Heat Pumps: anyone have one/thought about it?

All you lot heating your hot water tanks to temps in the 40s are risking legionella,

The hw tank should be at 60oc minimum to stop legionella growing in your tank
 
Armageus said:
Which is why my tank uses an auxiliary heater to run a legionella cycle once a week (as I'd imagine most do)
Click to expand...
mine too

As the tank is at a lower temperature, you also cycle through the water much more quickly which drastically reduces the risk.

We heat ours once per day and by the end of the day, it’s pretty much cycled through so we pretty much cycle through so the risk of legionella is near zero even without that weekly heat cycle. The only reason I leave it on is because I’d probably forget to turn it on if am we went on holiday etc.

This video is worth watching for more info:
 
Last edited:
PermaChanged said:
As mentioned previously, we heat to ~48c and recharge when the temperature drops to ~42c based on the internal thermometers - that 6c recharge takes ~30 mins and we recharge twice within a 24hr period.

We could go for uber efficiency and choose to never recharge between certain hours, I can't imagine we'd drop temps particularly quickly from 42c to below comfortable shower temps given heat loss reduces more and more the smaller the temperature differential.
Click to expand...

Just had our quarterly electricity bill through, £36 for this setup as no heating used in that quarter - can't really grumble at that!

Also, in terms of savings, I made the switch from a gas guzzling 18mpg car to an electric van, that nets a £60+ saving per month at least!
 
Last edited:
The getting data out of the Daikin heat pump is a bit of a challenge. Energy usage is not the most accurate as it rounds to whole kWh.

I’ve got a little project for the weeks. To hook up an ESP32 to its internal serial port and a Shelly energy monitor for its power supply so I can export the raw data to home assistant.

According to the daikin app we used 48kwh heating the hot water for September including the legionella cycles. That cost me ~£3.36 as I do it all overnight at 7p/kwh. It’s in the ball park based on what I have seen from my solar system which is monitoring total house usage.

The gas standing charge alone would have cost double that.

I use cheap over night electric to do as much of the heavily lifting as I can rather than aiming for the highest possible efficiency as it’s cheaper to run. Hot water is done overnight and I heat the house back up from set back temperatures earlier and heat the house a little hotter in that period to make the best use of that 7p price electric.

If you were going for maximum efficiency, you’d do your hot water in mid afternoon when the air temperature is at its highest and the heat pump was getting some direct sunlight.
 
Here’s me just running mine to 55°c at 05:00 and 17:00.

Think I’m going to have to rethink that. I’m not on an eco7 tariff so will try heating it once during mid day and see if that’s enough for me.
 
55c is pretty hot for a heat pump, ideally you’d want it at 50 or below.

That does the mid-tank sensor get down to just before the reheat cycle?

Edit: for 55c you’ll be running at least 60c flow temps which will trash the efficiency, even for an R290 heat pump. I don’t think my R32 can’t even go that high without using a booster heater (aka direct electric).
 
Last edited:
b0rn2sk8 said:
55c is pretty hot for a heat pump, ideally you’d want it at 50 or below.

That does the mid-tank sensor get down to just before the reheat cycle?

Edit: for 55c you’ll be running at least 60c flow temps which will trash the efficiency, even for an R290 heat pump. I don’t think my R32 can’t even go that high without using a booster heater (aka direct electric).
Click to expand...

I’ve got a high temp one with a thermal store. Takes the water temp up to 75°c. It’s solely for DHW have air to air for heating/cooling.

It’s too hot for me I always have to turn the shower down a good bit when I go in.
 
Reuben klang said:
I’ve got a high temp one with a thermal store. Takes the water temp up to 75°c. It’s solely for DHW have air to air for heating/cooling.

It’s too hot for me I always have to turn the shower down a good bit when I go in.
Click to expand...

The efficiency still drops off the hotter you go.

A high temperature heat pump tracks the same efficiency as my ‘low’ temp one. Once you get where mine stops (about 55c flow temp), the difference is the high temp one can continue to get hotter but the efficiency continues to track down and dramatically so at the upper end of its range. There will also be less standing losses from the cylinder itself.

That said, it’s only hot water and not space heating so the cost difference in £ is probably not significant.

Try doing 50c and see how much it costs compared to 55c (and if you have enough hot water of course!). You’ll need to consider legionella at 50c though, I wouldn’t be worried at 55c.
 
b0rn2sk8 said:
The efficiency still drops off the hotter you go.

A high temperature heat pump tracks the same efficiency as my ‘low’ temp one. Once you get where mine stops (about 55c flow temp), the difference is the high temp one can continue to get hotter but the efficiency continues to track down and dramatically so at the upper end of its range. There will also be less standing losses from the cylinder itself.

That said, it’s only hot water and not space heating so the cost difference in £ is probably not significant.

Try doing 50c and see how much it costs compared to 55c (and if you have enough hot water of course!). You’ll need to consider legionella at 50c though, I wouldn’t be worried at 55c.
Click to expand...

I’ll give it a go next week. See how I get on.
 
b0rn2sk8 said:
@glitch did your issues get resolved in the end?
Click to expand...

