Heating Partial Load

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  • blowlamp
    Automated Home Sr Member
    • Apr 2017
    • 98

    #31
    Why don't you get some bigger radiators fitted? It sounds like it would help with the constant boiler cycling and give you a warmer home too.

    Comment

    • rs1987
      Automated Home Jr Member
      • Nov 2019
      • 44

      #32
      Originally posted by blowlamp View Post
      Why don't you get some bigger radiators fitted? It sounds like it would help with the constant boiler cycling and give you a warmer home too.
      I plan to try this, but my landlord is pretty unreasonable. When I moved in here there was absolutely no heating control at all. No timer on the boiler, no thermostat.

      I proposed to the landlord that I fit Evohome, entirely at my own expense, as well as replacing the existing Honeywell valve bodies with new Honeywell valve bodies. Zero outlay on his part.

      He refused.

      Only after I cited the 2015 building regulations that do not allow a landlord to unreasonably withhold consent for energy efficiency improvements if they're funded by the tenant did he finally agree, and grudgingly so.

      So I don't have an expectation that he will agree, even if I pay for these radiator upgrades myself (which I would do, since the cost of moving house is vastly more expensive with removal companies, end of tenancy cleaning, etc. etc, and anyway, I happen to really like this property except for the dismal heating performance).

      I am currently looking at some radiator upgrades, although in one case the available space does not allow for a large enough radiator (it's about 2000 BTU short of requirements) and another case the existing radiator is a very strange width of 950mm and I can't find any type 22s that are 950mm in width and higher than 600mm. The pipework won't allow a wider radiator.

      Comment

      • blowlamp
        Automated Home Sr Member
        • Apr 2017
        • 98

        #33
        Anything suitable here?

        Comment

        • mtmcgavock
          Automated Home Legend
          • Mar 2017
          • 507

          #34
          Originally posted by rs1987 View Post
          Yes, I turned Evohome back to its normal set point. It only anti-cycles, and infrequently, when the rest of the zones are up to temperature and there is only one rad open. It's a big improvement.

          You're correct that the rads are undersized in some rooms. So I have a double problem: oversize boiler and undersize rads. The main hallway rad is on pretty much permanently just to maintain the zone at 19 degrees. The living room rad is too small for the room but eventually manages to get the room to 21 degrees after a few hours, although it then is also on pretty much permanently in order to maintain the temperature. The conservatory (double glazed) which serves as a dining room has a woefully undersized radiator that cannot even maintain a 15 degree set-point in this weather, so I leave it off and heat with a 3kw electric radiator during the times I need to use the room.

          I'll experiment with different flow temps to check what the gas usage as. I really need to run at a higher temp to compensate for these undersized rads. I'm a little fearful of the result though, as I recall before I put in Evohome I had a gas bill of £200+ for 30 days usage in one month when running a flow temp of 65 degrees and only a few rooms in the house were actually being heated.
          Yeah with small/undersized rad sizes you need to be ideally running it at 75oc. You're possibly having the opposite effect running at lower temperatures - as the boiler not meeting/maintain set points it's just running constantly using more gas than it would at a higher flow temp. I'd run it at 75oc and see if it makes a difference - take meter readings and see.

          I wouldn't say the boiler is oversized massively when you think a normal system you'd have a demand of at least 50% in normal use which would equate to more than 5kw which it can modulate down to, i'd probably just the wrong boiler for the property. Sounds like it needed a system boiler and Unvented cylinder.

          Originally posted by rs1987 View Post
          So next step it seems is to have an engineer come and close down my bypass valve from the default to about 3/4 closed, if I recall your instructions correctly.
          If you've got bypass radiators such as towel rails etc. i'd be tempted to just close it completely.

          Comment

          • rs1987
            Automated Home Jr Member
            • Nov 2019
            • 44

            #35
            Originally posted by blowlamp View Post
            Anything suitable here?

            Hmm, you're right. I didn't think that this was perhaps an imperial size radiator I have in the hallway. All the others are metric. Looking at the sizes in this chart it appears to be a 37 inch. That said, the ones in this brochure are not tall enough to make any difference as my existing one is 600mm high and the highest on offer in this catalogue is 690mm. I really need something about 900mm high.

            I'll have to investigate whether a 900mm x 900mm or a 1000mm x 900mm could fit with a slight bend in the pipes on either size or perhaps a small shim for the 900mm wide radiator.

            Comment

            • rs1987
              Automated Home Jr Member
              • Nov 2019
              • 44

              #36
              Originally posted by mtmcgavock View Post
              If you've got bypass radiators such as towel rails etc. i'd be tempted to just close it completely.
              I do. Two towel radiators and one in the dressing room that I've opened to max to allow for some heat dumping to prevent anti-cycling.

              Surely closing these rads off would make the system go into anti-cycle mode more frequently?

              Comment

              • mtmcgavock
                Automated Home Legend
                • Mar 2017
                • 507

                #37
                No, I meant you can close the internal bypass completely. Think you misunderstood.

