@mikeh Methinks there may be room for improvement in fitter training then. Toodles.

Hello this forum, and thread in particular, has been a fantastic resource for my Aira heat pump research. I've been quoted for a 8kw pump with 250l tank & 40l buffer.

A couple of things initially made me hesitant:

First of all, they would not install the 250l cylinder in the loft. I've plenty of space up there and it would intrude in a room downstairs. However, this week they informed me that they have a new product that will fit in the loft. They've been loosing customers over this. 

Second - I'd been advised by others to not have a buffer tank. I spoke to Aira and they insist on this. I assume they do so to help prolong life of pump and therefore make them more comfortable of warrantying it for 15yrs. However, reading previous posts (Thank you to those for documenting their experiences) I'm less bothered as long as it's installed correctly. 

Any thoughts on a designed SCOP of 3.96? House has a large room with significant heat loss and some 10/15mm piping to radiators. Also - they have designed the pump to run at 47C - is this going to be inefficient? 

I'm in Scotland, so a bit colder and damper than south of England.....

@borderbloke I wonder if the new product might be the heat pump DHW tanks being marketed as Heat Geek designed? These tanks are, as I understand it, somewhat smaller than many current designs are. I don’t know whether the capacities are acceptable to fit MCS guidelines though - anyone? Adam Chapman was extolling them recently (they don’t manufacture them themselves) and demonstrating that even the smallest model could provide several showers and be ready for more demand soon after. Regards, Toodles.

@borderbloke I was thinking similar to Toodles. Aira have partnered with Heat Geeks. Regional Aira teams have a go to contact for tricky installs and have offered their installers access to the heat geek online courses. This is a big plus for Aira installs if you ask me. Heat Geek have come up with a mini cylinder/store that works more like a combi boiler for instant hot water, for jobs that are not suitable for large cylinders. Have a look at this Video

It may be worth asking Aira directly if they plan to fit a Heat Geek mini store solution.  

@mikeh Yes, the mini stores might have been a solution for me in 2022 - had they been on the market when I was researching my ASHP project - same problem, not enough room for a standard cylinder. Regards, Toodles.

I think they mentioned they are now fitting a hydrobox with a separate cylinder. 

@borderbloke Did you hear this from Aira, any idea on the size of the new offering?

I've been offered the 100l tank by Aira and they originally said it would provide 16-20 mins hot water which didnt sound like enough for 2 showers to me. They've rowed back on this now and said it heats as soon as the temp drops a couple of degrees so you will get "enough" hot water. But i'm a little worried about the tank capacity especially as other manufacturers are usually in the 150l-200l range for a 2 bed house. I know there is a "boost" mode to give more hot water at the expense of efficiency but not sure how much this provides.

Any thoughts on the 100l tank capacity by people who have had one installed? My other option is a Vitocal 151a which is a good looking bit of kit with a more reassuring 190l (but an extra £1660.)

@paddy welcome to the forums.

Your concern about the 100-litre tank is understandable, particularly for households needing consecutive showers. From experience, a 100-litre tank can provide around 12-15 minutes of hot water at standard shower rates (around 10 litres per minute), so two showers might stretch its capacity. While Aira suggests the tank reheats when the temperature drops by just a couple of degrees, this approach can be quite inefficient for an air source heat pump.

We set our own 300-litre tank to a 15°C differential to allow for longer, more efficient reheats. With a wider differential, the ASHP runs in its optimal range, delivering longer, more energy-efficient heating cycles.

Regarding water temperature, another factor is the set temperature of the hot water cylinder. We heat our water to 44°C to minimise blending with cold water at the tap and it works in a range our heat pump is comfortable in. This ensures that the hot water is used as efficiently as possible. Many tanks are set to heat water to 55°C-60°C, but at higher temperatures, the system will require more energy to maintain heat using the immersion if it’s a low temperature unit. Unfortunately, we don’t know what Aira’s default set point for hot water is, but that’s something worth discussing with them.