Apologies for vanishing, had a challenging month since I last posted with some family issues and being stuck in the US with Covid. FWIW there has been radio silence from Aira since they commissioned the system and I have raised an official complaint with MCS and the clock is ticking for them to respond.

Within 24-hours of that being raised, MCS were in contact (I had CC'd them in) and they have asked me to keep them informed about any contact from Aira and will be sending someone out to audit the install and go over everything, with I presume the aim of hammering Aira about their workmanship and doing what they can to assist me with the ongoing issues.

While there have been some improvements to the Aira app in recent weeks and overall the system is working pretty well, all things considered, the lack of support or aftercare from Aira has been shocking. Even worse, unless you call them during business hours, there is absolutely no support if something were to go wrong.

One of the many, many things that have been challenging in the last month were a number of power cuts (thanks, SSEN...) which the Aira system does not take kindly to whatsoever.

Once it comes back online, the remote thermostat will not connect to the system for hours on end, so the system thinks the thermostat is reporting the house is is 0ºC. That kicks everything into overdrive and tries to heat the house up, but as there is no data coming back about the temperature increasing the whole system just goes bonkers. You have to go into the App and manually tell it NOT to heat, which works half the time - if that.

That led to a situation where I was in the US suffering from Covid and stuck in a hotel room, my GF is at home wondering why the house is slowly becoming a sauna and you can't talk to anyone at Aira about this as it's gone 5pm on Friday and nobody will be back to answer the phones (and they rarely do that - typically you have to call over and over and over before anyone picks up) until 9am on a Monday.
 
Reuben klang said:
I’ve got a high temp one with a thermal store. Takes the water temp up to 75°c. It’s solely for DHW have air to air for heating/cooling.

It’s too hot for me I always have to turn the shower down a good bit when I go in.
Click to expand...

Just because you generate at 70C, doesn't mean you should distribute it at that temperature. You want to maximise the system dT and 70C is a fantastic start!

As an example, 500 L of water with a dT of 40K (70 flow, 40 return) gives you a capacity of about 23 kWh. If you halve that, your capacity halves.

Turn your DHW temperature down. Not sure how my two points are connected, but it serves no benefit to flow above the temperature you actually want/need.
 
b0rn2sk8 said:
The efficiency still drops off the hotter you go.

A high temperature heat pump tracks the same efficiency as my ‘low’ temp one. Once you get where mine stops (about 55c flow temp), the difference is the high temp one can continue to get hotter but the efficiency continues to track down and dramatically so at the upper end of its range. There will also be less standing losses from the cylinder itself.

That said, it’s only hot water and not space heating so the cost difference in £ is probably not significant.

Try doing 50c and see how much it costs compared to 55c (and if you have enough hot water of course!). You’ll need to consider legionella at 50c though, I wouldn’t be worried at 55c.
Click to expand...

That's not entirely true. Heat pumps with natural refrigerants e.g., CO2, will flow happily at 70C, but much less happily at 50C.
 
dirtychinchilla said:
That's not entirely true. Heat pumps with natural refrigerants e.g., CO2, will flow happily at 70C, but much less happily at 50C.
Click to expand...
Yeh, but and it’s a big but, we are talking about domestic heat pumps.

CO2 isn’t used because it’s not suited to that application for a number of reasons but principally the efficiency in the temperature ranges/differentials used in domestic heating is not as good as other refrigerants.
 
The_One said:
All you lot heating your hot water tanks to temps in the 40s are risking legionella,

The hw tank should be at 60oc minimum to stop legionella growing in your tank
Click to expand...
Not strictly true, as always, it depends, have a read of this excellent article.

Hot Water Temperature - Scalding and Legionella - HeatGeek

www.heatgeek.com www.heatgeek.com

The author of the article wrote.

For my family home personally, as I turnover around 100% of my stored water each day, I keep my stored water at 45°C and don't do anti legionella cycles.
Click to expand...
 
Last edited:
Afternoon all… quick one.

I have an ASHP. With a buffer, and a secondary circuit pump.

Running 7 rads up stairs and 7 UFH loops downstairs. All open loop.
TRVs all open and all UFH loops open. No secondary control.

Based off my loop lengths, I need 13 l/min to my manifold. But I’m only getting around 8l/min and my living room is colder than the rest of the house.

Based on my circ pump (running variable differential pressure- is that right?) I have a total of 23l/min available.

Should I throttle the lock shields back a little upstairs to divert more flow to the UFH manifold?

I have the installer back in tomorrow I just want to be a little better armed :)
 
Last edited:
I've got a question for the hive mind here.

Do you need a hot water tank with a heat pump or are there any which heat on demand like a combi boiler does?

Reason is that we don't have a tank currently and really don't have anywhere to put one as we designed the house around having a LPG combi, I did a self build 9 years ago so our house is very well insulated but like i say has a combi and normal rads up and downstairs.

Also from looking tanks look to be around the 200 litre mark, is that right? We've got a big free standing bath which i believe is around 220 litres capacity so surely i'd run out of water just filling the bath, what if we wanted a shower or 2 shortly afterwards? Or have i misunderstood and that's not how it works?
 
You must log in or register to reply here.
Back
Top Bottom