thermostatic valves

[brackwell]

Hi All,
It was only a few months ago that this forum brought these things to my attention but now have some doubts about their use within the DHW set up.
Under what circumstances do you LEGALLY have to have them ?  What about with a Thermal Store /wood burner /solar panel / immersion heater ?

The reason i ask is making some enquires of manufacturers of these things they typically cool the hot water down by 12 C  at the tank end and then when it gets to the thermostatic shower there is another min 4 C (although my experience suggests it is more than this ) . They never switch off the cold water completly! This means we are all useing energy to create hot water so that we can add cold.  Is this not madness in the extreme ?  ( probably accounts for one of Martins nuclear power station all by itself ) 
This year i will change my solar pre heater tank to directly feed my shower through a zip heater and then when the solar water is 40 C or above it will be free. Compare this to having to heat your tank to 56 C before you start !

Ken

[CeeBee]

Someone else will have to answer the "LEGALLY" bit, since I'd just be trying to look it up on the web like presumably you are.

But off the top of my head, I don't think there's any legal requirement unless you're in the care home / hospital / school? / etc. area.

I don't have one on the tank output from my own solar thermal system, and indeed it can get very hot in summer (no heat dump either - it seems to be sized about right so that neither are needed). I do have a thermostatic power-shower, but that's more the convenience of it producing water at a reaonable temperature independent (within reason) of the temperature of the hot and cold.

Disadvantage of over-hot water (apart from those you mention): it might degrade any bits of the plumbing susceptible to high temps.
Advantages: you can pack more energy into your storage tank (avoids having larger tank), and there might still be usable warm water at lower levels in the tank after you've drawn off the hottest top layer.

[billt]

The reason i ask is making some enquires of manufacturers of these things they typically cool the hot water down by 12 C  at the tank end and then when it gets to the thermostatic shower there is another min 4 C (although my experience suggests it is more than this ) . They never switch off the cold water completely! This means we are all using energy to create hot water so that we can add cold.  Is this not madness in the extreme ?  ( probably accounts for one of Martins nuclear power station all by itself )

Adding cold water to hot to reduce the temperature does not waste energy. You will be taking less hot water from the store than you would if the store temperature were lower; the energy usage will be the same to all intents and purposes. (There will be a bit of extra loss if your store and pipework is inadequately insulated due to the slightly higher temperature needed, but that should be low with good insulation.)

If your source of heat is mainly a controllable one like a gas or oil boiler with only a small contribution from solar then a thermostatic valve is not needed. If there is a significant contribution from a source which is not very controllable you would be badly advised to not use a thermostatic valve.

For example, we've been using our Rayburn for a few days recently. Although it is reasonably controllable the hot water was still getting to over 85C which is potentially dangerous. We needed to exercise great care when using hot taps. That sort of temperature can easily be reached with hot water provided by a log boiler heated store.

AFAIK CeeBee is right about the legality.

Bill

[Green Transitions]

I would agree with CeeBee as well about where they legally need to be used, pretty much any 'high risk' or 'sensitive' areas, care homes, schools etc. Worth seeking a definitive answer from the WRAS or B regs etc. if in doubt though!

When I took a refresher for unvented systems last year, the instructor told me not to bother updating my WRAS cert yet, as from what he had heard the 'gov were trying to implement legislation to make 'everyone' use thermal mixing valves, at every point of use. Initially just for bathrooms, but eventually every single hot water outlet in the home/office/wherever would need one. An incredible feat to achieve/regulate, but I would not be surprised if they tried. Of course, every thermal mixing valve would need a yearly check! Kaching.

Anyone else heard anything like this? Not really looked into it much since I heard.

[brackwell]

Bill ,
Of course in one sense you are correct in that it allows a small tank at high temp to store the same energy as a larger tank at lower temp. However this assumes you use all the hot water you have produced in quick time otherwise you are in to heat losses.  These heat losses are still significant when everything is super lagged simply because it is a process that is going on 24/7 .  What is the situation when you dont use all the hot water produced (which is virtually always the case for me and wife ) then one is heating water that is never used and a 120l of water at 40 C is as usefull as a tank at 56 C . If after using the same amount of hot water energy in both cases and then nothing happened for 24 hr  the two temps would be virtually identical and therefore no gain was derived from the hotter water. 

The most efficient heating is like a instantaneous shower - heat just enough and use immediately. Hence use solar panel water perhaps not heated quite enough then add a bit more energy instantaneously before use.   Save on all the heat losses of boilers,pipes,pumps,standing losses etc ! job done.

Anyway i will monitor the energy used although i have yet to see a power meter that can handle 9 Kw - any ideas anybody.   At the end of the year i will be able to compare gas usage during the non central heating period so as to remove that variable.

Ken

[daftlad]

Anyway i will monitor the energy used although i have yet to see a power meter that can handle 9 Kw - any ideas anybody.
Ken

A whole house energy monitor, put the sensor around the wire in the fuseboard. Of course if you arn't happy with elastic trickery find someone who is.
Be safe.
ta ta

[odbob]

In all instances, stored domestic hot water should be heated to 60c or thereabouts to kill off most of the nasties that can breed very quickly at lower temperatures (a fact that seems to have been forgotten in certain instances of 'green' philosophy) having heated this water to 60c, then you do what you want with it, in a normal house the occupants would usually know that the water leaves the hot tap at an uncomfortable temperature and so this promotes the use of the plug, a device rarely used these days, but saves much water. The shower outflow is tempered with cold water either as a thermostatic or manual mixer

[rob26440]

I believe there is already legislation in Scotland about the installation of TMVs in new & "reworked" domestic properties (as well as hospitals, care homes, schools, etc.).  I'm seeing them a lot more in England in public places and in shops/stores where they have public use WCs/bathrooms.

I have a Horne25 TMV (which has 28mm fittings) for the whole house (gravity fed - with v. little head to the bathrooms).  It's set to its max, which is about 55C, and I have measured that temp at the furthest tap – once the dead leg has been filled.  So temperature drop is not a problem for me.  The solar panel gets the hot water cylinders (2 of them) into the high 70's during the summer.  Dangerous stuff hot water - especially for the elderly, infirm & children.  I'm all for having TMVs – but not necessarily mandated by draconian legislation that will put people off.

Another reason for using a TMV is to protect the power shower pump.  My Salamander RHP75 is rated at 65C max input.  So there's a 22mm TMV on the hot input to the pump.

[JohnS]

Ken,

Whilst I accept your point about heating water to a higher temperature than might be required causes waste because of higher cooling losses, it is not nearly as bad as you are making out.

In the heating season, any losses and to the heat supply to the house (assuming the HWC is not in a garage or attic).  It is just what would be produced by the boiler for central heating anyway.  It is broadly irrelevant whether the heat is given out immediately or stored in some way, the total amount of heat created is the same, so what is important is how much heat and how efficiently is it produced. 

In the non heating season, the HWC is heated by solar and of course that can go much higher than is needed.  Hence the need for TMVs. 

Perhaps in the shoulder seasons, you have a point, but the requirement to prevent legionellas is more than enough to negate this.

Also, I am quite happy for my shower to run 4 degrees cooler than my kitchen or bath tap and therefore the shower TMV heat loss because of cold feed is necessary and irrelevant.

John

[martin W]

If you already have a TMV type mixer tap shower, just add a TMV at your bath room taps and kitchen sink tap, that way you dont need to worry about any temp drop from the tank.

My thermal store had a TMV, and as long as the store is about say 50°C both my wife and I can shower in the warm so the temp drop is not that much. Shower is tmv mixer type set at about 30-35°C (depending on how cold we are). CUrrently store is about 14°, output from TMV around 13°C, in coming mains cold around 7-8°C, outside air -8 to -2°C.

Obvoiusly not a lot of use at the moment, but solar is pre-heating the cold water by around 3-4°C for my combi-boiler, so saves a bit of gas.

I can't give you temp drops for hotter water (50°C plus on the store), as my temperture sensor system (1-wire), has only been runing a few days.

[dhaslam]

It would be better if thermostatic valves would be efficient enough to work  without having to  have both hot and cold running.     I need to have hot water at 52C  to have 38C  mixed temperature.     The heat pump will only heat water to about 55C  so it usually means using the immersion at least for the second shower.  I have UV on the water inlet  so 55C should be more than adequate.   It does cost quite a bit extra to heat the water a few degrees more than necessary. 

[brackwell]

Martin W and Dhaslam are recognising the problem although shower at 30-35 C !!!

Looking at this from another perspective
In summer the solar panel does the bis and no other heat input but then we get to the stage when the solar manages  say 45 C.  At this temp we can still have jolly fine showers but those with TMV cannot and have to add energy - this just has to be unnecessary waste.  It now enters Winter and the solar is now say managing 20 C (which it did for me before the snow covered the panel last week ).  I now have to enter say 20 C worth of energy to get to 40 C and have a shower. The TMV guys have to add say 36 C worth of energy before they can have a shower - thats double the amount if you include a bit for losses !!!   Looking at it like that how can tmv be anything but a waste - For sure a great health and safety device.  Whats more as soon as one adds powerfull gas heating or immersion heater the stratification in the tank is destroyed has as been investigated by others on this forum. Some would say gas boiler/CH  on = solar is killed.

Ken

[Greenbeast]

put in a manual valve bypass of the tmv?

[odbob]

I keep hearing of stored domestic water temperatures at much lower than 60 deg c, this can lead to bacteril problems, legionella being just one.

[billt]

I keep hearing of stored domestic water temperatures at much lower than 60 deg c, this can lead to bacteril problems, legionella being just one.

That's another issue that's migrated from public areas, where it may be an issue, to private ones, where it is almost certainly not an issue.

The most dangerous contaminants of water supply are things like some varieties of e-coli, which will not be present in a properly functioning public water supply and any that do find their way in should be killed by the residual chlorination.

In the unlikely case of legionella being present in the water supply it is true that the residual chlorination will not kill it and that the easiest way to kill it is to maintain a water temperature of over 60C for a period of time. However, legionella is not a danger when ingested, it is only dangerous when inhaled in an aerosol, and then it is only a serious issue to those with a compromised immune system.

Most cases of legionella are not caused by water supply but things like improperly maintained air conditioning cooling systems spraying contaminated water into the air.

It makes sense to ensure that water supplies in public institutions, like hospitals, are heat treated so that potentially vulnerable patients aren't exposed. The combination of a low risk of legionella contamination in the first place, a low risk of exposure by aerosol and the lack of danger to most people make it an insignificant risk in the private area.

There is no reason not to heat water to 60C if you want to but making alarmist statements like the above just adds unnecessarily to the general air of paranoia that seems to prevail these days.