Heat loss, and the result

[joth]

4 hours ago, JohnMo said:

Not sure why a mixing valve would not work at the top if a cylinder. It is supposed to be first thing hot water goes through.

 

https://forum.buildhub.org.uk/topic/21490-thermostatic-basin-mixer-taps/

 

Are you sure the issue wasn't the plumber not installing the check valve on the secondary return. As then if the secondary return pump is off the easiest route for the hot to go would be to reverse flow through the secondary loop to the hot water outlet.

If the TMV is right on the cylinder then due to the heat wash it can sit idle at 80°C (if the immersion was on). So in that state it is just wanting to pass only the cold inlet through, meaning you spend a load of wasted water running a bucket of cold through it until it cools down enough to mix and let some of the hot water flow out.

 

Add in the secondary return and things get worse, as the return pump is trying to suck water from a TMV that is set to only allow cold in and not let any hot out of the cylinder, so it's pushing against a dead end and gets no where and makes a racket. This is the main issue: the secondary circuit needs to be a closed circuit, not trying to conditionally mix in water from another source too.

 

Then if you remove the check valve and of course (if the pump is turned off as it's making so much noise), the whole system just slowly draws tepid water the wrong way from the return port when a tap is opened. But that's just adding insult to injury.

 

[dpmiller]

Exactly how close to the cylinder are you talking about- ABOVE the tapping point so you've convective flow into the TMV body?

[Nickfromwales]

13 hours ago, JohnMo said:

Not sure why a mixing valve would not work at the top if a cylinder. It is supposed to be first thing hot water goes through.

 

https://forum.buildhub.org.uk/topic/21490-thermostatic-basin-mixer-taps/

 

Are you sure the issue wasn't the plumber not installing the check valve on the secondary return. As then if the secondary return pump is off the easiest route for the hot to go would be to reverse flow through the secondary loop to the hot water outlet.

I’ve been putting them on the hot outlet for donkeys years, never a single issue. Remember that even if a single check exists, if issues occur, it could be only closing partially and in need of being serviced / replaced. 
Also good to know that there are different types of TMV, some with anti-scald, which will shut off flow in the absence of cold pressure at the TMV. 
Another reason to make sure your water is softened if in a hard water area. All these valves etc need to be able to move freely to function correctly. 
 

14 hours ago, Dave Jones said:

im looking at a 9kw panasonic aquera as running it at 4-6kw is its most efficient apparently.

Just fitted and commissioned one, brilliant machine for the money, and extremely quiet even when I got it to boot up at full wallop to charge the UVC from cold. Cooling is great with them too, as they do that out of the box. 
 

 

[Nickfromwales]

15 hours ago, Big Jimbo said:

My next task will be to try and calculate how much water, and at what temp i will require to store it at, in order to provide enough to run 4 showers at the same time. My thoughts are that, (and i'm not saying i'm right) I don't see the point of storing hot water at much higher temp than i actually need it at the outlets, just to blend it down by then adding cold water. Again with my badly educated mind my thoughts are that the lower temp i store the water at, then the larger the tank will need to be ?

Your problem here will be sustaining pressure / flow for the cold supply on the balanced feed at the UVC control group. You will defo need to design for this from the outset, with much larger primary cold pipe work and an accumulator. 

[Big Jimbo]

Thanks for messing up my head this early in the morning @Nickfromwales What part of badly educated did you not read ? Like i understand anything you just said. 

[Big Jimbo]

I do intend getting a larger mains connected. @Nickfromwales Currently looking for somebody to "design" my water system, but despite reaching out to several engineers, i'm struggling to find someone. 

[Big Jimbo]

I think i get what @Nickfromwales is saying. If say i want to run 4 showers at the same time (3 x 8 and 1 x 12 litres)  that is a total of 36L. That is a lot of water being delivered at the same time, and so will need 36L of being delivered into the system behind it, in order to push it through. Sounds like a problem. 

[joth]

35 minutes ago, Nickfromwales said:

I’ve been putting them on the hot outlet for donkeys years, never a single issue.

Yeah my plumber went away thinking it was working perfectly too. It was only after a couple of days of occasionally having to run off a shedload of cold water  when I opened a hot tap, that I worked out what was up.

 

Fundamentally putting a TMV inside a secondary return circuit is bad design, as you're trying to mix in additional water with no where for it to go to. Regardless how far it is from the UVC,  when sufficiently hot water hits the TMV it will shut off the hot supply and block the pump until the TMV cools again. Possibly resulting in the user having to draw a slug of cold through it to achieve that. So It will perform erratically for the user but very hard for them to recreate the issue for anyone to diagnose, so very possible that the designer/installer would ever know what they did wrong. 

 

(The MIs on my TMV also say it should be located as near the appliance as possible, but that's more that anti-legionnaire police wanting DHW distro at >60° than anything to do with correct function)

 

 

Edited September 15, 2023 by joth

[Big Jimbo]

So with 4 showers, i am going to be looking for a peak demand of 40L per min. Oh, for a decent water engineer. Going to reach out to another One today.

[JohnMo]

Would think you need to know some basic info first, if you have water available.

 

The static and dynamic pressure and flow rate available.

