Shaun McD

Sorry, my bad! I just assumed the zero VAT rate still applied without confirming!! Since it no longer exists then naturally this thread is out of date and can be ignored! Thanks for taking the time to respond @Conor

Hi all, We are started our self build just over the border from Northern Ireland, and we have a VAT rate of 13.5% on all construction materials here. During our last self build 8-9 years ago, we found a few suppliers in Northern Ireland who sold us materials at 0% VAT, provided we collect ourselves. Does anyone know what sort of tracking is done on new builds in Northern Ireland for this? For example, if I can get the address of a new build in Northern Ireland and say buy a heat pump, have my address as the new build in Northern Ireland on the account, but collect myself, is there any chance that the new build would get audited and someone flag that two houses worth of materials have been purchased against it?

This is very similar to what we have chosen, we are using a breathable racking board, we have opted for a 70mm internal insulation board, and in place of the VCL, we are taping the joints. Another detail we have is to return a 25mm insulation board on window jambs to kill the cold bridge from window to frame. We have a calculated wall uvalue of 0.13. Our frame is 400c so hoping that will help with wall firmess, but may still look to use OSB behind kitchen, and otherwise use 15mm or 2 x 12.5mm for utility/plant room.

I think with the doors opening in we will be looking to place mats on the outside of the doors (both have covered porches) I looked at their site and all the glue down options stated as 2, 2.5, or 3mm, do you know that to be incorrect?

Hi all, Finalising details for our insulated slab and need to lock in door threshold heights! As confident as one can be with an impulsive other half, we plan to use Karndean (or similar) glued down for the 3 areas with external doors, two open in and one slider. We have not yet picked the specific style of floor and when I spoke to retailer, they recommended leaving 7-9mm for a flush threshold height (3mm leveling, 2mm glue, 2/3mm floor covering). Can anyone confirm those sound right before we lock in heights? I am leaning closer to the 9mm side and can also compound floor up a little at doors it needed, Kind regards, Shaun

Hey John, I am by no means an expert in this field, I did the design and installation in current house and planning the same for the next one. Couple of small points maybe worth considering; Loft location is convenient in one way, but is also a torture in another. You need to access the machine to change filters (twice a year for us), and when my machine played up a few months back, it was less than fun getting it down the attic stairs to have a full inspection. If possible, I would look into placing the unit in a closet or wardrobe on the first floor. I wouldn't be greatly concerned with the balancing between floors since the overall balance is correct, but, I would also possibly have a look at having two machines, one upstairs, one downstairs. As you can opt for smaller units, the price may be very similar, but gives you more overhead if you want to run higher rates than those listed without much stress on the units.

Apologies for the rude statement, i would like to edit this to state that this is my experience with SOME plumbers, and it is clear based on this forum alone that there is a huge difference in how some wish to operate! I have no doubt there will be plenty of plumbers who would be happy to work of a design and also provide input free of charge, like several on here who have given their time and knowledge for no financial gain, but they are just tough to find in my area! I will endeavor to keep hunting!!

Plumbers have very sensitive ego's, they seem to struggle to do what the customer asks, let alone take some other mans seconds...

I feel your pain @Jimbo37, based in Donegal and finding it very difficult to get anyone to "design"! I think we have had maybe 1 reputable installer so far ask for heat loss, and i asked a couple of others if they would not need to know heat loss, one answer was that he uses 40W/m2 for new builds. Thats at 25 deg temp difference, and maybe is not terrible, but my calcs for 25 deg is 15.9W/m2, so would be some what overkill to install a heat pump to hit 40! One of the main challenges I have found, as others have also stated, is getting a machine as someone not in the trade. A couple of plumbing supply stores will sell me a machine, told me they wont give me the same price as the plumber (odd) but that it will be sold as seen, zero warranty. I have had a little more luck with commercial refrigeration companies, e.g. a company based in Donegal told me that they will sell me a Daikin unit, and if I have their engineers commission and do an annual service then they can provide the full 7 year warranty. There is options out there, just a PIA to find! I am trying to work with some local plumbers and take an active role in design to see can I find a happy medium, but may end up a DIY job yet

Great information, maybe I am naive but that seems like a great result, free daytime PV running the HP in cooling mode and seeing upwards of 5 degc temp offset, id be delighted with that!

Nice point on insulating loop feed lines, would never think on these things! Is handling which area gets flow first just position on manifold? all very interesting, I have yet to get into too much detail on the cooling side! Main factors so far are the solar gain redistribution and opting for a heat pump (if possible) with a cooling function. On that note, again on pipe spacings, using flow rates and pipe spacing to help not over heat areas with higher solar gain seems clear, but on the flip side, when it comes to cooling the slab by pumping around 13-16deg C water, would it not be a plus point to have more pipe, i.e. less spacing? The principle that the more water in the slab will allow for more heat extracted? Having pipes at 300 centers are bound to be less efficient at cooling the slab than at 100mm? I am sure there is maths that can be done on how much heat can be extracted by volume of water i guess

Thank you very much @SteamyTea that all makes sense now! Will try do some calculations and see where that leads but open to the idea of using different spacings now! I assume, if rooms do not share loops, a portion of this can be achieved by adjusting flow rate for each loop? From what I have seen though, the controls on this are not exactly fine, so I guess you wouldnt want to be relying on this as your only way to control it, thus the need for different spacings?

