Using a PHE instead of a shower mixer valve.

[ringi]

I have been looking at plate heat exchanges to produce DHW from a thermal store for showers and I come up with an ideal that I can’t be the first person to have thought off! (The free Danfoss Hexact software is great for doing the calcs.)

• Have a primary feed and return running at about 55C input (I think I can get it down to 50C).
• Take the feed and return to behind each shower.
• Put a plate heat exchange in to heat to shower water up to about a max of 45C
• DO NOT USE A SHOWER MIXER VALUE
• Control the shower temperature by modulating the primary flow though the PHE using a something like a Danfoss RAVK with the knob in the shower cubical.

The main advantage is that the return temperature in the primary can be well below 30c even using a basic PHE, so letting the boiler run condensing all the time. Also less pipework and pumps are needed then separate heating and DHW loops.

The problems I have are.

RAVK don’t seem to have a large enough temperature range, to allow from a cold shower to a hot shower without a shower mixer. I don’t wish to use a shower mixer as I would get a lower return temperate to the boiler and have to have the primary hotter.

How do seal the RAVK knob as it passes into the shower cubical and make it look nice.

Will the control of the shower temperature be good enough? I will be using “shower heat recover” units, so the incoming “cold” feed will start off at a normal 10c but be preheated to about 25c once the shower is running.

Thoughts please….

Can I buy this off the shelf, e.g is someone selling it as a packaged solution?

Where can I buy plate heat exchanges and RAVKs from in the UK for reasonable prices?

 

[stoker122]

So you would circulate water from the thermal store around the phe?
Pump, electrics, pipework, phe, ravk and shower slider kit or head.
It's gonna cost a bit to install.
Also the water in a thermal store has to be very hot to provide heat transfer so your boiler would still work the same as it is now, on maximum temp.
Sounds like a lot of hassle, you can get a thermostatic shower for £150.

 

[ringi]

I can get 45c output from a cold input of 5c with circulating water from the thermal store at 50c. PHE are a lot better than tank coils! I don’t need the DWH to be at a high temperature, if I generate it at the point of use.

As to the costs of pump, pipe work etc, it does not add much to the system cost as they are needed for the CH anyway. I also save the cost of the DHW pipe work and the pump on the DHW return pipe.

I am looking at doing this for 5 showers, there is not a cheap way to get hot water at that scale, it is also hard to get the best out of “shower heats recover” units with central hot water production and more then 1 shower.

 

[Mike Jackson]

To prevent bacterial contamination the water needs to be stored at 60C and mixed with water of 20C or less at the point of use. This is especially important with showering as legionella is spread by droplet inhalation.

 

[AWheating]

your getting 45 from a 50 store temp? seems good to me,cant see that your going to get much more from that?

and agree with mike above, normally why you have to have mixers, blending valves at point of use.

 

[SimonG]

Lack of control and safety issues spring to mind. Decent mixers stop on losing cold water. Very complicated way of doing something that can be done far easier. It's like re-inventing the wheel, but putting corners on it.

 

[markfxy]

windup

 

[Roger Welton]

A range already available

UK Exchangers Ltd - Packaged Plate Heat Exchangers

You may need a bigger boiler though to keep up

 

[Gray0689]

I have been looking at plate heat exchanges to produce DHW from a thermal store for showers and I come up with an ideal that I can’t be the first person to have thought off! (The free Danfoss Hexact software is great for doing the calcs.)

• Have a primary feed and return running at about 55C input (I think I can get it down to 50C).
• Take the feed and return to behind each shower.
• Put a plate heat exchange in to heat to shower water up to about a max of 45C
• DO NOT USE A SHOWER MIXER VALUE
• Control the shower temperature by modulating the primary flow though the PHE using a something like a Danfoss RAVK with the knob in the shower cubical.

The main advantage is that the return temperature in the primary can be well below 30c even using a basic PHE, so letting the boiler run condensing all the time. Also less pipework and pumps are needed then separate heating and DHW loops.

The problems I have are.

RAVK don’t seem to have a large enough temperature range, to allow from a cold shower to a hot shower without a shower mixer. I don’t wish to use a shower mixer as I would get a lower return temperate to the boiler and have to have the primary hotter.

How do seal the RAVK knob as it passes into the shower cubical and make it look nice.

Will the control of the shower temperature be good enough? I will be using “shower heat recover” units, so the incoming “cold” feed will start off at a normal 10c but be preheated to about 25c once the shower is running.

Thoughts please….

Can I buy this off the shelf, e.g is someone selling it as a packaged solution?

Where can I buy plate heat exchanges and RAVKs from in the UK for reasonable prices?

You ever heard the term over engineering

 

[stoker122]

If the ch is coming off of the thermal store, you're gonna need more than 50 degrees.
How are you going to heat the phe when the heating is off?
Is this for a commercial use with the public involved? If so I wouldn't want to risk injury through using a non approved system.

 

[Dotty]

You're right about one thing, you're not the first person to think of it, why do you think it's not on the market already.

Be quicker, cheaper and easier to go for an off the shelf method.

Sometimes you have to accept your breakthrough and revolutionary ideas are somewhat Heath Robinson....

 

[jam1979]

ringi u shure u havent got that idea off youtube off a scottish guy called dick puller

 

[AWheating]

dick puller........... i think i know her, well she said she was a she................ off to the doctors uke: