Spoogster

What is a PReV outlet? We have an overflow / blow out pipe (sorry not sure exact term) already so I assume it would reuse that, but it just goes to the outside wall at first floor and not a drain

Hi all Our OVO heat trial design is dragging, due to the installer saying our airing cupboard 750mm x 770mm x 2.4m being too small to put a Daikin 250 l UVC, buffer, expansion and the OVO monitoring kit in. Question: is it possible to put the buffer and expansion vessel in the loft above the UVC?. Loads of space in there and I assume it would be possible to add insulation to those items in the loft. Are there building regs issues with this idea? Looks like others have done it. TIA Jason

I have found not all microbore is the same! We only have microbore drops from the ceiling down to each rad, from 15/22mm pipes, and 15mm upstairs to all rads. The positive with our house is that we are judged quite energy efficient (year 2000 build) with new triple glazing four weeks ago and a shed load of new insulation in the loft in January (cost about £140 from B&Q. The installers were happy that the system should work and have confirmed today that they will be installing a volumiser buffer. others on here are much more knowledgable than I so hopefully more input soon

Thanks Mr Tea. Yep I understand exactly what you are saying and ultimately I am going to impress on the installer to fit a buffer. just to clarify the weather here in Kent yesterday was dull and overcast for all but about an hour in total around 3pm where the sun was intermittent. Stiff breeze all day making it feel colder than it was. replacing the microbore would be difficult as it resides in the space between the concrete block wall and the dot and dab plaster board, so 15mm would be surface mounted and SWMBO would go nuts at that prospect! It would also mean lifting every floor upstairs and again modern construction methods mean large chip board floorboards - not easy. Definitely a buffer is the way to go. Will find out next week if the fitting company will play ball or just try to rip the arse out of the government funded scheme.

During this hopefully short cold snap I decided to do a little experiment to see how our existing gas boiler system works assuming it is set at 45c, to mimic a heat pump system. My main concern is obviously whether or not the microbore supplied downstairs radiators would work ok and heat the home. through today the outside temperature has been around 7 to 9 degrees. Our home is set at 19 degrees through the day. To date we have only run the gas boiler for an hour morning and four hours evening, again at 19c. For the experiment to mock up how the heat pump would be working through the day it has been running 0630 to 2100 hours. I have also purchased a temperature digital thermometer from Toolstation of the probe type (£10). This appears to be accurate against other thermometers I have in the home. I have managed to set the gas boiler to c45 degrees (quite a modern Worcester system boiler). First task was to see how the flow and return temperatures faired on the 22mm pipes direct from the rear of the boiler, for both the UVC recharge and rad heating cycles. interestingly the heating flow is 45.9c and return 40.0c, which is very close to that delta t which a heat pump would operate (5c I understand) and less than the 10c I understand most gas boilers work to. The UVC cycle was bout half a degree greater so that delta t is about 6.5c. the radiators in the ground floor which are fed by microbore seem to fair well. The single panel lock shielded rad in the hall was running at 44.5c so not much heat being lost en route to that one. The large two double rads in the living room at the opposite end of the house to the boiler were running at 42c or thereabouts, but these are the largest rads in the home. The living rads are well oversized though. so far the house has been very comfortable and the boiler has mostly been off. Taking off the hot water gas use I predict all day we have used 40kwh of gas, quite a chunk of which was in the morning getting the home from 16.5 to 19c (I would say 15-20kwh on that task alone). The real test will come on Monday and Tuesday when the temperature is going to drop to around 4-5 day but poss below zero evening. I would appreciate thoughts on our measured delta t of less than six degrees, as to my kind it would appear our system retrofit could hack running at 45c without problem high delta t. Ok the pump is set on it’s highest setting but noise from the boiler itself is the only thing we can hear. I am hoping our microbore is not going to be an issue, but if I am missing something please let me know. obviously the Monday and Tuesday temperature tests will confirm if 45c will heat the house so an update will be forthcoming!