Ok so during shoulder months and I assume summer, run the pump during sunlight hours to help circulate the solar gain? This is very interesting and first time I heard this perspective. If I'm right then basic principle is that the risk of defrosting is much greater when the ashp is working in dhw and much less risk when doing central heating temps regardless of the load? So to help this one should try avoid having the ashp heat the dhw? Is that the general idea? An example of the setup, say for Nov - Feb, reduce the ashp set point for dhw way down, and set a timer switch to bring on the immersion during night rate electricity to top up the tank to a modest set point of say 50c, and have pv add input whenever it can? Sound about right? What sort of oversizing of uvc would you recommend?

Great to hear! In your photocell example, does that mean that when the ASHP runs at night you are not running the manifold pumps? Help me understand this, if each room has one large window then for sure solar gain will be different, but assuming the same fabric, losses will be pretty close to each other no? So since from a heat loss perspective would the emitter size not be the same? I appreciate if you can accurately map solar gain then you could decrease the emitter size appropriately, but not seeing the downside to keeping them the same? This is backing the concern with using room based stats at all, but I get stuck with the idea of maybe sometime for some reason liking or needing to have the ability to set room temps independently from each other, e.g. trying to keep a bedroom at 18/19c v centralized living at 21c. Think I will just have to come down on one side at some stage Interesting, yeah was pretty set on mixer valves based on reading here!! I guess I could still achieve the solar gain redistribution with a 2 way valve and pump. Would never have thought a bleed would have such an impact, and once you removed mixer you found 26c ashp output and 26c input at manifold?

Thanks @ProDave, why always a 2 port valve for each manifold and DHW? (ignoring solar gain redistribution). Would the one for DHW not be surplus to the valve controlling heat V DHW? House is single storey but in 3 connected blocks so hoping I can treat it as a single input for heating, and allow for solar gain redistribution within each manifolded area, i.e. east side of house & west side of house. Appreciate your point on general answers, learning from this thread and others that there is more difference in ASHP controls between manufactures than I was expecting!! I will be sure to get into more detail once we have downselected the manufacturer we want (can get)! Tbh I am struggling to make sense of any solid calculations to know for sure which is the ideal spec, but I have used Jeremys spreadsheet for total envelope loss, and spent some time in loopcad doing this by loop etc. (I do need to fine tune this) Re. pipe spacing, while I appreciate it may not be strictly needed and not be the most cost effective route, I am struggling to see why I would not default to 150mm pipe spacing; It will allow for larger volume of water so that either manifolded area would be less dependent on the need for a buffer My understanding is the more water in the system available to output heat, the lower the water temperature can be With the kore insulated raft foundation, the is much larger than standard volume of concrete, acting making me think that having a large heat emitter running at low temps is better? These may not be great reasons, but on the otherside, I dont know what the downside to taking a cautious approach to this is, outside of cost of materials, labour at installation, is there any drawback to smaller pipe spacings? Thanks @JohnMo I think my two manifold areas can be 120m2+ each (house 265m2), so im hoping that by taking the volume of water in the smaller of the two manifold zones and using that as the basis to require/size a buffer. Note taken on WC, makes sense! Can I ask how the pump and mixer was causing a drop in temp? Is the point of the mixer not to set the temp for all loops on that manifold? Is it in the response time that you seen an improvement then? And (assuming you have an upstairs manifold and a downstairs manifold) did you remove both pump & mixer from both manifolds or just one? Sorry if this is a simple question! Thanks for this @Temp this was my thinking based on previous experience with a gas boiler system, but I had assumed (again prob incorrect thing to do) that this would not be an ideal setup for a low energy build? I would have thought I wouldnt want to give any single room the ability actually turn on the ASHP in order to prevent short cycling? My thinking on what would be expected for this type of system; North facing room drops below room stat set point, opens manifold loop for room. Manifold pump is triggered, pumping open loops in this manifold combined with now open north facing room. If north facing room takes enough heat out of open loops then this will drop the temp in these zones, where a centralised house stat lives. Only when this centralized stat drops below its set point (meaning that the whole manifold zone is at or below this temp) then will the ASHP trigger? I was thinking the alternative would be to remove the room based stats completely and have either 1 centralized, or 2 (1 within a central point in each manifold zone) call the ASHP, assuming that the heat distribution within the zones will work itself out? Seems to be others on here who start out with loads of room stats but end up removing them. I have been using Jeremys calcs for whole house and then loopcad as a starting point for each "room", but I am thinking I will do a more exact room by room sheet alongside loopcad in the coming days! @PeterW Am I right in that you suggest this as it is really the more fool proof option? Meaning that while it may not actually add any efficiency to a well designed system, it will help an otherwise poorly designed system? Second question, since the stat on the buffer is reading water temp v room temp, im guessing that this is either accounted for in the ASHP controls or do ASHP controls typically have input options to state that the stat is reading water temp v room temp? Suppose what I am wondering is does this make it a little bit trickier to set room temp, as there wont be a direct match from the buffer temp to the temp we want in room? If I want to set a room at 21c, I cant tell the ASHP to look at the buffer stat and heat it until it 21c right? This will be a different number... Third question if I may, I have been looking at UVC's and looks like we have 3 priorities to hit, 1 - Coil size suitable for ASHP, 2 - Element location for PV (bottom of tank), 3 - Volume for our usage. I seen the, for lack of better phrase, "combi" cylinders which have both UVC and buffer in one, e.g. https://www.jouleuk.co.uk/pre-plumbed-heat-pump-package-w-buffer/ While this option looks to be a no go based on priority 2 (location of element for PV), assuming that such a tank exists that meets the 3 priorities and has an inbuilt buffer, are these a good option, or do you typically always opt for a stand alone buffer? Last question on this ha, any logic in having a buffer with an element connected to a secondary PV output?