Jerry32

Thanks for the replies given, as they essentially back up my thoughts entirely. I'm pretty sure that as the Installation company that fitted the really neat / tidy installation in the village, used a volumiser, not a buffer tank, on that installation, I'm hoping I can reinforce this approach on his next visit. ( It's a small firm, owner owned, and he seems to have a handle on all the questions I asked of him, unlike several other firms, which seem to think they can tell you what they're going to fit in your house, even before they've site visited or done any calcs ! ) My 80kW per day is the highest total daily LPG usage during the last two winters, but, it's not because we have a near passive style modern house, it's because I know how to put on a jumper when required ! I've been running our LPG Combi boiler 24/7 during the 4-5 months of winter, but with the output temperature ramped right down, on/off firing at 28/38 degs C, which for all but the worst winter days, keeps the house above 18 degs C. That's warm enough for us. But the standard MCS calcs do not allow for personal preference on house temperatures, and if the OAT is 8 deg C, IAT is 18 deg C, then if you try and increase the IAT to 20 deg C, that's a 20% increase in LPG / Energy input requirement. i.e. if we ran the house to try for 20 deg C IAT, then that 80kW pd becomes 96kW pd. Even so, as I've tried to explain to so many other installation companies, 96kWh / 24 hours, does not equate to anything like a 12kWh ASHP requirement. One installer even wanted to fit a 16kWh ASHP. This was why I also requested information as to whether 2x smaller ASHP's could be installed, so that for most of the heating season, I'd really only be running one of the two fitted ASHP's. In Offshore Installation terms, fitting two dissimilar output 'units' gives maximum flexibility, i.e. a 4kW and an 8kW, gives 4 or 8 or 12kW max outputs, and all the modulated down capabilities in between, and probably down to 2kW as well. I'd really like to know if 'Sharpener' managed to get the information he posted, from the Vaillant control panel, as I could take the people a bottle of wine, just to get to find out if their system does the same as his ?

Hi Sharpener, I'm hoping you might still be looking at build hub occasionally, as I'm really interested in your initial information on the Vaillant Arotherm Plus 12kW ASHP. I'm almost certainly going to be 'recommended' to have fitted at least a 12kW ASHP, the same model as yours, because that seems to be the way of the MCS heat calculations, even though with an LPG Combi boiler, I've never used more than 80kWh on heating, in any given winter day, during the last 2 years. I'd contacted Vaillant Tech Support, and to my surprise, they have stated that the compressor within the Arotherm Plus range is not an Inverter driven one ? So I'm now even more confused, because you've managed to measure compressor modulation depending on the heat output required, assuming that the reduced percentages down from 100% means reduced power output / input. I'm concerned that I'm going to end up with an ASHP which spends a lot of time short cycling, and from just about every forum discussion I've read, this is definitely not going to help the COP. I've pasted in the reply I received to both my tech support 'requests', and am wondering what you might think of them ? The earliest is the first, the last is the latest, (opposite to email style presentation). ----------------------------------- Hi, I've been in contact with Swift Renewables in Clevedon, Somerset. As I've seen a really competent Vailliant installation in the village, completed by their company. They are going to do the MSC heat loss calcs, and I know it will come back with probably a 12kW ASHP as a minimum. (Even though I've calculated from the last two years, my winter time daily energy heat usage is a maximum of 80kWh per 24 hours.) If I'm 'coerced' into having a 12kW ASHP, (to meet MCS requirements / Govt grant etc.), is there any reason why this could not be a 5kW & a 7kW ASHP, running either one, or both, depending on the heat output required at the time? I'm really concerned that a solitary 12kW ASHP is going to be short cycling for a large majority of it's use, as it would only operate 'properly' during the very worst cold spells (we live in lowland Somerset, we don't do snow as a rule). This is going to kill the overall COP efficiency of the ASHP. What is the minimum power output of your various Arotherm Plus ASHPs ? Can they all run with a volumiser not a buffer cylinder? This is another concern for me, why do I need to run a separate circulating pump? When the ASHP has it's own circulating pump already. What is your recommended volumiser cylinder size for each of your ASHP's mentioned above? I believe it relates to the ability to successfully defrost the ASHP, so presumably it will be different for 5, 7, 12kW ASHP's? I think I've finally found a competent installation company, who will fit an up to date efficient Vailliant Arotherm Plus based system for me. (I'm an ex Offshore Oil & Gas Dept Head, you might be really surprised at how many Installers do not know the simple basics of heat retention / Transfer, they just want to fit whatever 'kit' they always have fitted previously ! ------------------------------------- Hello, Apologies you did not hear back last month, I can only assume the email got lost somehow, as we aim to respond to all emails within 24 hours. In terms of your question, as a general rule we do not advise cascading different size heat pumps. The concern is that having different build confused the EBUS system enough to cause an issue with performance. Therefor, you are free to cascade several heat pumps, but only same heat pumps. In your case, 2 5kws or 2 7 kws, for example. There is a chance of cycling a little more than you would like if the unit is oversized dramatically, however any design should account for a certain avarage temperature, not for worse case scenario. In england the avarage is 0 degrees outside with 45 degree flow temperature. In terms of your question about minimum output, our compressor is not inverter driven, meaning a 12 kw heat pump will aim to output 12 kw of heat energy at all times, with mild outdoor conditions and a good install it can technically output as much as 16 =- example from manual being 2 degrees outside with 35 degree flow. Obviously the running costs lessen the milder it is, but yeah, the output increases, if anything. You are indeed correct that the minimum system volume is enforced for de icing reasons, minimum values for all our Arotherm Plus - 40L for 3.5/5kw 45L for a 7 kw and 150 litres for a 10 and 12 kw. Volumisers are more practical with smaller units whereas buffers are usually used in larger systems, we effectively do not care how you meet your minimum system volume, as long as it is met. In certain houses with large radiators ( and a few of them) minimum volumes can be met without any added volume at all. Kind regards, ---------------------------------- I've just read through your reply, and I'm slightly concerned about the comment you made, that the ASHP is not inverter driven, and that it will try to output 12kW at all times ? Surely the whole reason for having an inverter motor drive, is because for the vast majority of the time the heating is on, the required output will be less than the full 12kW capability ? Therefore because it will be overproducing heat for the majority of the time, presumably the house thermostat is going to have to stop the heat pump whenever the set house temperature is reached ? I'm sure I've understand the inverter driven theory correctly, in that the reason for an inverter driven compressor, is so that the actual heat pump output can be modulated down to eventually match the level of heat output required, so that the delta T (inside to outside temps), keeps the house at/near the thermostat controlled temperature ? So, how does the Arotherm Plus manage to modulate the heat output to maintain a set temperature ? If it's by switching itself off when the thermostatic temperature is reached, and then back on when the temperature falls, then that is short cycling, i.e. exactly what our present LPG combi gas boiler does ? It would appear from all the internet based sites, that repetitive short cycling is an inefficient way to operate an ASHP ? Best Regards ---------------------------------- Hello, Yes in our unit the inverter does not module the control output, but controls the electronics in general. The output of the compressor is not modulated down based on outdoor temperature does a supposed heat output requirement at the time, which is why the advice is to size the heat pump very accurately. There are some safe guards built into the software of the unit to avoid excessive short cycling but they are not really something I have in depth knowledge on as that would be sensitive internal information, however it was fairly public a few years ago that a software upgrade on our HMU board lessened cycling by 2 fold by more accurate calculating energy integral temperatures to decide when to activate/deactivate in heating demand. Kind regards,

Thanks for the reply above, and I've now done a bit of research into Condensing Mode, 'efficiency' versus 'gas usage' reduction. It appears that there is more in the way of gas usage cost saving, by reducing the output temperature from the boiler, so that it only 'just' maintains the house at the temperature you are comfortable with. (essentially manual weather compensation?) Rather than there will be by maintaining a higher output temperature to get a better temperature differential, output to return. So strangely, I might have lucked into the best cost saving mode last winter by keeping the boiler output temperature as low as practically possible. Hence the large reduction in the number of litres of LPG that we used. It was nearly 30% less. There's more than one article that I've read, that says condensing mode only really starts at below the ambient dewpoint temperature (which typically changes depending on the weather), but is generally below 55 degs C or less, and I'm well below that temperature, and the flue output appearance seems to indicate condensing mode was active. The other thing seems to be that the 2nd (condensing) heat exchanger in the flue, is there to preheat the return water before it goes into the main heat exchanger. This is exactly what I'm trying to achieve with the 'buffer' cylinder pre heating the return water. So I'd like to think I'm on roughly the right track. But, but, but, my mate 'The Plumber' has probably thrown a bit of a spanner in the works, as he's pointed out that if I use the UVC on the CH circuit, and then I eventually want to fit an ASHP after all of this, then the cylinder will really need to be put back into it's intended use, as a DHW cylinder, and 'we' (meaning him) would, as well as having to do a complete repipe, also need to flush out all the last traces of Fernox treated CH water from inside the cylinder. Before it's let loose on the DHW system. (No one wants a potentially Fernox tainted Hot Water shower). So, it looks like I might be taking in your original comments after all, i.e. Stop mucking about, and just set it up to use the excess Solar PV to heat up DHW water, and live with it that way. (I still might use it's internal high surface area heat pump coil, 3.3m2, as a bit of extra preheat on the CH return pipework, just to increase the duration between those Combi firing times). This following article, on condensing mode in boilers, was probably the simplest to read through of all the ones I'd found, i.e. no complicated thermo dynamics involved ! trustedreviews.com/explainer/whats-best-temperature-condensing-boiler-set Many thanks for all your comments, as it's certainly got me to where I needed to go in the end.

Hi JohnMo, I'd read some of your replies to other people, so was sort of hoping you might pick up on this thread, I don't know why the site wouldn't let me add a simple jpg, (I think it's worked this time.) 1. Yes that is my dilemma, but we use so little DHW in the kitchen / main bathroom, it's laughable really, hence my idea of flipping the usage of the main cylinder over to CH preheating use instead. In summer I'm pretty much resigned to leaving a fair bit of power up on the roof, but in winter due to the Octopus Flux tariff, I can mix and match cheap rate electricity, with any solar generated electricity, to keep the cylinder warm enough to delay the re-firing of the Combi. Well that was my intent anyway ? 2. I never thought of the condensing boiler efficiency to be honest, I'd only thought about delaying the re-firing of the Combi, so using less LPG than last year. We actually ran the boiler practically on minimum fire position last winter, it stops heating at 43, and fires again at 28 degs C on the Combi display. (The house is roughly at 18 degs C, which is fine for us). On sunny winter days, we don't always have the CH on constantly, just because of the passive solar heat through the windows. (Plus I've retrofitted shed loads of insulation / draught proofing etc.) I've not actually figured out whether those figures are return temp, heat exhanger temp, or outlet temp, but most days, it was firing for about 1.5 minutes, as the temp display slowly rose to 43, then off for about 1.5 minutes, as the temp display slowly dropped down to 28 degs C. (It didn't take us too long to realise, the now 17 year old, Bosch Combi 42Cdi when installed, was specced as per usual heating engineer calcs, and is way oversized for our usage). My assumption was if the water returning back to the boiler took longer to drop down to 28 degs C, then the firing cycles would be less often, ergo, saving LPG gas usage ? I've never heard of a Willis heater, but I'd originally thought about just using a simple 50 litre buffer tank on the CH return, with it's own Immersion heater to do much the same as above. Then as with most things, there is always a tendancy to get carried away, in this case trying to 2nd guess when / if we fit an ASHP instead (mission creep), and it ends up being a UVC of 200 litres and a bit of DHW heating / preheating thrown in for luck ? 3. I think I need to research the condensing mode envelope of the Bosch Combi 42Cdi boiler, as I was likely running it too low last winter, even though the LPG consumption reduction from previous years was pretty impressive. (LPG is expensive to be honest). 4. G3 etc. I probably didn't explain it that well, but my intention was to use the actual cylinder on the CH circuit, not the DHW circuit, so I'd made the assumption that G3 qualifications would not be required, as it's really no different to adding a radiator to the CH circuit ? (I'm not sure if my mate, a proper 'plumber' has G3, although he is quite used to my non standard ideas !) 