JohnMo

Update October final figure So gas consumption compared to 2021 2021 - October used 1,370 kWh for DHW and UFH or (assuming 5kWh DHW) 1,220 kWh for UFH only 2022 - October used 562 kWh or 412 kWh for UFH only Saving 59% Interesting the Jeremy heating spreadsheet, for November predicts 884kWh for heating only. So basically used half that, 2 people in house plus dog and solar gain all help. November Issues and changes made at the start of November Weather Comp switched off New UFH mixer, now have an IVAR mixer, with low temp thermostatic mixing valve. Much better control than the previous Reliance one. Heat meter installed upstream of UFH. Had the heating off for a couple of days at the start of November. When I restarted it the gas consumption started getting much higher than I was expecting. Had a fiddle with WC curves, but this made no real difference. WC was dumped in favour of charging the buffer to set temperature based on a thermostat and running the UFH in batch charging mode. UFH starts at 1 am and continues running until the room thermostat (in hall) gets to 18.5 degs, it then is switched of the UFH. Basically all UFH loops are open except bedrooms on a single zone, bedrooms are heated by opening the doors to the rest of the house. Still fine tuning, but flow temp set to 30, buffer (thermal store) I have set to 50 degrees, this ensures the odd opening of tap doesn't fire up the combi as the water leaves the thermal store DHW coil hot enough to by passed around the combi. November gas consumption compared to 2021 2021 - November used 1,754 kWh for DHW and UFH or (assuming 5kWh DHW) 1,604 kWh or UFH only 2022 - November used 1,138 kWh or 988 kWh for UFH only Saving 35.1% Interesting the Jeremy spreadsheet, for November predicts 1102kWh for heating only. This is showing less of a percentage difference than October. Explained by more heat being lost to the building fabric, possibly less solar gain, but still some. Average temp below zero for next week, so will see how this goes.

So your heat pump needs to be no bigger than 8kW, with a small buffer. 11 kW would be huge.

People love reinventing the wheel and spending loads to replace something tried tested and works. Smart thermostats and Trvs everywhere is great in theory, but be careful they don't increase oil consumption when the boiler starts short cycling, when it's only got one circuit to manage and has little or modulation.

Just looking at your heat loss calculation at 10kW. This looks very large for your u values. Our house has very similar u values, but is 193m2. But at -5 we have a heat load of 3.2kW. So yours should be in the ball park of around 6 to 7 ? My biggest issue is a gas boiler too big, at low flow temps it will do a min of 6.7kW, against a min demand of 0.5 (ave 10 deg day) and max 3.2kW. I have thick screed so chuck loads of heat at a time and use as a storage heater if I want. With the amount of water you have in the floor, operate as a single zone and you will not need a buffer. I would double check your heat demand, get as smaller gas boiler as possible. Going big is a needless expense and is a pain in a low energy demand house. You have about 1km more pipe in the floor as me as I am on 300mm centres and 7 loops and with a floor u value of 0.09, a flow temp of 30 degrees for 7 hours is enough to keep the house warm until the next day. Would expect a flow temp nearer 25 would be enough for you. Not sure who did your UFH design, they are quoting 113W/m2, and 40 degree flow temps, that's getting to be about 40kW going in to the floor, bit bonkers.

Your calculation for heat loss is now 5.2kW, considerable drop

Perspective 3 person household consumption of DHW is 5kWh Number of design days per year, very few. 31% of 5 x very few, is not much, full cost electric for an immersion.

Per reply in other thread. I think if you get your ventilation heat loss sorted the DHW will be fine. Also this is a calculation for your lowest day temperature. You have an immersion should it be required to heat water. With a heat pump making it large/oversized to suit the worst day of the year, makes it huge at all other times. On a 10 deg day when your heat load is less than 1kW, a huge heat pump has no chance of being efficient without a huge buffer.

Looking at the calc inputs for the rooms, your number of air changes per hours looks very high. 43% impact on heat loss. A property with 7 ach @ 50 pa and with wind loads applied would have an effective air change rate of 0.5. So 0.5 or better would be more appropriate. If you don't have MVHR the efficiency of that box needs to be set to zero. Correcting the above will half your ventilation heat loss.

Could you locate the plenums more centrally this would limit duct lengths. Reduce system pressure drop, less noise as the fan. Just buy the plenums there's normally enough other stuff going on and life's too short. I would use passivhaus flows as a good starting point up them slightly to get br rates if required.

@Jenki Did you end up buying one of these heat pumps?

