UPDATED: Air Source Heat Pumps/Air Con - Full Info & Guide, is it cheaper to run than mains gas?

Mikeeuropa

lovesgshp: I'm perhaps not explaining my question very well, as we still seem to be disagreeing The mains cold water supply immediately prior to entering the thermal store obviously has insignificantly low levels of legionella in it - otherwise I'd be dead from drinking the cold water out of our taps - it then spends a few seconds whizzing around the heat exchanger coil getting up to (say) 50C and a few more seconds travelling through the pipes to my hot water tap. In that short period of time there's no way the legionella could have multiplied to dangerous levels. And even if it had, sterilising for half an hour next week won't help me when I switch the tap on now.

matelodave: fully understand where you're coming from. If your system has a tank full of warm water sitting in the danger temp zone that will eventually come out the taps then yes, I understand the need to sterilise it.

Without going back through the 60 odd pages of this thread to pick out specific examples, the impression I'd got was that "all" of these ASHP systems had to run this sterilisation routine. And I'd also got the impression that the sterilisation routine, particularly in our winters, was having a significant impact on the efficiency/cost of running these systems. Which lead me to my thought of why don't all ASHP systems use the thermal store route and then surely there would be no need for the sterilisation routine and no reduced efficiencies.

Just to be clear, I don't yet have one of these systems, just trying to do the research before making a decision - ASHP, biomass, or plain old oil.

matelodave

Some of the regulations are probably well over the top for some of the perceived hazards & dangers.
Not all systems have the same problems but it seems once the legislators get their opportunity to get their oar in, then all systems start to get over engineered whether it's really necessary or not.
30 mins a week sterilisation is only 26 hours a year (26-50kw per year I would have thought) so it's not really going to start the next ice age is it, but for some reason it's one aspect of heatpumps that people like to get wound up about

Cardew

Mikeeuropa wrote: »

lovesgshp: I'm perhaps not explaining my question very well, as we still seem to be disagreeing The mains cold water supply immediately prior to entering the thermal store obviously has insignificantly low levels of legionella in it - otherwise I'd be dead from drinking the cold water out of our taps - it then spends a few seconds whizzing around the heat exchanger coil getting up to (say) 50C and a few more seconds travelling through the pipes to my hot water tap. .

You seem to be suggesting that the hot water supplied to your taps was mains cold water a few seconds earlier and has only been heated in the ASHP heat exchanger - rather like a gas combi boiler.

Even gas combi boilers with an output of 30kW to 40kW to heat Domestic Hot Water(DHW) struggle to provide a decent flow at more than 35-40 degrees above the mains input - which can be below 5 degrees in winter.

Even a large ASHP will have a maximum output of 15kW - and considerably less in a cold winter, so never enough to provide 'instant' hot water to taps like a gas combi. So your DHW will have to come from some sort of storage tank.

lovesgshp

Mikeeuropa
Legionella is mainly caused by the bacteria being inhaled in mist particles of water e.g. from showers etc.
I have no intention of arguing, but as I have said before it is a very minor problem with a domestic heat pump system, and you would probably only have to use a system boost every 30 days.
Just to be clear, if your heat store has a 60C constant temp and the cold water is coming in at say 22C, then the bacteria have had the chance to multiply. They need to be at 60C for approx 3 mins to be 90% killed off, so the few seconds through the heat store would be nothing.
In the winter, the risk is far lower, but as here in the summer months, I have ground temps coming in at +20C.
On most systems you should be able to turn the sterilisation off in the winter months if you need to. I do not bother, as it is only about 10 mins.

[Deleted User]

There are also those of us with solar imersion devices.

Our EcoDan no longer does the 60c boost every 14 DHW cycles as the bulk of domestic hot water is heated by the PV.

E.g. Despite being December our hot water tank digital readout is showing 60c

On days where the PV cannot heat the hot water either cos there is no surplus or it's really dull the Ecodan will heat DHW to 50c.

EDIT: Apologies if this not explained very well as brain turned to mush having just bought a new car. Can no longer call myself JeepJunkie

lovesgshp

Not a Jeep? so what is it?

[Deleted User]

lovesgshp wrote: »

Not a Jeep? so what is it?

2010 VW Fox

Much cheaper to run on the daily commute.

Cheers

Mikeeuropa

Cardew wrote: »

You seem to be suggesting that the hot water supplied to your taps was mains cold water a few seconds earlier and has only been heated in the ASHP heat exchanger - rather like a gas combi boiler.

I'm going to give up!!! But not just yet No Cardew I'm not implying it's only been heated by the ASHP heat exchanger. If you look at my original question (or even the post you quote from) I'm talking about hot water coming from/heated by a thermal store, a big tank full of hot water.

Now I give up :rotfl:

Mikeeuropa

lovesgshp wrote: »

Just to be clear, if your heat store has a 60C constant temp and the cold water is coming in at say 22C, then the bacteria have had the chance to multiply. They need to be at 60C for approx 3 mins to be 90% killed off, so the few seconds through the heat store would be nothing.

:rotfl: we're not arguing here Lovesgshp we're just failing to communicate.

Let me try one last time to explain. Lets imagine I have (at some point in the future because I haven't bought it yet) my ASHP sitting outside. It is feeding heat into a thermal store and from what I've seen on here it seems the reasonable compromise between ASHP efficiency and the need for water to feel "hot" that would be say 45C to 50C? When I turn the hot water tap on (or the shower), cold water straight from the mains (with no more legionella in it than my cold drinking water straight from the cold water tap) flows through the heat exchanger in the thermal store (for a few seconds) and comes out at or around the 45-50C mark. This freshly heated water won't have elevated levels of legionella in it because it's not been hot long enough for them to multiply. In that case there's nothing that needs the sterilisation routine.

Does that make sense? I hope I've explained it well enough. Or are you saying that in Italy in summer the water out of the mains may have been warm long enough for there to be significant levels of legionella? I presume that means you can't drink the water out of the tap? But then you wouldn't be able to send it to your shower either - now I'm confused! I don't know what typical temperatures are for mains water in the UK during the summer.

lovesgshp

To be honest, you are trying to complicate things even more with regards to drinking water. Here if we use it from the mains, then it is usually bottled and then refrigerated to about 12C. There are many fresh springs around that have been tapped off where we or the locals fill water bottles up and drink from them, with no known cases of Legionella.
If you install a heat pump then it is up to you as to whether you want the 60C cycle to operate, as it is just a safety factor built into the unit.
As a question, do you have a cold shower in the summer and worry about Legionnela at the time, or is it just about heat pumps now?