TonyT Posted August 8, 2023 Share Posted August 8, 2023 -3 at my area for design calcs, 22 deg in the bathroom, 21 everywhere else and 18 in bedrooms, if you know the construction make up you can do the heat loss calculations Link to comment Share on other sites More sharing options...
HughF Posted August 8, 2023 Share Posted August 8, 2023 1 hour ago, Post and beam said: Forgive my ignorance but if i want 21 degrees inside and work on an outside temp of -2 can you extrapolate what the requirement is. Isn't 21 and -2 the usual range? Your sap assumes 4.3 degrees for your location in the winter, which is a shit assumption. And the room temperature assumption comes from section 7, where the Mean Internal Temperature is shown… Link to comment Share on other sites More sharing options...
HughF Posted August 8, 2023 Share Posted August 8, 2023 You’ll need to model this in heat engineer, heatpunk, or the freedom toolkit so that you know your heat loss for those required temperatures. Link to comment Share on other sites More sharing options...
Post and beam Posted August 10, 2023 Author Share Posted August 10, 2023 On 03/08/2023 at 22:21, HughF said: Anyway, you need around 2.4kW to heat this place when it's 4.3 degrees outside So a 5kw heat pump will do the job ? 40% modulation would need to accomodate only .96 kW Link to comment Share on other sites More sharing options...
HughF Posted August 10, 2023 Share Posted August 10, 2023 1 hour ago, Post and beam said: So a 5kw heat pump will do the job ? 40% modulation would need to accomodate only .96 kW 5kW is basically the smallest you can get, so yes, I'd buy one of those. LG Therma V, Samsung Gen6, Mitsubishi Ecodan, Midea (6kW) Buy whichever one you can get for the lowest price, they'll all do the same job. Beware that Samsung units are cheap because the controller/indoor unit is an extra cost, and they need an external pump. Link to comment Share on other sites More sharing options...
Post and beam Posted August 10, 2023 Author Share Posted August 10, 2023 22 minutes ago, HughF said: because the controller/indoor unit is an extra cost, and they need an external pump. Noted and thanks. Link to comment Share on other sites More sharing options...
ADLIan Posted August 10, 2023 Share Posted August 10, 2023 Note SAP is a method of assessing energy use in a house in a standardised way; it should not be used as a design tool for hot water or heating systems. Link to comment Share on other sites More sharing options...
Post and beam Posted August 10, 2023 Author Share Posted August 10, 2023 57 minutes ago, ADLIan said: it should not be used as a design tool for hot water or heating systems. Every company i have spoken to regarding ASHP & UFH supply and install has expected to see my Sap report. For a house that does not yet exist what else are they going to use. Or me for that matter? Link to comment Share on other sites More sharing options...
joth Posted August 10, 2023 Share Posted August 10, 2023 I think the MCS song sheet says you have to use the MCS room-by-room calculation method. The SAP report likely has the necessary input data to plug into that other calculator, so maybe the easiest way for and ASHP supplier to bootstrap their work Beware MCS method assumes 5 ach and no MVHR, and it's hard to get installers to override that. Obviously going for a non-MCS install is one option! Link to comment Share on other sites More sharing options...
Post and beam Posted August 10, 2023 Author Share Posted August 10, 2023 (edited) I had an attempt to use the heat loss calculator kindly available here. I have no idea what good looks like so please critique what i have done. I aimed for 21 c room temp with a range from -7 up through -2, 0, 2, and a few others for the OAT. With reference to whether my designed air change value is 5, 3 or .3 The sap summary sheet (Building Regulations England Part L (BREL) Compliance Report) deffo uses .3 Heat loss - Caxton j 10 Aug 23.xls Edited August 10, 2023 by Post and beam Mention of the .3 ACH Link to comment Share on other sites More sharing options...
JohnMo Posted August 10, 2023 Share Posted August 10, 2023 Be realistic with you air changes 0.3 isn't, even with passive the notes say use 0.6. Even using 1 you total heat required is circa 3kW. So you need a dinky ASHP, 5 to 6 kW gives plenty of room for DHW. Just watch the volume of water engaged in the system or add a volumiser to the return leg. Link to comment Share on other sites More sharing options...
Post and beam Posted August 11, 2023 Author Share Posted August 11, 2023 12 hours ago, JohnMo said: Even using 1 you total heat required is circa 3kW. thanks. The SAP report is pretty close to this version which is comforting. A previous reply said that the SAP report should not be used to scale the heating. 12 hours ago, JohnMo said: Be realistic with you air changes 0.3 isn't I do agree it seems very low. But, the full Sap report and the 2 page summary report that came with it uses this figure everywhere. I have asked the TF to comment. Link to comment Share on other sites More sharing options...
Post and beam Posted August 31, 2023 Author Share Posted August 31, 2023 On 10/08/2023 at 20:24, JohnMo said: Even using 1 you total heat required is circa 3kW. I have changed the ACH to 1 and also the window U values becuase i have negotiated TG for the price of DG previously. Please critique this version for me and pick out anything that looks to be unrealistic. For example at cell D56. 14 represents a room temperature of 18 with an outside temp of 4 degrees C. Giving 1.59Kw requirement at Cell D65. And at H56, 28 represents 21 C room temp with an outside temp of -7 which i believe is the usual extreme used. This gives 2.87 at H65 Does this really mean that i only need a heat pump output of 3kw? Heat loss - Caxton j TG 31 Aug 23.xls Link to comment Share on other sites More sharing options...