5. I've managed to upload the 'back of fag packet' drawing this time, and I've allowed for a lot of isolating valves and NRV's, as I worked offshore in oil & gas, so do tend to like having loads of valves in a system ! Standing heat loss - I actually got the 2kWh per day figure from the Telford website, so I've been 'using' it in my calcs, but I bet it's no more accurate than the Ford / Fiat mpg figures for cars ? I have the feeling it was probably rated at 60+ degs C, and as you say, if the storage temp was lower, so will be the standing heat loss. I just haven't got to working out the reduction calcs yet. 6. I'm quite sure my mate would prefer me to do the simple setup, i.e. the DHW normal installation, but then he owes me a few favours, and I think he's well resigned to me overcomplicating things in the past, (as he's always said), but I do like 'proper traditional plumbing', along with loads of isolation valves, just in case for any potential 'issues' in the future. (I can't change the habits of my offshore North Sea lifetime, along with it's 'Oil / Gas' leakage paranoia ?) Would be interested if you think something like the drawing is in any way workable ? I already accept that realistically I've gone well over the top on the Solar PV system, but then the roof space is there, so what else was I meant to do with it ? Telford Heat Pump UVC rough setup in reverse mode.pdf

I've registered onto this forum, essentially just to ask opinions on this idea. I think I can use a Tempest 200L Indirect Heat Pump Cylinder Slimline – TSMI200HP/SL, in the opposite function to it's 'normal' setup. i.e. The cylinder will essentially be the last 'radiator' on the return CH circuit, where instead of emitting heat, I'm going to use the immersion heater element to 'preheat' the returning CH water, before it exits out the top, on it's way to the CH inlet side of the Bosch 42CDi Combi boiler. (i.e. A CH heatstore). The intention is to use up Solar PV power that at the moment is just being 'left on the roof', and help reduce the amount of LPG usage as well. In summer the Combi fire up on HW demand in the kitchen, for all of 30 secs is mightily inefficient. In winter, I'm only outputting a max of 45 degs C from the Combi to the CH radiators. So if I can preheat the CH return by just 5 degs C, that would be 25% of the work the Combi currently does. (approx 25 deg C return temp). If it turns out that it doesn't save that much LPG this coming winter, then I can always get it stripped back down, and setup in the 'normal' installation style and move to an ASHP instead, which is what this cylinder is intended for. (I'm kind of loathe to jump straight over to an ASHP, even though I know from last winter that my CH radiator system, is large enough to cope with a 40-45 degs C boiler output temp). The reason for choosing this particular cylinder, is that it also has the largest 'Heat Pump' coil at 3.3m2 surface area that I can find. As I also intend to use this coil to 'preheat' ('prewarm' more likely) any DHW water, before sending it to the LPG Combi, for onward DHW heating, mainly to the kitchen HW taps. My reason for reversing the usual setup, is that the LPG Combi is rarely used for DHW at all. It's main use is for CH during the 5 winter months. So it seems a bit daft having a 200 litre DHW store, losing 2 kWh standing loss per day, when we could really do with more stored energy used in the CH side of things. I've attached a sort of 'back of fag packet' drawing of the 'possible' cylinder setup. (well I tried to do this?) Does this idea make any sense to people on this forum ? The Duplex Stainless Steel spec used in the cylinder, and the 316L spec of the coil & fittings, should cope with fernox treated CH water ? I don't think I need to use the DHW expansion tank setup, as it's only going to be at 1.2 bar CH system pressure, and the Combi already has a CH system overpressure coverage ? The fact that it's not being used to store DHW, under pressure, I'm assuming means it does not need G3 installation either ? Are there any other pitfalls you can think of ? Reason :- I've massively overspecced my Solaredge DC PV system, 36 x 400W panels, 2 x 6kWh Inverters, 2x 10kWh Solaredge DC batteries, I'm on Octopus Flux tariffs, and my DNO export limit is set at 4.4kWh. So even on 'Sunny' Somerset's occasional gloomy days, there is quite a lot of power up on the roof, that the inverters do not need to convert to AC, because there is just no use for it. This is what happens when you've got too much roof space, and don't see the need to pay income tax on your savings ! Telford HeaTelford Heat Pump UVC rough setup in reverse mode.pdft Pump UVC rough setup in reverse mode.pdfTelford Heat Pump UVC rough setup in reverse mode.pdf