jimseng

Indeed. This is becoming an academic exercise but I am interested in getting some calculations as a base line. Everybody here has really helped me get a better idea of what's involved.

I'm guessing this is because the UFH and ASHP might be installed before we finish putting the windows in or the roof on? The architect is pretty much dismissed at this point, apart from the odd chat and question about minor details. This is what I had in the initial estimate. But, under advice from my plumber I decided to go with another UFH supplier and this is probably my first mistake. Having never built a house before or had an ASHP before I was ignorant of the calculations necessary or how necessary and involved the design process is. That is why I am here getting help trying to figure it out. I should have paid more attention at the beginning! I am thinking that these heat loss calculations probably aren't way off the mark. However, it is obviously a different UFH system that has been installed. I suppose if I can work out the heat output for each UFH loop in a room at a given flow temperature, taking these heat loss figure for now that would help me pin down a target flow temp for the ASHP. Is that a reasonable approach?

I think the point he was making was that with solar gain, being able to shut off a zone will reduce the amount of heat required and therefore reduce the amount of energy consumed. Or something. I'm not sure what you mean by this? I gave them the plans and they returned a quotation which included an emitter schedule with the heat loss for each room. I added up the totals and that is where I got the 3.3kw heat loss for the building. Although my heat loss figures come out higher based on your spread sheet. The architect is coming back to me with their figures. The installer is MCS accredited.

Yes. It is going to cost me 6.5k materials and 3.5k install and commissioning minus the 7.5k BUS. Although I haven't had the cost of the secondary pumps taken off yet. And I opted for a 300l UVC. They are funding the BUS. This was significantly cheaper than another quote I had for a Stiebel ASHP. The plumber said he could do it cheaper but it required a big bill for the MCS inspection and sign off, and I would have had to fund the whole thing up front so I went with the simpler option.

So I did have a fairly robust conversation with the ASHP supplier. I have opted to have no zoning and insisted on there being no buffer or secondary pumps. They are now installing a 30L volumiser (which is in fact a buffer tank but with only two ports connected apparently). He maintains that by not at least zoning each floor I might get an increased COP but it will cost more in the long run. I maintained that adding actuators to the manifold at a later date is something I can easily do if I need to, but I would prefer to monitor each room temperature, gather data and balance the system with the flow meters over time as I learn how everything performs. As for the heat loss calculations, which are all based on drawings because the house is still in build the ASHP company said: "Our heat losses are based on MIS 3005-D we have to use this standard when sizing and designing a heat pump." His view was that recently (in the last 3 months) the ventilation heat loss calculations have changed and been downgraded as they were considered too high. Certainly, for my living room they comprise nearly 50% of the heat loss calculation. It is all bewildering to me. I concur, but what do I know. I have never owned a heat pump, an efficient house or lived with low temperature heating before.

If we are talking about between GF and FF then just a layer of Rockwool. The roof space is 350mm warmcell insualtion as it is considered a warm room. I'll see if I can find a u value for the floor. The heat loss from your spreadsheet is coming out at about 80% more than what I had back from the original UFH emitter schedule for the one room I have started with. I'm trying to find out why.

Thanks for this. Not quite sure what to put in place for ceiling, floor or ventilation loss. The floor is UFH sat on top of a layer 150mm of celotex insulation, then screed. For the room I am calculating it is a living room with a heated room above. Can you check my inputs and correct accordingly. If I can get this one right I can go through the rest of the rooms. I really appreciate your efforts.HeatLoss1.ods

Thanks @SimonD Yes indeed. OK so I have been relying on figures from the heat pump quote. Perhaps you could indulge me so I can go through and try and calculate each room myself to check the figures. Following Heat Geek's guide I have done a calculation for my living room. I have probably got this wrong so forgive my ignorance. Also, since the house is still under construction I have to go with the architects wall build up U values, proposed window U values and hope the builder achieves the figures. "External wall to achieve: 0.13 W/m²K" "Windows to achieve: 1.4W/m²k" I don't know how we consider the internal walls, or the fact I have an MVHR but perhaps we could start slowly so my head doesn't melt. 2 external walls with 2 windows, DT of 24 deg: Walls 22.7 m2 (22.7*0.13*24) = 70.83w Windows 6.05 m2 = (6.05*0.13*24) = 203.3w Total 274w for the two external walls. Where do I go from here?

Just to resurrect this thread. I am going to pay more attention before I go any further with the install. I am going to go back to the suppliers for more information but to get me started, I need to make sure I understand what I have to establish. To take the figures from the UFH supplier: If I add the output column for this floor I get a total of 4026. Is this 4kw of heat output? With similar for the second floor that is close to 8kw. A house with a supposed heat loss of 3.2kw this seems too much. But I presume this is with a flow temp of 45 deg (45/40, is this flow temp and DT?) I guess I am going to have to calculate the output with a flow temp that matches my heat loss? This would presumably determine the flow temp of the heat pump and therefore the required size of the heat pump. Am I on the right track or wildly mis-understanding things. Let's start with this given that everybody is so helpful. I need to look closer at how the heat loss was established, the SAPS printout doesn't help me because it is hard to decipher but I am working on a 3.2kw heat loss for the house at the moment which I guess is about right.

That is a good point, but perhaps it is due to the pipework layout as the majority of the feeds pass through the hallway? The 35c flow temperature was based on what I told them many months ago, but if I set a lower flow temp that is a good thing is it not? But perhaps the implication is a smaller heat pump. 5kw is what was specified by the SAPS calculations with a flow temp of 55. I specified 35 after conversations with various heat pump suppliers. The quotation for the installation came in at about £2000 including commissioning after taking out the BUS grant. I have signed the contract so I am where I am, although the ASHP supplier is very approachable and only the GF UHF is fixed now. I don't have to run the UHF at 35, I can set any level and I intend to collect lots of data and learn how to get the most out all my energy demands and sources.

Yes, based on my guesses of how the house would end up. Although I don't have the budget for floor coverings. If I can get to a plaster finish that would be a big achievement with the money I have left at the moment. Can you be a little bit more specific? I'm going to go back to them in the new year and get more details of what they are planning, now I know a little bit more. The installer originally quoted for doing the UFH install too but it was my decision to go with someone else. I don't know if that was a mistake but it seemed the cheaper route at the time. The ground floor has been screeded and will probably be a tile finish. The first floor UFH is routed boards with probably a wood and rug finish, although it might end up mostly carpet a few years down the line.

Low and slow for me. Minimum amount of electricity consumed for maximum comfort. What comfort actually means will only be established once I move in but "efficient" for me is highest cop.

The threat keeps them quiet. I expect the older one is a bit chewy.

Assuming the heat loss column is in watts then 3320. I think that tallies with the SAPS data, although that is reams of info and hard to decipher. I'm very grateful for you taking the time to explain this. I have not managed to find anything detailed for this unit yet, just a single page data sheet, but I am looking, in between the cooking my nieces and nephew expect of me. And if the regurgitated potato the dog left for us on the floor this morning is anything to go by she needs to go to the beach. (She has since re-eaten the potato).

Yes. Just the ground floor so far with a manifold and nothing else. Can you explain what that means? I am finding that I have to double check everything the "qualified" professionals tell me because it seems no one cares nowadays. I'm happy to do this myself if I have the means, I really want to get this right before it goes in. These images may be of interest, maybe not.

This is probably my fault but after going through various options I elected to have the UFH designed and installed by a different company to the ASHP supplier. But this is where I am, it's too late to change that now. But I can get the ASHP design right with the right knowlege. This is the bit that concerns me. The worst thing I find is those who say "That's the way we always do it". So to summarize: I am gleaning from this thread that, given that I want to achieve the most efficient system, I don't need or shouldn't have a buffer or secondary pumps? To me this leaves the flow rate up to the heat pump control system which, from the little I know as of now seems like the best option. I'm going to go back to the installer in the new year and query this and, to be fair, they are responsive, if a little dismissive of my technical questions. I need to be in a reasonable position to argue the case if I am to change the system design. As for the DWH cylinder. I chose a large one and have not had any push-back on it being over-sized for a 3 bedroom house. Yes it is big but to me, and my need for deep, long baths I would be furious if I installed one too small. I would never get over it.

It is a 5kw heat pump. PWM flow control. According to the UFH designs the pipework length is 920m for the whole house. With 16mm pipe / 12mm ID I make that 104L. The spec for the heat pump states a flow temp of 15 - 75 deg. Is it possible the "buffer tank" is in fact an expansion vessel, or does the fact there are secondary pumps in the quote mean it is in fact a buffer tank? I'm going to go back to the installer and get more information, this is all useful to me. So the main point of the question is do I need a buffer? The answer seems to be no. The second is do I need secondary pumps if I don't have a buffer. Are they specified because of the buffer? The UFH on the ground floor is already installed and the screed is down. (150mm insulation, 75mm screed) The FF heating is 22m routed boards and 16mm pipes, that won't be going in for some months. The DHW is possibly for a different conversation although FYI I have opted for a 300l cylinder, despite me being a single person with no kids. It is a house suitable for a family. Yes solar, yes immersion strategy.

Hello. I don't know what more information is needed to guide me on this but I have been trying to learn about my installation before it takes place and after having watched quite a lot on line (dangerous for someone ignorant as I am) I am wondering if I really need a buffer tank and secondary pumps. I am half way through a new build of a 158 sqM house which is designed to be very efficient (MVHR and masses of Warmcell insulation) I have been quoted for a Samsung Gen 7 R290 ASHP, the data sheet says a min flow rate of 7 L/m and max flow rate of 48 L/m and the design flow temp for my system is 35 deg. There is UFH on both floors with a design flow rate of 7.3 L/s (gf) and 12.1 L/s (ff) and I am not planning on doing any zoning. The ASHP quote specifies a 30L buffer and secondary pumps so I am assuming that is one pump per manifold. I have seen it stated that buffer tanks are not always necessary and I am wondering why this is, why I have been quoted for one and whether I am fussing about nothing. I'm not looking to shave extra pennies off the installation but I am obsessing over getting the most efficiency out of my system and I am averse to "that's the way way always do it" approach. There is a possibility that the 30l tank is an expansion vessel and not a buffer tank. If so that would leave the question why do I need secondary pumps. If it is a buffer tank then I am wondering if I should consider secondary pumps with controllable flow rates rather than set and forget. Happy Christmas by the way.

I don't think it is really about having a disconnection point in the loft. I started this thread wondering if there was any point in having the SPD/Fuse/MCB box in my first post. I have concluded that it isn't as @Dillsue pointed out, what is the point of a fuse given the short circuit current of the panels? So I think I will stick with MC4s and buy a cheap crimper for the 8 terminations or so I will have to do. This seems the safest way to make the connections over any period of time, day or night when I come to it.

Thanks. Lower risk is the important phrase there!

I'm actually thinking of buying a pair of MC4 cables and cutting them in half. This would give me 4 MC4 connectors outside the roof to connect to the ends of the two strings and I would bring the cut ends through a cable entry and through the internal membrane inside the loft. (I don't have roof felt, it is OSB and a breathable membrane under the panels.) So really I either choose MC4 connections and buy a crimper or terminate them in something like an Isolator or a termination box, whatever the term for that is. Personally I think the isolator fire risk is slightly overblown, especially as I will be able to easily inspect it. It's not like it is tucked away in a crawl space. I'm going to have to make a decision.

@Dillsue Really the only reason I am thinking of putting any termination in the loft is to avoid MC4 connections in the run from the last panels to the inverter. It is not a living space from the building inspector's perspective but I will be using it for some purpose other than spider accommodation and it will have a fixed stair case. (a 10m Scalextric track and guitars perhaps?) An isolator seems like a neat way of terminating the feed through the roof to the cable run to the ground floor. I guess that means it is quickly and easily accessible (and therefore inspectable on a regular basis).

The thing that confuses me over the SWA discussion is that I plan to use PV ultra cable, which now comes in an SWA version. I was planning on running it from the loft to the ground floor and to the inverter inside the service voids/posi joists using safe zones. This is only a 3m drop. This is from Doncaster Cables: This strongly suggests I don't need to use SWA which adds about £3.00/ metre. I'll use SWA if I have to but unless "without the need for conduit installations" means "must be run in conduit" then I'll go for the cheaper option.

@ProDave Can you remember if this has to be fitted to the flue pipe first (I suspect it needs tightening but I can't tell from the image) or can the flue pipe be inserted through it once it is in place in the wall. It makes a difference to me in planing the date for the insulation. Thanks

I think I have found it: