ASHP any good for hot water

[Rob55]

Can an ASHP supply hot water for showers and baths? Can ASHP heat the water quickly enough or do you need to have a bigger cylinder to store the water in?

I also see some ASHP’s advertised with a hot water cylinder built in, surely this would be very inefficient as the cylinder and pipe work would be outside in the cold, or is there another reason for it?

[scottishjohn]

 no it cannot be used like a combi boiler

yes you do need a cylinder if using ashp for water heating 

 bigger cylinder -- thats a relative term --bigger than what ?

Edited October 6, 2019 by scottishjohn

[Rob55]

27 minutes ago, scottishjohn said:

 no it cannot be used like a combi boiler

yes you do need a cylinder if using ashp for water heating 

 bigger cylinder -- thats a relative term --bigger than what ?

Bigger than the equivalent size of cylinder that would be used with an oil boiler

[Rob55]

Also is it possible to have mains pressure when taking a shower, or do you need a pump to work in conjunction with a hot water cylinder?

Edited October 6, 2019 by Rob55

[SteamyTea]

You can have either depending on the type of 'cylinder'

There is a fair amount about thermal stores, ASHPs and showers on here.  Try the search function.

It really comes down to the terminology used, it can be a bit confusing.

 

Edited October 7, 2019 by SteamyTea

[Conor]

ASHPs heat water to a lower temperature (50c ish) than a boiler (65c) so you need a larger volume to deliver the same amount of hot water as there is less blending with cold at the outlet. Depends on how many of you are in the Josue and how much hot water you use. But you'll probably need something in the 200-300l range.

[ProDave]

No problem with an ASHP doing hot water if you think about it carefully.

 

You need an unvented cylinder (NOT a thermal store) and choose one with the high capacity heat pump input coil.

 

We store hot water at 48 degrees. that was found by experiment to be as hot as I could possibly hold my hand under without undue pain. I see no point having hot water any hotter than that and the lower temperature you heat it, the easier it is for the heat pump.

 

Because the hot water is less hot than it would be from say a gas boiler, you will dilute it with less cold to get your final temperature, so you will need a bigger tank.  We have a 300L tank and that is just about okay for 3 of us.

 

Our heat pump is only 5KW so the hot water will take a lot longer to re heat after using some than it would from your average gas boiler.

[joe90]

Like @ProDave above we have an ASHP and 300ltre DHW tank and it does us plus a couple of guests just fine. We have a couple of immersions in the tank in case of ASHP failure/downtime or loads of guests but not needed yet.

[scottishjohn]

there are simple solutions already made by mitsubishi and others where the heat pump for UFh and the tank  for DHW and all pumps etc are supplied as a complete package

 will probably be more expensive than buying it in bits --but If t you are not really up to speed with these things its a simple solution .

i went that way when going ASHP +rhi --works great and if a problem only one man to speak to 

 all the pumps  3 of them  and controls are mounted on the pre plumbed cylinder --so connections to use are very simple

wi-fi control etc etc 

Edited October 7, 2019 by scottishjohn

[MikeGrahamT21]

Just a note to people wanting to store/use water at lower temperatures...

 

Some bacteria will not be destroyed at these lower temperatures, pseudomonas being one of them, so if possible (and I dont know the technical side of ASHP type systems) design in perhaps another method of heating the water to a much higher temperature (immersion heater perhaps), so that you can run a high temp cycle one a week to stop bacteria from colonising.

 

Pseudomonas also likes underfloor heating loops for the same reason, low temps and plastic pipe, perfect environment, so ensure with UFH that you put the correct amount of water treatment in, as high temp cycles with this aren't possible.

 

And please take this seriously for yours and your families sake, I've been on the sharp end of Pseudomonas, its not a nice bug and it will and does kill people.

[joe90]

We have an immersion for anti legionella protection but after reading here that there has not been a single case of domestic problems with this I have not bothered to wire it up. I believe the problem comes from stagnant water in shower heads that are not used fir a period of time. 

 

Edit to add,- As i had not heard of pseudomanas I had to look it up and found this,

 

Pseudomonas is a germ found in the environment. It can occur in moist areas such as sinks or baths. It rarely causes illness outside a hospital or healthcare setting.

 

Edited October 7, 2019 by joe90

[ProDave]

I have no deliberate anti bacterial cycle.  (mostly) in the summer surplus solar PV heats the HW tank via the immersion heater and on a good day it approaches 70 degrees before the immersion heater thermostat opens. But that is not going to happen in the winter.

 

We discussed this at the time, and the conclusion was our mains water originates from a cold mountain loch where the chance of any bacteria surviving in the first place is low.  It then goes through a treatment plant that included a microfilter.  So we can be pretty sure there is no bacteria in the water when it arrives.  The hot water tank is unvented, so there is no route for contamination to enter.  So the consensus on the forum at the time is any bacterial risk from the stored hot water in incredably small.

[Jeremy Harris]

We've discussed the possible health risks here before, but the bottom line is that in a closed system, supplied by mains water, there is zero risk of any bugs growing in the hot water system, as far as the inlet to any taps, mixers etc.  Bugs have to have a way to get in in order to start multiplying, and that means the water supply either being compromised somewhere, or being open to the air, say from a break tank, cold water tank etc.

 

There is a small risk from standing water left in the pipes feeding a shower head, as that water is exposed to air and sitting at room temperature, so it's a good idea to not let a shower sit unused for long periods of time.  The more frequently a shower is used, the less chance there is of bugs growing in that water column.  Even then, the risk is low, but exacerbated by the water being sprayed into the air in the first second or so that the shower is running, so increasing the risk that any bugs will be breathed in.  If someone has a compromised immune system, or is suffering from lung disease, then the risk from using a shower for the first time in a week or so could be minimised by placing the shower head in a container of water when first turning it on, perhaps.    In reality I suspect the risk is very low, and not something that's likely to ever be a problem for a shower that's in regular use.

 

 

[MikeGrahamT21]

Just bear it in mind when doing anything with lower temperatures than normal. MVHR ducting is another place it can lurk.

 

Obviously this is more of a worry for the immune compromised person, but even normal people can get ill from it, and it can happen anywhere not just in a hospital environment, this is just more likely as people are ill and their immune systems compromised.

[MikeGrahamT21]

3 minutes ago, JSHarris said:

We've discussed the possible health risks here before, but the bottom line is that in a closed system, supplied by mains water, there is zero risk of any bugs growing in the hot water system, as far as the inlet to any taps, mixers etc.  Bugs have to have a way to get in in order to start multiplying, and that means the water supply either being compromised somewhere, or being open to the air, say from a break tank, cold water tank etc.

 

There is a small risk from standing water left in the pipes feeding a shower head, as that water is exposed to air and sitting at room temperature, so it's a good idea to not let a shower sit unused for long periods of time.  The more frequently a shower is used, the less chance there is of bugs growing in that water column.  Even then, the risk is low, but exacerbated by the water being sprayed into the air in the first second or so that the shower is running, so increasing the risk that any bugs will be breathed in.  If someone has a compromised immune system, or is suffering from lung disease, then the risk from using a shower for the first time in a week or so could be minimised by placing the shower head in a container of water when first turning it on, perhaps.    In reality I suspect the risk is very low, and not something that's likely to ever be a problem for a shower that's in regular use.

 

 

Unless its been filtered with UV light, mains water has every chance of containing a tiny particle of bacteria, all it takes is one to start a colony. I'm not trying to scare monger here, just speaking from experience and advising care

[joe90]

2 minutes ago, MikeGrahamT21 said:

mains water has every chance of containing a tiny particle of bacteria,

 

Is this not why it’s treated with chlorine? Saying that I know there are no guarantees in life, shit happens sometimes. (Sorry that was not meant to be a pun ?).

[Jeremy Harris]

1 minute ago, joe90 said:

 

Is this not why it’s treated with chlorine? Saying that I know there are no guarantees in life, shit happens sometimes. (Sorry that was not meant to be a pun ?).

 

 

Yes, and that's precisely why chlorine is used, as it provides very good residual disinfection in all the supply pipes.  It only ceases to have any effect when the water is exposed to air, hence the problem with contamination getting in through break tanks etc.

[MikeGrahamT21]

10 minutes ago, joe90 said:

 

Is this not why it’s treated with chlorine? Saying that I know there are no guarantees in life, shit happens sometimes. (Sorry that was not meant to be a pun ?).

It is yes, but pseudomonas can tolerate chlorine to a certain extent, heat or ozone is the only thing that is 100% guaranteed to kill it. It lives in drains and damp soil, so you can imagine what it has to put up with, it coats itself in something called a biofilm which prevents all the things which normally kill bacteria from working. As an aside, it also has the ability to evolve, and has become one of the most resistant bugs to antibiotics.

 

Have a look at this, as pseudomonas isn't the only bacteria with a biofilm: https://www.ncbi.nlm.nih.gov/pubmed/27146505

 

Careful design and consideration is all thats needed. Having spent the last 18 months reading intensly about this particular bug, i'm probably more aware than others at just how bad it can be, so wanting to put all that knowledge to some use.

Edited October 7, 2019 by MikeGrahamT21

[Jeremy Harris]

21 minutes ago, MikeGrahamT21 said:

Unless its been filtered with UV light, mains water has every chance of containing a tiny particle of bacteria, all it takes is one to start a colony. I'm not trying to scare monger here, just speaking from experience and advising care

 

 

UV is far less reliable than chlorine disinfection used by the water companies, both because it's not 100% effective (some bugs might not get dosed enough to kill/deactivate them) and also because it provides zero residual disinfection.  A UV unit must never be used in front of storage  vessels for this reason, but always immediately before the supply to all outlets.  Residual disinfection is a really big advantage of chlorination, as the effectiveness of it is, like all other disinfection methods, heavily dependent on exposure time (one reason why ozone isn't as effective for treating water before storage/distribution).

 

14 minutes ago, MikeGrahamT21 said:

It is yes, but pseudomonas can tolerate chlorine to a certain extent, heat or ozone is the only thing that is 100% guaranteed to kill it. It lives in drains and damp soil, so you can imagine what it has to put up with, it coats itself in something called a biofilm which prevents all the things which normally kill bacteria from working. As an aside, it also has the ability to evolve, and has become one of the most resistant bugs to antibiotics.

 

Have a look at this, as pseudomonas isn't the only bacteria with a biofilm: https://www.ncbi.nlm.nih.gov/pubmed/27146505

 

 

The clinical evidence shows that infections from domestic water supplies are very low.  The data is collected monthly and published here: https://www.gov.uk/government/statistics/p-aeruginosa-bacteraemia-monthly-data-by-location-of-onset

 

Looking at the last annual data set the incidence of "community onset" infections (which includes care homes, as well as domestic locations) is pretty low, and almost all can be traced to a setting other than a domestic dwelling.  I can find no evidence that domestic hot water systems are a significant risk factor, especially not for otherwise healthy individuals.

[MikeGrahamT21]

I'm just giving information from a medical perspective based on real research which is happening and experience.

 

There is absolutely no significant risk to a healthy individual I totally agree, but can you guarantee thats how you are going to be your entire life?

[joe90]

Just now, MikeGrahamT21 said:

I'm just giving information from a medical perspective based on real research which is happening and experience.

 

There is absolutely no significant risk to a healthy individual I totally agree, but can you guarantee thats how you are going to be your entire life?

 

I agree but life is all about risk evaluation, I would suggest that if it was deemed a risk to the general public it would fall under building regs. Our neighbour has a diminished immune system because of an illness and she takes more precautions than most (won’t go near our chickens or touch our dog).

[PeterW]

I’m looking at using an ozone generator for a rainwater tank but struggling because the air pumps don’t seem powerful enough to reach 8-900mm depth needed to get the air stones into the bottom of the tanks. Other thought is to change the design and allow it to recirculate between the tanks and put an ozone Venturi injection in the recirculating loop. 

[Ed Davies]

1 hour ago, MikeGrahamT21 said:

Just bear it in mind when doing anything with lower temperatures than normal.

 

My emphasis. Probably better said as “storing significant quantities” or something like that. Lower temperature water isn't a problem so long as the stored water is changed regularly and very thoroughly so the wee beasties don't have time to breed.

 

This, to me, is a key attraction of the Sunamp. The quantity of water in the heat exchanger is very small and changed every time any meaningful amount of water is drawn off. Water-based thermal stores can have the same benefits but have the disadvantage of the temperature dropping off as heat is drawn out. A UVC, on the other hand, could easily have odd corners where the water doesn't change often which is fine if the whole tank is pasteurised regularly but a bit ickey if it could go months between high-temperature periods.

[Adam2]

If the main risk is water in shower heads due to contamination through air exposure then I don't see how heating the tank periodically will make any difference at all to mitigate that risk as by the time the "fresh" hot water arrives at the shower head the bacteria is already in your eyes, ears and nose. If this is correct then hard to see any point in heating the tank to 65.

[scottishjohn]

the mitsubishi system i has and anti  baceriaa function built in and every now and then it lifts water temp high to kill anything without nay input from me