To add to the above, if you have a prolonged cold period outside, such as central Europe experiences, and MVHR, then as you heat the incoming air with out going air, you can do reduce the relative humidity. A big house with only one person in it with sub zero temps for quite a few days could experience well below normal humidity levels. But not sure it's that likely in the UK. Our house today is sitting at 42% RH and 20 degrees inside, 6 degs outside and 77% RH outside.

You can specific airctete rawlplugs. A very course screw in type. I got mine from Screwfix. They fix stuff well. Screw in half a turn, the back a quarter turn, put them in slowly. Work a treat.

All I would say about Salus Auto balance actuators, is they keep a supply and return DT stable. They do not control or limit the flow temperature. So if you set your flow temp to 50, then return will be 7 degrees lower, at 43. If you set it 40, same again return will be 33. What they are designed to do, is keep the DT constant on each loop they are installed, irrespective of loops being switched on/off on the same manifold and a fixed pump speed.

You would have one nut either side of the white threaded part. Basically lock the first terminal, the other units, move the nuts out of the way, the inner one, screw well out of the way so it doesn't limit adjustment. When adjusted, pop the terminal out of the ceiling and lock the nuts.

I have mine on a internal wall on a double layer of 18mm ply from floor to ceiling. Little or no noise transfer. So you should be ok on a solid brick wall.

Have the cover in position, but wind out as much as possible while still having enough screw engagement to install the lock nut. Good luck

If it's where your are sleeping, generally poor ventilation could / would be the reason. So let's get a bit more info. Where in the room is the grille? What ventilation do you have, continuously running dMEV, intermittent bathroom fans or nothing? Do you have vents in the window, if so are these open or closed?

The more you split the system into zones the bigger the required buffer. If you had a big enough buffer then a couple of immersion heaters in the buffer would get rid of a need for seperate heater. Simplifying layout and piping runs. LLH have to be correctly hydraulically sized to work efficiently. So would steer away from them. Great for commercial applications. Many do not like thermal stores, but you can get them sized for heat pumps, the main difference is the DHW coil size, being huge (about 6.6m2). That way there is about 4 to 5 degrees difference in store and DHW temp. You keep the store at low 50s, supply heating and DHW. Here is a typical drawing showing the hydraulic layout of a system with an additional heat source as well as a heat pump. Pump for the gas boiler if not already within the boiler, follow boilers manual. Note: Hydronics just means a water based heating system. The hydraulics is the use and design of the system for water in the system.

All things are a compromise, which has the bigger hit on efficiency short cycling or heating a thermostat controlled buffer? The thermostat doesn't need setting very much above heating flow temp, hysteresis depends on volume I believe. The non thermostat buffer, doesn't require additional temperature to operate. So win win. That is how Kensa heat pump want the buffer installed. The difference in CoP for a 5 degree uplift in supply temp for a given outdoor temp 0.5. If you heat pump was sized quite closely to max heat demand, a clever option may be to bypass the buffer once it gets to about 4 or 5 degrees outside. Then short cycling should not be an issue anyway. You just need the defrost capacity is maintained in the system.

Any photos? What pump are you using? How many zones, does this occur in a steady state (ones all open) or when zones are opening closing etc What is the flow temp of the UFH and what is the supplied temperature from the boiler? Looking at the manual for a T4 mixer that should be 41 degrees

I started writing, but gave up it was too late and lost the will...

I have a couple of the central heating pumps, you just need to size them for your system. Also have a grundfos all are super quite. Is the noise the pump, or just the water moving through the system?

A buffer is just an extension of the heating system, it give the system more volume. The heat pump has to run longer to get it from temp A to temp B. Once the return temp of water to the heat pump is at a level to hot for the heat pump, it stops its heating cycle. The circulation pump continues running. When the return temp is within limits again the heat pump starts. There are two ways to manage a buffer. No thermostat Within the period of time from heat pump stop to heat pump start, the heating system draws heat from the buffer, the buffer temp rides up and down within a few degrees of it's set point, the same as the heating system. With thermostat Heat pump heats the buffer to a thermostat set point, this thermostat only managed the buffer temp, this is set hotter than heating system flow temp, works the same as a thermal store. Heating system sucks the heat from the buffer. Buffer is recharged by heat pump it doesn't know or care what the heating system is doing. A bigger buffer gives a longer the run time and longer the off time, less cycles more efficient heat pump operation. Heating system 0.1kW to max HP output, it doesn't care. The heating system is a seperate system, you could have a 10kW heat pump driving a 2kW heating system, with a correctly sized buffer. Down side is slightly high flow temp with the thermostat system, some vessels heat loss also.

25% higher that trickle.

A buffer will limit cycling, that's what they do. The bigger the buffer, the longer the run time and off time.