jimseng

So the reason I asked this is to find out what the heat pump is actually controlling with a mixer valve if it is set to two zones. If it isn't an on off actuator with a switched 240v feed what is it? A humanoid robot that rotates a knob? A 0-10v analogue signal? Hence the term proportional. I get how a thermostatic valve could be set but @JohnMo mentions an electronic mixer. This suggests something more sophisticated than bypassing the manifold once a temp threshold has been reached.

My UFH pipework volume total for both floors (based on 12mm ID and total design length) is 105L. I have accepted that it is a good idea to install a 30L volumiser which, as I understand it, is for defrost cycles. So 130L total volume. This is well above the 64l based on 20l/KW So presumably this would be for the FF manifold as the requirement for the first floor (bedrooms) would be lower? Is the mixer a proportional valve or a simple on off? isn't the whole point to balance the system with the flow meters so the whole house is treated as one giant emitter?

Everything I have seen states that there is rarely a need for hydraulic separation. These comments confuse me! I will check regarding the TMV.

I am taking full ownership of the design of my heating system as there are too many parties involved with not enough skin in the game. I came to this in ignorance: Never built a house from scratch, never installed a heating system from scratch, never owned an ASHP before. Therefore I made the mistake of not understanding how important the calculations are for a well designed ASHP heating system are. The ignorance led to a lack of attention paid at the beginning but I am trying to catch up and at the very least get to a position on paper where I can see a calculated flow temp for my ASHP/house that will produce the heat output the maths says I need. This will be my starting point and from there I will be able to set the system up for best efficiency/comfort. On my side I have as much solar as I can fit on the roof and a decent amount of battery. I have good insulation, MVHR and I am trying my best to get the most efficient building I can afford. The heat loss calculations I have seem correct. I already have the GF UFH down and it is should output more than enough heat but until I see the actual figure I won't be satisfied, hence me banging on about it on here!

That's the problem, they have gone bust shortly after putting the GF pipework in. I know there are lots of factors such as floor covering, and given the current state of build and budget that might change. I was trying to get a rough guide. But those examples are certainly a good place to start.

Can I have the complicated answer? I have the heat loss calculations. I'm really interested in understanding as much of it as I can and this bit is where I need a nudge.

Hello all Following on from my other thread about buffer tanks and secondary pumps, I have now fully engaged with the design of my ASHP and UFH design. I am at the stage where the GF UFH is down and screeded. The UFH heating company (Mec-Serv) in Bristol has gone bust and so I can no longer ask questions. However really all I want to know is how to calculate the heat output from each loop for each room. Be gentle because maths makes my brain panic but I do have a functioning brain, it just takes me a little while. I would like to try and calculate this based on what I have, namely 16mm pipe at 150mm spacing with a given total length of loop. I guess we are going to have to assume the performance of the pipe, but how different can plastic pipe be? so presumably I have to come up with a w/m2, based on a flow rate and flow temp. I would like to plug this into a spread sheet so I can start to estimate a suitable flow temp for the given heat loss of the house. Just to note, rightly or wrongly I took the design of the UFH away from the ASHP supplier and I'm not desperate to change suppliers at this stage as I have already signed the contract and I think it would be simpler to go from here. Me, my builder and plumber and I are most likely going to do the FF UFH ourselves. I am trying to get my head around all the aspects of the maths so I know where I am. Like all things in life, it seems if I want it to be done right I have to do it myself.

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.