My ASHP Journey in Bonnie Scotland.

matelodave

As I've said on previous occasions we only heat the tank once a day for an hour or so to 45 degrees which gives us as much hot water as we need.

However its considered that 45 degrees is insufficient to kill off legionella so heatpumps, which can usually only manage to heat hot water to around 50-55 degrees, have a sterilisation cycle which boosts the hot water temperature to 60 degrees or more by using the immersion or boost heater and hold it there for half an hour or so. 

Most machines allow you to choose when you want this to happen, how often and what temperature. Mine only allows a once a week cycle although I can choose when, how long  and how hot whereas I know some units allow you to extend the periods between cycles to more than a week.

IMO having a non-vented tank which is fed directly from the mains which is already sterilised with chlorine (smells like a swimming pool some days) shouldn't really need a weekly sterilisation.  Unlike an open vented hot water tank filled from a cistern sitting in the loft, especially in the summer where water can get warm enough to gently ferment all sorts of stuff.

cannugec5

ahh, now I get it. If SOME units permit less frequent than weekly legionella cycles then one would presume that to be safe. 

I know mine is set for a weekly boost. 

Having previously worked in hospitals we were paranoid about legionnaires disease and any unused rooms with taps in had to be flushed through and recorded weekly. ( Swan neck taps with sitting water in them). 

I hadn’t considered the lack of a tank in the attic. On our old one, recently removed, the lid didn’t even fit! Goodness knows what was in there…

So unvented= sealed, so the only water flowing in is drinkable mains water. 

Thank you for taking the time to explain it to me. 

QrizB

matelodave said:

Unlike an open vented hot water tank filled from a cistern sitting in the loft, especially in the summer where water can get warm enough to gently ferment all sorts of stuff.

In my parents' old house, bats would occasionally fall into the loft tank and drown. (Or maybe they roosted above it and just died of old age, then fell in. Whatever.)
The first you'd know is when you got clumps of fur coming out through the hot taps ...

Strummer22

QrizB said:

The first you'd know is when you got clumps of fur coming out through the hot taps ...

Delightful! 

Our heat pump also only has the option of a weekly boost - but has the option to turn it on or off. Weekly seems overkill so I run it only every couple of months. We're not dead yet.

matelodave

you might find this interesting, poor heatpump intstallation and badly set controls- https://youtu.be/H0jeVhx0WsQ

markin

The best time to heat water is the warmest part of the day around 12-2pm

matt_drummer

markin said:

The best time to heat water is the warmest part of the day around 12-2pm

For efficiency and in the summer, yes.

In the winter I use E7 and want the heating during the day.

So I heat the water in the afternoon when it's warmest, I am generating from solar panels and have full batteries.

In the winter it is cheaper to use the E7 rate to heat the water saving any solar and battery storage for heating use during the more expensive period.

FreeBear

matelodave said:

As I've said on previous occasions we only heat the tank once a day for an hour or so to 45 degrees which gives us as much hot water as we need.

However its considered that 45 degrees is insufficient to kill off legionella so heatpumps, which can usually only manage to heat hot water to around 50-55 degrees, have a sterilisation cycle which boosts the hot water temperature to 60 degrees or more by using the immersion or boost heater and hold it there for half an hour or so.

Just maintaining a temperature of 55°C for an hour or so is enough to kill most of the bacteria - See attached graph.

Further information can be found here - https://www.heatgeek.com/hot-water-temperature-scalding-and-legionella/

MikeFl

cannugec5 I too have a new (well, April this year) Grant Aerona with that warning label on it. But I also have an installation guide with no installation parameter settings recorded in it, incorrect flow rate set, and no decent handover from the installer ... so the same people who are putting the "do not touch" sticker on the controller basically failing to complete the installation properly by recording the installation settings they used. I suspect I'm not alone in this.

They also left the system with a fixed leaving water temperature, hot water heating up for 3 hours every day, and CH water pressure set to 2.5 bars. This seems common - that ASHPs are being installed and left in a kind of "gas boiler" mode, which isn't the best way to operate them.

I would definitely make a note of the main parameter values, and then change them to suit your needs. I've found DHW on for 1 hour a day fine (3-4 pm) and reduced the temperature from 55C to 45C, with anti legionalla running once a week. I'm starting to adjust the weather compensation as well, but that's more of a long-term plan.

FreeBear

MikeFlcannugec5 I too have a new (well, April this year) Grant Aerona with that warning label on it. But I also have an installation guide with no installation parameter settings recorded in it, incorrect flow rate set, and no decent handover from the installer ... so the same people who are putting the "do not touch" sticker on the controller basically failing to complete the installation properly by recording the installation settings they used. I suspect I'm not alone in this.

Had a new gas boiler installed earlier in the year - Not one parameter was set, and the programmable thermostat wasn't even communicating with the boiler. Didn't help that the thermostat wasn't wired up correctly.

So no, you are not alone in having a misconfigured installation.