Gav_P Posted August 24, 2020 Share Posted August 24, 2020 Hi all, it’s been a while since I’ve been on the forum, as I’ve been working away for quite some time... Now I’m back home I’m thinking about replacing my radiators upstairs as they weren’t great at doing more than keeping the chill off in mid winter (They are standard steel rads). I have a 5kw ASHP delivering to the upstairs radiators, UFH downstairs and HWC, and general cooed very well for a average build standard of property (not eco build). I need the radiators to be able to deliver more heat from the low temp of the ASHP... what options do I have? Has anyone used one of those fan assisted low temp radiators? Are they worth the incredible price? Are they noisy (considering they will be in bedrooms). Any advice or general opinions greatly received. :) Link to comment Share on other sites More sharing options...
Hobbiniho Posted August 24, 2020 Share Posted August 24, 2020 First question, are the radiators single panel or double?. I have panasonic air rads downstairs and normal steel panel rads upstairs, mine are double panel and quite "big" for the size of room, i would not want air rads running in a bedroom when im trying to sleep, i basically cant hear my ones downstairs but there is other noise, tv, dishwasher, fridge etc. if you think you can program it so that the heating isnt on when your sleeping then air rads are good at what they do but as you said they are expensive 1 Link to comment Share on other sites More sharing options...
Alexphd1 Posted August 24, 2020 Share Posted August 24, 2020 If they are single i would go double, if double i would go treble panel. If going going single to double (double internal fins) it doubles the surface area so double the heat output. 1 Link to comment Share on other sites More sharing options...
Gav_P Posted August 24, 2020 Author Share Posted August 24, 2020 Ah ok thanks. I have quite large doubles already. I’ll give treble a go first, as they are much more reasonable priced. what’s the deal with steel vrs Ali ... is there any benefit to be had in different materials? Link to comment Share on other sites More sharing options...
Miek Posted August 24, 2020 Share Posted August 24, 2020 Look up the datasheet for the radiators. You can find the heat output for different temperatures and get an idea of how big you need to go. Obviously you need to know what temperature you are running your system at. The relationship between heat output and system temperature is non linear so you need to have a lot more radiator surface area than you might expect, toughly triple what you would need for a gas system running at 70 degrees C. Link to comment Share on other sites More sharing options...
Gav_P Posted August 24, 2020 Author Share Posted August 24, 2020 I’m running my system at about 42 at the moment... although I could crank it up a bit if I managed to find myself a command unit for my kingspan (Aka carrier) ASHP. After taking a look at what my current rads are (double rad with double fin) rated at approx 2.1kw (assuming I was heating them normally with gas or oil) in a room requiring 1kw. ... so I either replace these with something that is more efficient or increase the output of the ASHP a bit I guess. Link to comment Share on other sites More sharing options...
PeterW Posted August 24, 2020 Share Posted August 24, 2020 Or you could just run the rads for longer ..?? As long as the KWh input is greater than the kWh loss from the room then it will heat the room. Link to comment Share on other sites More sharing options...
joth Posted August 25, 2020 Share Posted August 25, 2020 (edited) 8 hours ago, Gav_P said: in a room requiring 1kw. .. How many rooms do you have? If a single room demands 1kW then I think it's the 5kW ASHP itself that'll quickly become the limiting factor. (My whole house has a heat load of 2kW on PHPP and we're still planning on 8kW ASHP but that's for faster UVC reheat times) Edited August 25, 2020 by joth Link to comment Share on other sites More sharing options...
SteamyTea Posted August 25, 2020 Share Posted August 25, 2020 Q = k×A×ΔT Where: k is the coefficient of heat transfer of the heating device (W/m²×°C) A is heat transfer surface area of the heating device (m²) ΔT is the temperature difference (°C) You really need to know the room by room thermal losses before you can start to work out radiator types and sizes. Link to comment Share on other sites More sharing options...
Gav_P Posted August 25, 2020 Author Share Posted August 25, 2020 1 hour ago, joth said: How many rooms do you have? If a single room demands 1kW then I think it's the 5kW ASHP itself that'll quickly become the limiting factor. (My whole house has a heat load of 2kW on PHPP and we're still planning on 8kW ASHP but that's for faster UVC reheat times) Yeah it probably is.. I bought it on eBay a year before I even started the renovation and extension, figuring it was worth a punt at £250 (new).... and it was definitely worth it. I’ve got 4 radiators on the system, and I have calculated their demand for the first time this morning... I need 3.5kw for upstairs plus whatever the ufh needs downstairs. Link to comment Share on other sites More sharing options...
Gav_P Posted August 25, 2020 Author Share Posted August 25, 2020 40 minutes ago, SteamyTea said: Q = k×A×ΔT Where: k is the coefficient of heat transfer of the heating device (W/m²×°C) A is heat transfer surface area of the heating device (m²) ΔT is the temperature difference (°C) You really need to know the room by room thermal losses before you can start to work out radiator types and sizes. you lost me at Q. ? Link to comment Share on other sites More sharing options...
Gav_P Posted August 25, 2020 Author Share Posted August 25, 2020 I may start looking for a bigger ASHP. Link to comment Share on other sites More sharing options...
Hobbiniho Posted August 25, 2020 Share Posted August 25, 2020 How did you figure out your heat losses for each room, you should search for j harris spreadsheet, this will figure out the heat losses for each room then you can select a suitably sized "emitter". Also 42 degrees flow temp is quite high for an ASHP, mine is run at 36 but the emitter size was calculated for 35 flow temp, so if you are struggling with quite a big radiator and a 42 degree flow temp, a bigger ASHP isnt going to make much of a difference, is the current ASHP delivering the flow temp reliably? Link to comment Share on other sites More sharing options...
Gav_P Posted August 25, 2020 Author Share Posted August 25, 2020 I used a basic calculator on a radiators manufacturers website... so probably not perfect but gives me something to consider regarding what losses I have to counter. My difficultly is understanding how much heat I am putting into the room (or not as the case is). I think I need to run it (when the weather gets colder) without the downstairs UFH on so the ASHP is only delivering to the rads and see if it can cope with that. ... I maybe just asking too much from my little HP. Link to comment Share on other sites More sharing options...
Gav_P Posted August 25, 2020 Author Share Posted August 25, 2020 To be fair I haven’t really monitored the output of the HP, I’ve just plumbed it in switched it on and bingo it worked... so maybe I need to take a look at managing it better. ? Link to comment Share on other sites More sharing options...
Gav_P Posted August 25, 2020 Author Share Posted August 25, 2020 I have just realised my fundamental error ... my HP is 4kw not 5. ??♂️ Link to comment Share on other sites More sharing options...
joth Posted August 25, 2020 Share Posted August 25, 2020 3 hours ago, Gav_P said: I may start looking for a bigger ASHP. Depends how off-piste you want to go with this, but if it's only a few days per year you need the higher capacity you could put a Willis heater inline with the output of the ASHP and use to boost up the temperature a bit. For £50 it could give you 8kW on cold days. Link to comment Share on other sites More sharing options...
Gav_P Posted August 25, 2020 Author Share Posted August 25, 2020 1 minute ago, joth said: Depends how off-piste you want to go with this, but if it's only a few days per year you need the higher capacity you could put a Willis heater inline with the output of the ASHP and use to boost up the temperature a bit. For £50 it could give you 8kW on cold days. Funny you say that... I was trawling through my old posts and it reminded me that I have already put a willis heater in (but as a bypass to the HP when I broke it). So maybe I should reconfigure it to be inline (with a second one to meet flow rates) . it’s certainly the cheapest upfront cost... and easiest to get working. Link to comment Share on other sites More sharing options...
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