 

Here is a snippet from a a Gledhill cylinder installer manual, let's you know about flow and pressure.

 

 

[ReedRichards]

I thought the correct way to plumb the TMV was to run a loop of pipe down from the top of the cylinder then position the TMV at the bottom.  Hot water from the cylinder can rise up to the top of the loop but for heat to travel down to the TMV it has to work against convection so the TMV stays suitably cool and lives longer.  I cannot remember the exact length of pipe you can use for the loop but you should be able to look it up.    

[ReedRichards]

3 hours ago, joth said:

Fundamentally putting a TMV inside a secondary return circuit is bad design, as you're trying to mix in additional water with no where for it to go to.

 

There is a rather complicated plumbing arrangement you can use to fix this (see figure 4 https://www.hpacmag.com/features/recirculating-domestic-hot-water-system/ .  In the North America you can buy this as a single integrated unit but they're not available here for any reasonable price.  

[Dave Jones]

3 hours ago, Big Jimbo said:

So with 4 showers, i am going to be looking for a peak demand of 40L per min. Oh, for a decent water engineer. Going to reach out to another One today.

 

same, don't forget to add dishwasher, sink and a toilet being flushed to get worse case.

 

I'm doing a min of 3 cylinders (will keep adding them until we dont run out of hot water) and a buffer. Making sure the plumber runs separate runs to every bathroom etc.

 

 

[JohnMo]

30 minutes ago, ReedRichards said:

 

There is a rather complicated plumbing arrangement you can use to fix this (see figure 4 https://www.hpacmag.com/features/recirculating-domestic-hot-water-system/ .  In the North America you can buy this as a single integrated unit but they're not available here for any reasonable price.  

Every day a learning day. So had a dig round the internet to find a drawing of the layout in fig. 4 more applicable to a UK cylinder with a dedicated recirculation loop taping point. See below. The bypass and return valve would be a globe valve or similar to allow accurate and repeated flow control.

 

This setup should allow a continuous flow of water through the cold port of the mixing valve

 

[ReedRichards]

It was in 2020 that I was looking at this.  After wracking my brains for a bit I remembered that it's ESBE who do the most integrated unit and you can now buy one on eBay for a much more reasonable price than I could find then.  Here are some details: https://esbe.eu/group/products/thermostatic-units/vtr300-vtr500 .  Oh, here's a nice little video: 

 

 

Edited September 15, 2023 by ReedRichards

[SteamyTea]

7 hours ago, Big Jimbo said:

So with 4 showers, i am going to be looking for a peak demand of 40L per min. Oh, for a decent water engineer. Going to reach out to another One today.

You could fit a couple of supplementary inline water heaters, say one on the least used shower and one on the most used shower.

Might be cheaper than plumbing in an extra cylinder.

[JohnMo]

7 hours ago, Big Jimbo said:

So with 4 showers, i am going to be looking for a peak demand of 40L per min. Oh, for a decent water engineer. Going to reach out to another One today.

 

4 hours ago, Dave Jones said:

 

same, don't forget to add dishwasher, sink and a toilet being flushed to get worse case.

 

I'm doing a min of 3 cylinders (will keep adding them until we dont run out of hot water) and a buffer. Making sure the plumber runs separate runs to every bathroom etc.

 

 

People with big houses and loads of showers, once you get the water supply issues sorted, you may need to start looking for a cleaner to keep all those bathrooms clean.

[Big Jimbo]

Least of my problems @JohnMo Trying to find a blinking engineer / competent person is hard enough work. Shame we don't have a resident bod on here. I don't mind paying.

[Dave Jones]

1 hour ago, JohnMo said:

 

People with big houses and loads of showers, once you get the water supply issues sorted, you may need to start looking for a cleaner to keep all those bathrooms clean.

 

yep.

[Wil]

1 hour ago, SteamyTea said:

You could fit a couple of supplementary inline water heaters, say one on the least used shower and one on the most used shower.

Might be cheaper than plumbing in an extra cylinder.

Are there any recommendations for an inline that will get a shower going but drop off as the hot water reaches it from the forum hive mind?

 

 

[SteamyTea]

13 minutes ago, Wil said:

Are there any recommendations for an inline

Ask @joe90 what he bought, then sold as it was not needed.

I think his one modulated with regard to inlet temperature.

[JohnMo]

15 minutes ago, Wil said:

Are there any recommendations for an inline that will get a shower going but drop off as the hot water reaches it from the forum hive mind?

 

 

Secondary circulation loop, if you just want to get the shower hotter quicker. No need to add more energy to the system.

[joe90]

29 minutes ago, SteamyTea said:

Ask @joe90 what he bought, then sold as it was not needed.

I think his one modulated with regard to inlet temperature.

Gosh can’t remember what it was called, was going to instal as a back up but decided against it. @Nickfromwales will know 

[SteamyTea]

14 minutes ago, joe90 said:

Gosh can’t remember what it was called

Was it something like this?

https://www.heatershop.co.uk/stiebel-eltron-dce-x-10/12-premium-238159-single-phase-instantaneous-water-heater-4i-technology

[joe90]

17 minutes ago, SteamyTea said:

Was it something like this?

That’s the bugger !!!!!