thermostatic valves

[noelsquibb]

I sorted the TMV on the combi boiler bypass, by fitting an isolator valve on the cold feed, cos it was insisting on adding cold.

Ok, this means someone might have to get a screwdriver out for the summer solar heating ( if it gets the heatstore as hot as some say it will ) but even with the heatstore achieving just under 80c at the top from the WBS, I could regulate the hot flow temp simply by running the bath water faster.

Reckon TMV's have their place but mostly common sense is enough with the certainty that no cold is added.

[EccentricAnomaly]

...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 !!! 

Except that they'll be using less hot water per shower.  As you say, the extra losses are a problem but the basic energy use will be the same.

[Antman]

Agreed Billt

And copper cylinders will tend to inhibit growth of legionella anyway.

I store my DHW at 53 degC - always have done since upgrading the system in the first house from gravity DHW    and I'm still here folks!

I have asked if anyone knows of a legionella case in a domestic property before that is attributed to incorrectly stored DHW. And I'm still awaiting an example.

My view is that all solar systems capable of achieving stored DHW above 60 deg C should have TMV(s) as standard. You never know when a vulnerable visitor will call round. You don't want to be held liable for Great Aunt Maud burning her sensitive skin when washing her hands.....
Arguably 60deg C is too hot anyway.

Antman

[langstroth2]

legionella - even if a cylinder is heated to 60C - very rarely will this mean the whole cylinder reaches 60C, particularly if any sort of draw-off has occurred. So a cylinder could easily be sitting with a bottom layer of water @ 25 - 35 for many hours anyway. This is why I struggle to really see what risk there is in not always heating to 60C, in a domestic setting where the water is regularly changed thru use anyway.

[JohnS]

One of the people at Horne valves used to post on these forums. 

http://www.navitron.org.uk/forum/index.php/topic,5706.0.html

She has not been active since May 2009.

It might be worth emailing Hannah at Horne to see if Horne have anything to say on how to minimise the temperature drop.

John

[Mudman]

But you don't have to lose 12deg through your tmv- as i understand it, the horne valve sold by navitron is much better than normal ones because it only loses 5degrees across it so you can mix 45deg hot with cold and still get your 40deg shower- and they are hardly any more expensive than "normal" ones..

http://www.navitron.org.uk/product_detail.php?proID=370&catID=122

partial quote:

"All mixer valves are NOT equal!

The Horne T15 Mixer valve is particularly suitable for solar use, as it will provide the correct mixed output temperature even with a hot supply temperature some 10-15C LOWER than that required by a standard mixer valve. This makes the valve particularly suitable for solar applications, as it allows the correct output temperature to be achieved even on days when the solar water temperature hasn't reached target temperature. Most mixer valves require 15-20C differential - which means that you need to run your cylinder much hotter to get the same output temperature from your mixer valve.

Minimum Differential between Hot Water Supply and Mixed Output Temperature: 5C"

I'm all for TMVs - when we had a baby last year i fitted a tmv to our bathroom supply just in case- no scalded baby yet (the radio 4 horror story of a baby that fell into a hot filling bath and, although fished out instantly by mother, still died convinced me- it's not uncommon actually) and means we dont' have to warn every visitor that they could be scalded by the landlord's supply of 70 deg hot water.....

[welshboy]

Agreed Billt

And copper cylinders will tend to inhibit growth of legionella anyway.

I store my DHW at 53 degC - always have done since upgrading the system in the first house from gravity DHW    and I'm still here folks!

I have asked if anyone knows of a legionella case in a domestic property before that is attributed to incorrectly stored DHW. And I'm still awaiting an example.

My view is that all solar systems capable of achieving stored DHW above 60 deg C should have TMV(s) as standard. You never know when a vulnerable visitor will call round. You don't want to be held liable for Great Aunt Maud burning her sensitive skin when washing her hands.....
Arguably 60deg C is too hot anyway.

