Nick Laslett

I found this piece of marketing from the MD of Oso. “A 300 litre Delta loses only 3.5°C in 24 hours” https://www.plumbingtrademagazine.co.uk/blog/OSO-Hotwater How true or relevant this is I have no idea. But I was looking for this kind of data to understand what kind of heat loss we should be expecting. I hope others find this useful, but please if this is a fantasy data point because of how heating systems really work, please feel free to make corrections.

I have a feeling that standing heat loss might be more important over the long term than coil length. These Telford’s appear to be ‘C’ rated according to the ERPs on their website. They loose double the amount of heat compared to the Oso, on a 300L UVC, 2.32kwh/24hrs vs 1.18kwh/24hrs according to the details here. https://www.tdlonline.co.uk/Heating/Hot-Water-Cylinders/Telford-Stainless-Cylinders/Telford-Tempest-Cylinders-Heat-Pump-Coil/6134-/Telford-Tempest-300-Litre-with-Heat-Pump-Coil-33sqm-TSMI300HP To be honest, I have no skin in this game. Until 2 weeks ago I was going to use a Sunamp UniQ12 for my DHW. I don’t need to make a decision on this issue for at least another 8 months. I only started reading about UVCs because my M&E person rubbished my Sunamp plan because he felt they were better suited to smaller properties. I especially enjoyed reading newhome’s thread about her Heat Bank and was glad that PeterW and NickfromWales were able to help her out. I think many people still find it difficult to understand what they need to consider for their Space Heating and DHW, adding UVC coil length as another factor is not going to help.

This thread also discusses coil length for HP. https://forum.buildhub.org.uk/topic/5510-help-me-find-my-hot-water-cylinder/ If I’m reading it right, there didn’t seem to be any firm conclusions. *I have levelled up and gained ability to edit my posts. Thank you forum gods.

What is more important the standing heat loss or size of heat exchanger? i get than one effects how long it takes to heat up and the other how long it holds the heat. The Panasonic only had a 1.5kw immersion, which seems equally tiny. Does the low standing loss off set the slow heat uptake?

Not sure how editing works, so had to quote my post. Viessmann in their ASHP brochure indicate that their UVC is appropriate for heat pumps, but on the direct website they offer the OSO Delta Geocoil. The rating for their 300L tank is similar to the OSO, only the 200L & 160L have the A+. I believe that what makes an UVC more suited to heat pumps is the length of the internal coil. In the 200L OSO Delta Geocoil the primary heat exchanger surface area is 1.4m2, this is from UK manual. I could not yet find these details in the Viessmann UVC documentation.

I’ve found an ‘A+’ rated UVC. Vitocell 300-V 200, seems a bit pricey compared to the OSO and Panasonic, also not appropriate for ASHP. As far as I can see as it does not have the longer internal coil. The 200L model has a standing heat loss of 0.75, which is better the the Sunamp UniQ9, which is their 200L equivalent. https://viessmanndirect.co.uk/Catalogue/Commercial-Cylinders/Vitocell-300-V-Type-EVIA-A-Single-Coil/Vitocell-300-V-200-litre-EVIA-A-White-Z016794

Thank you for the clarifications. Makes more sense now.

I assumed it worked exactly as you described. Does fitting something like a MyEnergi Eddi, make this more difficult?

Maybe I'm misunderstanding this statement. I assumed my PV in the summer would power the ASHP in cooling mode. Is that not the case?

It looks like Panasonic might have a rebadged version of the OSO UVC. https://www.aircon.panasonic.eu/_____/happening/sanitary-tanks/ https://www.saturnsales.co.uk/Panasonic-Hot-Water-Tank-300-Litre-PAW-TD30C1E5-UK.html Specs and pics look very similar. In any case another EEC ‘A’ rated UVC, energy loss 1.13kwh/24hr. Website says it’s anode free does not require any maintenance.

I think this is the post, that killed any remaining interest I had in the Sunamp.

Hello Eileen (or Nigel), how did you get your Sunamp and ASHP installed? Was it a package with UFH and PV? What size is your ASHP? Very torn between the simplicity of the Sunamp vs the comfort of traditional UVC domestic heating installation.

This is great info, thanks. I was only just reading @NSS thread Panasonic Air Rads Be Warned where his set-up had a low loss header, and there was good discussion about it's function. He was trying to get a higher temp to the air rad. According to the Panasonic Installation manual, with the simple 2-zone config I was looking at, it says that Zone 2 must be the same or cooler than Zone 1. I assume that this simple set-up will work in reverse when I need cooling in the summer? *Edit Just came across this interesting article on UFH regarding water temp and buffer tanks. https://heatpumps.co.uk/2014/03/06/getting-the-best-from-underfloor-heating/

Very good advice. I'm still at the pre-building controls submission stage. Trying to get the Foundation design finalised. Hopefully insulated raft with UFH. Based on various threads here, I have a very simplistic UFH design at present. ASHP does only UFH. Sunamps for DHW. 1 Manifold ground floor with 6 loops all 95m, 200mm spacing 1 Manifold first floor with 4 loops all 95m, 200mm spacing 2 zones: ground floor, first floor In Loopcad water temp 30 degrees, target room temp 23 degrees. (30 default in LoopCad, 23 hottest that should be need, actuals will probably be different.) I used JH's Heating Requirements spreadsheet and the heating requirements from Loopcad, the two figures were quite close to each other: "Total daily heat loss power for minimum OAT (W) 4147" The flow rate and Delta T were the main areas, I don't really understand. In Loopcad, if I set the Delta T to enforced fixed at 5 degrees, I get a flow rate of 1.42l/m on all circuits, giving a total of 15l/m flow rate. If I let the software calculate the Delta T, ground floor DT is 2.8 degrees with a flow rate of 2.4l/m. On the first floor the DT is 4.1 degrees and the flow rate of 1.6l/m, total flow rate of 18l/m. But I don't know what I'm trying to target, is higher flow better, is lower Delta T better. Reading lots on the web did not really make this any clearer. I was expecting the ASHP pump to drive the ground floor circuit at a constant temp set on the ASHP. For the first floor circuit have a mixing valve, pump and thermistor, with a slightly lower temp. This config is in the manual. I was not planning on having a buffer tank. I was happy for the ASHP to be on 24hrs, just hitting the target water temp. Obviously this is all hypothetical, and I enjoyed reading the various threads here and watching the LoopCad tutorials. At some point an actual Plumber will have to be engaged to make all this happen. These are just my research ideas.

Thanks, that is good to know. In Loopcad, changing from enforced Delta-T calculations to automatically calculated by the software, changed the flow rate on my design from 14L/min to 22L/min.