boiler house. This keeps the noise levels down. Obviously the hot water has to travel over than 20 metres with very little heat loss - which it does, in my set up. I have Uponor district heating style insulated underground pipes and I lose less than one degree over that 20 metres.
Comment
-
-
Originally posted by mtmcgavock View PostEven when using the standard Stat on the VR66 the flow temperature will revert to the D.078 setting. The Hot water setting on the boiler stays active as it's a software limit, even when just using a Switch Live rather than a VR66 it's still adjustable.
It is also interesting that the boiler seems to look at the return temperature and set a flow temperature based on the incoming water temperature. If the return temperature is (say) 52 degrees, the flow will be about 60. Maybe this is to allow condensing to happen, but in this mode the boiler is modulating right down to 8kW. This causes a very slow heating of the cylinder, which in turn causes long run times for heating mode.
All in all, far from ideal, and I regret using the Vaillant boiler for this application. I may still buy a dedicated DHW boiler with a simple DHW temperature control that can just heat the water to the commanded temperature without too much additional undocumented “smart” behaviour getting in the way.
Comment
-
-
I don't know if this might help...
Vaillant ECOfit Pure 418, VR 65 Control Module & VR10 cylinder sensor, VRC 407F Controller + VR 21 Outdoor sensor + Radio Receiver in boiler + Sunvic SDM 1901 3-port
In a fully open vented system. With just basic clock, mechanical stats for controls, the boiler only allowed one temperature output of 60C (I think). I added the above Vaillant controls and can now set separate output temperatures for HW and CH, up to 80C. On CH the controls decide how hot the flow needs to be for CH, which usually means it stays below the maximum condensing operation temperature most of the time. It also now modulates it output much better than before, avoiding the on full/ completely off of the older system. Much less creaking of pipes as they expand and contract.Last edited by harrym1byt; 4 February 2019, 11:22 AM.
Comment
-
-
Originally posted by Symbolics View PostYes, I have D.078 set at 80 degrees. Regardless, what happens when there is heating demand is that the boiler goes to about 65 degrees on the flow temp, and then goes into pump overrun mode. So even when there is no NTC connected allowing the boiler to figure out what the cylinder temperature is, the output DHW is modulated down to 65, and the actual temperature varies between 60 and 65.
It is also interesting that the boiler seems to look at the return temperature and set a flow temperature based on the incoming water temperature. If the return temperature is (say) 52 degrees, the flow will be about 60. Maybe this is to allow condensing to happen, but in this mode the boiler is modulating right down to 8kW. This causes a very slow heating of the cylinder, which in turn causes long run times for heating mode.
All in all, far from ideal, and I regret using the Vaillant boiler for this application. I may still buy a dedicated DHW boiler with a simple DHW temperature control that can just heat the water to the commanded temperature without too much additional undocumented “smart” behaviour getting in the way.
Comment
-
-
Originally posted by Symbolics View PostYes, I have D.078 set at 80 degrees. Regardless, what happens when there is heating demand is that the boiler goes to about 65 degrees on the flow temp, and then goes into pump overrun mode. So even when there is no NTC connected allowing the boiler to figure out what the cylinder temperature is, the output DHW is modulated down to 65, and the actual temperature varies between 60 and 65.Last edited by harrym1byt; 4 February 2019, 08:57 PM.
Comment
-
-
Originally posted by mtmcgavock View PostTo me it sounds like you've got some form of circulation issue on the cylinder circuit, at a guess it sounds like it is returning too quickly or your pump is on it's way out. It's not a problem with the VR66 or the boiler setting at 65oc.
Comment
-
-
I was wondering if there was a further improvement that could be made to solving this problem.
I have a very similar situation. My Vaillant has Y-plan wiring (i.e. CH and HW heating fed with mid-position diverter valve) and I've implemented my own thermostat with software to control the room heating using TPI (with a relay to switch the CH demand signal). I am planning to move this to Opentherm to regulate the circulation temperature instead of TPI. However, when the hot water tank needs to be heated I would need to switch to a high enough circulation temperature.
This might conflict with the room heating requirement so I was wondering if I could have two modes:
a) HW demand OFF - CH is regulated using the boiler temperature OT control.
b) HW demand ON - set OT temperature to max and control CH circulation using the TPI signal (i.e. modulating the CH demand signal into the Y-plan wiring as before)
Would this work?
Comment
-
-
I don't have Evohome as I'm using my own control system. I was hoping that I could have CH heating at the same time as HW but not have the radiator feed running at full temp (which is currently 65C on my boiler setting). I was thinking that reverting to TPI would then avoid the rooms overheating. The diverter valve would be operating the TPI on/off switching in the same way as it does in my existing (non-OT) configuration.
Comment
-
-
I'm not sure if that would help me - but apologies if I've missed something. My boiler has only one circuit with one demand signal connected to it (terminal 4 on the circuit board) and is driving a single pump. There is a 3-position valve in the airing cupboard that can divert the feed to CH or to HW or to both. That is controlled simply by the demand signals from the two thermostats (CH and HW) i.e. the Y-plan wiring setup. I've intercepted those two signals and and am able to drive them directly.
Comment
-
-
Originally posted by Vikings View PostI was wondering if there was a further improvement that could be made to solving this problem.
I have a very similar situation. My Vaillant has Y-plan wiring (i.e. CH and HW heating fed with mid-position diverter valve) and I've implemented my own thermostat with software to control the room heating using TPI (with a relay to switch the CH demand signal). I am planning to move this to Opentherm to regulate the circulation temperature instead of TPI. However, when the hot water tank needs to be heated I would need to switch to a high enough circulation temperature.
This might conflict with the room heating requirement so I was wondering if I could have two modes:
a) HW demand OFF - CH is regulated using the boiler temperature OT control.
b) HW demand ON - set OT temperature to max and control CH circulation using the TPI signal (i.e. modulating the CH demand signal into the Y-plan wiring as before)
Would this work?
Comment
-
-
You've just given me an idea to try something else. My Vaillant 438 doesn't have a HW sensor input, but it can have a HW setpoint separate from CH. The HW set point dial is useless unless used in conjunction with a Vaillant wiring centre and Vaillant controls. I'm going to have a play with a Vaillant wiring centre and see if I can get the HW demand to register and make the HW dial operational. It will allow me to remove a lot of custom HA that I use to detect a HW heating cycle and then performing various actions, one of them being raising the max Flow temperature setpoint.
Comment
-
-
Originally posted by kevinsmart View PostYes, this should work and would at least limit CH overshoot on DHW heating
I'm assuming that the demand signal into the boiler will override what the OT control might be doing so - in HW mode - if HW thermostat has reached temperature and CH TPI control say OFF then switching off the demand signal to the boiler (terminal 4 on my Vaillant board) will stop the circulation.
Comment
-
Comment