Antman

I bought an unvented cylinder of ebay and the seller turned out to be a legionella consultant and I used the opportunity to explain that I intended using the tank as a preheat cylinder(via heatpump 32c) feeding the supply to the dhw cylinder and ask the legionella implications.
Apparently to catch it you need to breathe it in and the most dangerous would be a fine mist spray so washing hands from a tap seems highly unlikely to cause a problem.

[brackwell]

The official Horne response is indeed 5C which is an improvement but it can be as little as 2.6C depending on temp and pressure. Presumably lower pressure is an advantage.  They put their better performance in this area down to better Mc tolerances (presumably not made in China )

Ken

[martin W]

I suppose the best reply is to have TMV at draw off points only. Could be expensive, but my understanding of the recomendations / legal requirements are store at 60°C, DIstribute at 50°C, use at source (draw off) at 43°C. I think this is hospitols, etc (TMV3 requirements?).

I would think legonnella risk form themal store is pretty low. ONly a small volume of 'potable' water would actually be stored at the breeding temp. To be honest probably not much more than what could be in your water pipes if they are routed near a heaitng source.

I think the main risks are in areas in large buildings where dead legs exist with infrequent draw offs occuring - i.e. it could be months before water is used.

[rob26440]

I suppose the best reply is to have TMV at draw off points only.

Bit of a repeat of my earlier post... I have just one TMV, a Horne25, on the 22mm output from the open vent DHW cylinder for the whole house (except the power showers).  Nice piece of engineering.  The TMV is set to its max and at the farthest away tap (about 20 metres) the hot still reaches 55C and the cylinder is no more than 57/58C.   It has its own cold feed (22mm) from the DCW tank.  It's been in for 2.5 yrs with no complaints from the family.

[brackwell]

I accept the Horne is better than the average but sticking to Mr Average with the cheapo make who has to get the water to 56C + before having a shower at 40C.

If this is done with a thermal store then the hot water temp can never reach the temp of the water in the cylinder as this would require a 100% efficiency.
At this time of the year and at 10L/min this may be 10 C  so the water in the tank now needs to be 66C.  (my relative and a representative of a well known thermal store manufacturer put it at 70C at this time of year )

To get 66C the water entering the tank to provide this energy has to be above this by say another 10C ie 76C    Think of the potential heat losses now!

BUT at 76C if this was achieved with a condensing boiler it will not be condensing so forget the 90% efficiency rollocks.

All this inefficiency to achieve a shower - must be mad.

Ken

[KLD]

Ken,

I don't know where your figures come from. Our Newark thermal store came with a TMV by Watts. I haven't actually measured the temperatures at the pipes, but in winter we run the top half of the store at 55°C. The incomming cold mains is currently at 8°C. The shower incidentally has another TMV fitted. Even with the long pipe run (ca. 15m) from store to shower, the output there is still 40°C.

So, where do you get the idea for these 76°C from?

Klaus

[Greenbeast]

i think he's saying the boiler needs to be at 76 to get the tank to 66, to get through the thermal store DHW pipework at 56 to get through the TMV at 40 for a shower

[KLD]

Ah, understand. So, here we have a great recipe for how to select components to avoid efficiency? 

[wookey]

Why does a TMV have any drop at all? Surely you should get hot water out at same temp as hot water in if it is below the set-point?

KLD - I am interested in your numbers. As we run our hot water system entirly on solar most of the time we worry about temp-drop losses as in winter it often only gets upto 40-something anyway. Which is enough for a shower, but allows no headroom for TMV losses and thermal store HE losses. On the other hand thermal stores are good gear and I'd like to move to one, but want to quantify how much extra non-solar heated that implies (or alternatively how much more infrequently the hot gets hot enough to be useful for showering).

Is your 40C shower with 8C incoming cold and 55C store come from there being a limit of 32C temp raise at given flow-rate, or there being a 15C drop across the HE?