Thanks Peter

that costing info is very useful. I am therefore going to push them very hard to add the buffer and pump in the cost and explain that Daikin strongly recommended. Daikin are a partner to the trial so I am going to push that too. there are too many people in this world trying to make a quick buck regardless of the consequences...

Just called the Daikin tech team who have been very helpful. looks like a buffer or low loss header is definitely the way forward. I am going to have to insist on one I think. The problem is that the installers on this OVO scheme appear to be budget capped so any increase in specification is coming off their margin, which isn’t ideal for them. I do know that at least one installer on the scheme has asked a customer to pay a £2k contribution as their install came to £15k. I’ve had £10.5k allowed so I’m unsure if a 7kw monoblock 410a and 250litre cylinder and install would leave any slack for a buffer and extra pump/circuit to be included. im torn here as I would like the trial to be a success and for heat pumps to be supported by the government going forward, but I get the horrible feeling installers are less concerned and could be throwing any old system in with little regard for outcome just to cash in (which in this case is like turkeys voting for Christmas). It is surely in everyone’s interest for the trial to go well....

I’m so out of my depth!!!!

Well, the best practice document was well worth reading. page 22: heat pumps not suitable for microbore because of lower flow rates. No in depth reasoning and quite a sweeping statement, and I have found a number of web articles where it has been used. Certainly one for questioning when the contracts manager comes to our house to discuss design. I suppose it is down to how much micro there is and where, fed by what other pipe sizes. Some of the guidance on buffer tanks is interesting and I don’t admit to fully understanding it, but there is the suggestion it can reduce efficiency through parasitic action. Hhmmm. Sizing is suggested at 10 litres per kW heat pump . Cycling should be less than 6 times per hour to stop parts wearing out. Begs some questions with my microbore issue: to stop cycling could it be advised that a number of radiators are lock shielded open so as to keep demand going all the time the main thermostat is calling for heat? Both our existing hall and landing are set up without TRVs for this reason I understand, but I cannot see why bathroom rads could not be also left fully open so as to act a bit like a constant calling loop to lower the potential for cycling (that would be total four or five rads depending on WC too)? Push and pull pumps on flow and return an option? Or, is there merit in running the HP temps just low enough to meet the heat demand of the home so as to ensure cycling doesn’t kick in too often, or does that cause issues with delta t? I assume low temp running would be more efficient but rad sizes would need to be further increased. I can see the balance or reasons why or why not being all over the place on this one. What I have taken away from reading the guidance is that good training on design is crucial and to put to one side your existing knowledge on gas heating systems - this stuff is much more complicated and no room for mistakes or slack/lazy design... if you hated maths at school you might struggle.

There appears to be a whole library of documents including best practice guide. I know what I am doing this evening!

Not just yet. The contracts manager is coming to our home in two weeks time to talk about position and pipes. I have highlighted that our existing airing cupboard is cramped at 700x800 and offered a handy corner of our breakfast room just below which would give 900x900. A slim type 250 litres Daikin cylinder is likely....

Peter that is a very stark warning if I have ever seen one! is it not then a case of adding a second pump and valve to isolate the buffer as you suggest, at either the heat pump or radiator side? Maybe I am being too simplistic. it would be helpful for me to understand why the HP life would be significantly shortened if no buffer is provided? Five year guarantee on the Daikin parts is being offered... fascinating and much appreciated.

I have also done a spreadsheet following your comment and using 0.515 against stelrad figures for each size confirms majority of existing rads should be fine at lower temps. Two rads will be lock shielded open (hall and landing) so I assume that will assist with short cycling? They aren’t massive but the hall one is being upgraded to K2 600x700. Not buffer tank size tho. has anyone though about my question of adding a buffer a year or so down the line?

Yes they have done room by room calls looking at existing K1 and K2 rads and appear to have reduced down to delta T based on 50c operating temp (which seems about 5c too high for efficient running). looking on the stelrad web site we look to have spare to cover 0.515