@ubert767 You have a UFH system and house size similar to mine except I have a Samsung Gen 4 Split 4kW. You were wise and chose a split system which is more efficient but, more importantly, has a PWM pump in the Hydrobox. This means that the HP turns down the flow automatically when it modulates the flow. According to the hydraulic performance (attached), it looks like it can handle up to 4.5m head at your maximum flow rate of 17 l/min for 6kW, so you have no problem as, if all are loops in parallel, loss can’t be more than 2m head, I believe. I have the same arrangement as you but have gone a bit further to take advantage of the PWM.
From the pump diagram, with HP only operation, it appears that the Daikin can modulate down to around 7 l/min or 2.5kW (dotted lines). If you only keep enough loops open to handle the minimum flow, you can apply zone/temperature control to the rest which will save much more if you have good thermal mass, solar gain and 1C hysteresis stats. The only issue though is the initial switch-on minimum flow required which could be 12 l/min in your case. This has to be investigated as each unit is different. My key room stats switch the HP on and off, including the open loops, which are secondary areas. With WC, I have long heating periods and long off periods with temperatures held within 1C. So you do not have to (naively, you say) follow the open loop charge. Horses for courses. This method is not possible with monobloc HP’s. Just some food for thought.
Thanks so much for your analysis of my set-up, from such minimal information from me too. My I ask from where did you find this technical information? I've found it very difficult to find any. I have a technical/medical background and found Daikin manuals to be almost beyond my understanding! So I just took a lucky punt.
No I don’t know what volume, I might look at the sheets again. Is it normal to have it recorded somewhere? It maybe somewhere as the system has had glycol or equivalent and anti leak a long time ago .
My explanation may be a bit unclear. My HP only turns off when all stats turn off, otherwise the flow modulates above minimum when stats turn on and off. You could of course leave the minimum flow on all the time and let the stats do their thing but this is sub-optimal in my opinion. The intermittency control factor saves energy.
There is one little quirk in all this discussion of open loops and that is the mandatory requirements of Part L.
Variable controlled room heating implies variable flows. If one has a fixed flow monobloc then what does this imply? Yea! A buffer tank, or am I wrong?
There is one little quirk in all this discussion of open loops and that is the mandatory requirements of Part L.
Variable controlled room heating implies variable flows. If one has a fixed flow monobloc then what does this imply? Yea! A buffer tank, or am I wrong?
Part L just requires thermostatic controls to "adapt" the heating output, so thermostatic on/off controls are sufficient. No need for variable flows or buffer tanks.
Of course on/off thermostatic controls aren't a good idea but can be "overcome" by setting UFH thermostats and TRVs to above the required temperatures thus effectively disabling them.
@RobS Don’t understand the logic here. If a thermostat shuts off a zone, its flow stops therefore the overall flow is reduced i.e. flow varies with stat controls. Therefore some interface is required to handle this variable flow as most heat pumps can’t. Of course, one can argue that the way to get around an inconvenient regulation is to ignore it by setting the stats higher and overheat, which will happen as exact WC matching is impossible. Precise heat control through intermittency and therefore energy saving is the intent of Part L here, even if this ignores the technical difficulty of achieving it efficiently.
This post was modified 2 weeks ago 2 times by Heatgeek
@RobS Don’t understand the logic here. If a thermostat shuts off a zone, its flow stops therefore the overall flow is reduced i.e. flow varies with stat controls. Therefore some interface is required to handle this variable flow as most heat pumps can’t
Why does it matter if the flow changes a bit, so long as its sufficient to carry the required energy? Mine certainly changes from time to time. No need for a buffer tank.
Variable controlled room heating implies variable flows. If one has a fixed flow monobloc then what does this imply? Yea! A buffer tank, or am I wrong?
I agree with the first point but not necessarily the second. Just let the flow vary (unless you have your system set up so that the variations can be extreme, which is contrary to good practice for running heat pumps efficiently.
Of course I also agree that variable controlled room heating is overkill in most circumstances and personally do not think BRs should require it. However doubtless Danfoss and Honeywell, who probably provide support to those who draft the regulations, would disagree.
Another argument worth applying is that this part of BRs is guidance. The actual requirement is only
It wouldn't be difficult to show that omitting the individual room controls meets the requirement in many/most cases with heat pumps, if you were so inclined. However since TRVs are nearly free, not many people would bother!
This post was modified 2 weeks ago 4 times by JamesPa
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
@RobS Don’t understand the logic here. If a thermostat shuts off a zone, its flow stops therefore the overall flow is reduced i.e. flow varies with stat controls. Therefore some interface is required to handle this variable flow as most heat pumps can’t.
The logic of Part L is a bit questionable in places! But why do you think most heat pumps can't handle this? Or more to the point, why most water pumps used in heat pump installations can't handle this? The same types of water pump in boiler installations have been doing so for many years.
Of course, one can argue that the way to get around an inconvenient regulation is to ignore it by setting the stats higher and overheat, which will happen as exact WC matching is impossible.
You don't need exact matching, just near enough that the occupants don't feel too hot or cold. The Vaillant style numbered curves and 4-point linear "curves" seem to work fine in the real world with continuous operation.
@jamespa@RobS. You are missing the point here. Part L states that EVERY room should have a thermostat to control the heat output. Practically then, if all stats switch off except one which has a flow of 1.5 l/min, how is a heat pump going to cope? It won’t and will give a flow alarm. Therefore, buffer tank? This question was posted facetiously to illustrate the poor quality of regulations which nobody takes a blind bit of notice of, as per the previous comments. There are many other smileys like “hot water cylinder should have ELECTRONIC control e.g. cylinder thermostat (sic)”. To boot, most EPC’s are not worth the paper they are written on as the evaluation process is poor. Maybe, instead of debating, some effort should be devoted to lobbying for better regulations that make sense.
You are all jumping to the defence of open loop systems. I was not criticising open loop. It is fine if you have a modern integrated PWM water pump with variable speed control; however there are people with monoblocs with fixed single speed pumps a la Ecodan. My own system is PWM open loop with some refinements. I was merely highlighting the irony in Part L.
@jamespa@RobS. You are missing the point here. Part L states that EVERY room should have a thermostat to control the heat output. Practically then, if all stats switch off except one which has a flow of 1.5 l/min, how is a heat pump going to cope? It won’t and will give a flow alarm. Therefore, buffer tank? This question was posted facetiously to illustrate the poor quality of regulations which nobody takes a blind bit of notice of, as per the previous comments.
I'm not and as I wrote the logic of Part L is a bit questionable in places. The regulations just say they must be fitted, not that they must be used.
Throwing a low flow error code isn't going to damage anything, might even act as a prompt for the home owner to find out more about how better to control their heating system.
You are all jumping to the defence of open loop systems. I was not criticising open loop. It is fine if you have a modern integrated PWM water pump with variable speed control; however there are people with monoblocs with fixed single speed pumps a la Ecodan. My own system is PWM open loop with some refinements. I was merely highlighting the irony in Part L.
Yet the best performing heat pumps typically don't use PWM pump control and are open loop...
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