JohnMo Posted September 1, 2023 Share Posted September 1, 2023 (edited) Looks ok. Couple things to consider, cylinder heating time, that needs to added into the mix and possible defrosts. I have a similar heat load, a 4kW is a little tight on capacity, so I have a 6kW (super cheap, very efficient), but as @HughF say a 5kW is fine also. You just need to ensure you have enough water engaged to stop short cycling (about 50L). Edited September 1, 2023 by JohnMo Link to comment Share on other sites More sharing options...
DanDee Posted September 1, 2023 Share Posted September 1, 2023 59 minutes ago, JohnMo said: Looks ok. Couple things to consider, cylinder heating time, that needs to added into the mix and possible defrosts. I have a similar heat load, a 4kW is a little tight on capacity, so I have a 6kW (super cheap, very efficient), but as @HughF say a 5kW is fine also. You just need to ensure you have enough water engaged to stop short cycling (about 50L). I think this the perfect example where a HP should start a heating cycle until, instead of stopping just to start again 5 minutes later, it should switch to minimally heat the colder end of the DHW, until the radiators loose some more heat, so on and on and on(not forever, but you get the point). Keeping the DHW at low charger during day with planning of the time when bath/showers are to be taken(set time frame) Link to comment Share on other sites More sharing options...
Post and beam Posted September 1, 2023 Author Share Posted September 1, 2023 7 hours ago, JohnMo said: You just need to ensure you have enough water engaged to stop short cycling (about 50L). So the principle to be aware of with 'engaged water' is a minimum quantity and not a maximum ? I think it might be 64 Litres in my case. Another variable i am interested in is the return temperature. If my house is well insulated and the 150mm pipe centres and 35 degree flow temp work out well is there an issue with the water not losing enough heat ? I read somewhere that this can cause its own issues. Link to comment Share on other sites More sharing options...
JohnMo Posted September 1, 2023 Share Posted September 1, 2023 Engaged water is the quantity of always open to the heat pump circulation pump. So basically open loops. Doesn't matter about maximum. 2 minutes ago, Post and beam said: Another variable i am interested in is the return temperature. If my house is well insulated and the 150mm pipe centres and 35 degree flow temp work out well is there an issue with the water not losing enough heat ? I read somewhere that this can cause its own issues. 35 sounds hot I would only be flowing that at -9 and I am on 300mm centres. If you are not loosing enough heat, that is simple, you are flowing too hot or you don't have enough heating system engaged to absorb the heat. Turn down the temperature, or make circuit open at all times larger. Basics Heat pump flow temp is set by your setup either fixed or weather compensated. The delta T is also pretty much fixed. That will be in region of 4 to 5 degs. Heat pump gets a call for heat, circulation pump starts, heat pump reads the return temperature and adds heat inline with the pre defined Delta T, as the heat is absorbed into the floor or room, the delta T will drop, so the heat pump adds more heat. It will continue doing this until it hits the target flow temp, plus a small amount (0.1 degrees or so) it will then shutdown the heat, but continues circulation. Once the return has reduced to a defined level maybe 5 degs below target temperature the flow heating will resume and keep repeating this pattern until the call for heat is cancelled. The more system volume and house available to absorb the heat, the longer the process between cycles takes. The process should take a minimum of about 10 mins for the heating cycling. Depending on the heat output versus heat required, the off cycles could be very long. Link to comment Share on other sites More sharing options...
Post and beam Posted September 1, 2023 Author Share Posted September 1, 2023 39 minutes ago, JohnMo said: 35 sounds hot I thought 35 was the lowest temperature that is usually talked about when flow temperatures are discussed. A target to aim down towards for good efficiency but not always achievable in some houses. Link to comment Share on other sites More sharing options...
JohnMo Posted September 1, 2023 Share Posted September 1, 2023 You have a modern well insulated house, your flow temp most of the time should be flowing sub 30, closer to 25. My heating curve is a flat line of 26 degs until 9 deg average outside temp, the flow temp then rises to flow temp of 35 degs at -9. Most the winter should be sub 30 degrees flow temp. Link to comment Share on other sites More sharing options...
Post and beam Posted September 1, 2023 Author Share Posted September 1, 2023 10 minutes ago, JohnMo said: your flow temp most of the time should be flowing sub 30, closer to 25 Well that can only be good for SCOP. I sort of thought that 35 was the lowest running temp for heat pumps, mainly because nobody seems to mention a lower figure. And thanks by the way Link to comment Share on other sites More sharing options...
DanDee Posted September 1, 2023 Share Posted September 1, 2023 22 minutes ago, Post and beam said: Well that can only be good for SCOP. I sort of thought that 35 was the lowest running temp for heat pumps, mainly because nobody seems to mention a lower figure. And thanks by the way https://heatpumpmonitor.org/ open every ufh system and see the flow temps around winter/spring https://emoncms.org/app/view?name=Heatpump1&readkey=8189ca75faaf0770d404461e8339448c https://emoncms.org/ecodantest2/app/view?name=My+Heatpump Link to comment Share on other sites More sharing options...
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