                Comment

                • rs1987
                  Automated Home Jr Member
                  • Nov 2019
                  • 44

                  #38
                  Originally posted by mtmcgavock View Post
                  No, I meant you can close the internal bypass completely. Think you misunderstood.
                  Ah right, gotcha - I did misunderstand. Thanks for the clarification.

                  Comment

                  • blowlamp
                    Automated Home Sr Member
                    • Apr 2017
                    • 98

                    #39
                    Originally posted by rs1987 View Post
                    Hmm, you're right. I didn't think that this was perhaps an imperial size radiator I have in the hallway. All the others are metric. Looking at the sizes in this chart it appears to be a 37 inch. That said, the ones in this brochure are not tall enough to make any difference as my existing one is 600mm high and the highest on offer in this catalogue is 690mm. I really need something about 900mm high.

                    I'll have to investigate whether a 900mm x 900mm or a 1000mm x 900mm could fit with a slight bend in the pipes on either size or perhaps a small shim for the 900mm wide radiator.

                    Yes, a 900mm wide radiator with a pair of these to get the right fit.

                    Comment

                    • bruce_miranda
                      Automated Home Legend
                      • Jul 2014
                      • 2307

                      #40
                      Originally posted by mtmcgavock View Post
                      No, I meant you can close the internal bypass completely. Think you misunderstood.
                      Just make sure you don't have a Zone Valve on the CH that shuts off before even the first radiator. That's when the bypass is really needed.

                      Comment

                      • mtmcgavock
                        Automated Home Legend
                        • Mar 2017
                        • 507

                        #41
                        Originally posted by bruce_miranda View Post
                        Just make sure you don't have a Zone Valve on the CH that shuts off before even the first radiator. That's when the bypass is really needed.
                        It's a combi, so there should be no motorised valves as the system isn't zoned as far as i'm aware.

                        Comment

                        • rarrarrar
                          Automated Home Jr Member
                          • Oct 2011
                          • 19

                          #42
                          I have a Vaillant ecotech 843 IQ with a EVohome system. The problem with the Partial Load D.000 set to auto is that when one or two rads call for heat it will often throttle the CH output so low that the CH water temp is only showing 40C for 30 mins or so - so no rapid heating of a room as required. I have set Partial Load to 24kW which stops this happening. D018 pump mode can also be set to Comfort which keeps the pump running all the time there is a heating demand. Finally I have reduced the anti-cycling time to allow the Evohome setting to dominate.
                          It does seem that all these eco controls are not suitable when the boiler is controlled by a simple on/off demand switch especially in old houses when individual rooms will have very different heating requirements

                          Comment

                          • bruce_miranda
                            Automated Home Legend
                            • Jul 2014
                            • 2307

                            #43
                            This is where OT should, in theory, really help. The ability to vary the Target flow temperature based on Heat Demand is what is needed.

                            Comment

                            • rs1987
                              Automated Home Jr Member
                              • Nov 2019
                              • 44

                              #44
                              Originally posted by rarrarrar View Post
                              I have a Vaillant ecotech 843 IQ with a EVohome system. The problem with the Partial Load D.000 set to auto is that when one or two rads call for heat it will often throttle the CH output so low that the CH water temp is only showing 40C for 30 mins or so - so no rapid heating of a room as required. I have set Partial Load to 24kW which stops this happening. D018 pump mode can also be set to Comfort which keeps the pump running all the time there is a heating demand. Finally I have reduced the anti-cycling time to allow the Evohome setting to dominate.
                              It does seem that all these eco controls are not suitable when the boiler is controlled by a simple on/off demand switch especially in old houses when individual rooms will have very different heating requirements
                              This is almost exactly what I have done. I've set heating partial load to a little more than the maximum of all my radiators open at once, D.018 to comfort, D.014 to 100% (thanks @mtmcgavock - this made a big difference, along with opening all the lock shields to full) and anti-cycle time to 15m, so at a 70 degree target flow the anti-cycle time is 2.5m.

                              What's your anti-cycle time set to?

                              Comment

                              • rarrarrar
                                Automated Home Jr Member
                                • Oct 2011
                                • 19

                                #45
                                Originally posted by rs1987 View Post
                                This is almost exactly what I have done. I've set heating partial load to a little more than the maximum of all my radiators open at once, D.018 to comfort, D.014 to 100% (thanks @mtmcgavock - this made a big difference, along with opening all the lock shields to full) and anti-cycle time to 15m, so at a 70 degree target flow the anti-cycle time is 2.5m.

                                What's your anti-cycle time set to?
                                Boiler max anti-cycle time D.002 is set to 6 mins ( default is 20)
                                EvoHome has min burn time of 3 mins and 6 cycles per hour.
                                Although short cycle times are in-efficient , in a large Victorian house with not great insulation and individual room controls waiting 20 mins before heat comes through is not acceptable.

                                It would be nice for Evohome to be able to adjust boiler CH temp based on zone demand %.

                                If I made the boiler choice again I would not have gone for the Green IQ model but one with less sophisticated control, however at the time it was suggested that new Regs could not be met with a more basic boiler and an on/off control from the EvoHome .

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