For ASHPs, efficiency drops significantly as the target temperature increases. ASHPs are most efficient when heating water at lower temperatures (40-50°C), so keeping the set point reasonable will help balance comfort and efficiency. If Aira’s system defaults to a higher temperature, you may want to have a conversation about lowering it to improve your system’s overall performance.

Generally, larger tanks (150-200 litres) are recommended for two showers, especially for homes using ASHPs, as they allow the system to operate more efficiently with less frequent reheating.

@paddy I presume that Aira are offering you the 100L tank + 40L buffer tank combination, so using @Mars rule of thumb you will be getting 16-20 mins of constant hot water. I don't know if they specify a 100L + 100L option, or whether this is sensible. We have a 4 bed house and have recently had an 8kW + 250L + 100L installation by Aira. Our biggest consumption of hot water is for baths, we still use our 7kW electric shower. 
The Aira app allows three settings for the hot water. Mine tells me that Eco saver (50°C) will give me 35-40 mins of hot water, Standard (55°C) 40-50 mins, and Luxe (65°C) 45-55mins. The installer recommended using Eco, which I have done and we haven't run out of hot yet. I did have to call Aira back to tweak the set temperature to make the temperature out of the tap a little warmer as initially there was no need to mix cold water in at the bath tap for a comfortable soak.
Hope this helps.

thanks! I just spoke to Aira and the buffer isnt used for hot water apparently, only on the central heating side of things. I'm waiting on confirmation of the different hot water temps one can select for the 100l tank and will provide that here in case anyone is curious. They also told me the tank has a "boost mode" which uses a little immersion heater to heat the tank quicker in. Obviously at a massive efficiency penalty but useful once in a while.
They also confirmed the hysteresis is only a few degrees so the heat pump will start heating the cylinder again once some of the hot water has been used which stretches that 16-20 minutes out a bit (again at a bit of an efficiency penalty).
I take @Mars point about ideally heating a greater volume of water to a lower temperature for efficiency but I guess its a trade off, if the 100l tank is enough hot water most of the time then its probably using less energy overall than if you were "More efficiently" heating 250l of water to a lower temp.

Following on from my issue with poor flow through a few radiators and likely following on from a poor Trustpilot review. Aira have been out this week to reassess and rectify some existing pipework. 2 engineers have spent 2 extra days upgrading an extensive section of 15mm plastic push fit pipes, from the new cylinder location to where the existing 22mm pipes connect up to the old boiler location. This was seen by the new engineers to be a bottleneck in the system. We now have new 28mm lagged copper pipes that bypass the old 15mm. This runs from the utility room, through the dining room at floor level, into our cellar to meet the existing 22mm pipes. Due to the tile floor and an inaccessible ceiling void, this was the only way to run the pipes. They have made a neat job and will not take much to box in, using the salvaged skirting board. It's too mild outside again to really tell the difference yet. But when they jacked up the flow temperature to test the radiator performance, we got all rads evenly warm across the top which was much better than before. The upgrade has also meant the pump next to the buffer tank has now turned down and isn't needing to work at 100% which has reduced the rushing noise in the plant room. I have to say I am very impressed with the extra level of service I have received to help improve the performance of my system. Images below are of the completely new pipe run installed.

Hi. I too am about to get a technical survey so the thread has been very useful. It’d be nice to know if Aira would provide you with the 12th month SPF (seasonal performance factor) which shows real efficiency of installation not just the pump, rather than the ASHP SCOP ( which is a very poor proxy for efficiency)or whether you could fit kit from heatpumpmonitor.org which gives comparative data for various installations across the country ( forgive me if this is already familiar to you all)..
I’m somewhat encouraged by Aira’s seeming desire to sort things out and to monitor and fine tune the system going forward, tho like Mike not keen on being a Guinea pig/ early adopter but thanks to those of you who are, and for sharing your experience.