DAFI 400v Water Heater protection

[Marty21]

@flameport - well I'm grateful to you and everyone else who has put a view forward - it's been really, really helpful. I'm sure I can't be the only person who has to think through these issues. Maybe some of the wider points raised will help others, too.

If it's a total fail with the Dafi, I'll come back and tell you. But at the moment, the capital (installation) cost and running costs appear very favourable compared with all the other options, even if we end up putting three 11kW Dafi heaters in.

 

[oldbutnotdead]

I'll certainly be interested to hear how well the 11kw jobbies work- I don't have the luxury of 3 phase available but am looking at a similar sketch- using an unvented 11kw instant heater to service utility room and shower/toilet. I know electric showers are deeply average in performance but (at the moment) the primary heat source in the house is the woodburner so for the summer when I can't be bothered to light a fire and the heat store is depleted due to British summer and no fire, the electric jobbie will give me an average shower but (hopefully) an excellent utility room sink and washbasin feed. Just not all at the same time

 

[ericmark]

My answer was with the idea of DIY, I had not realised this is a commercial premises. The pros and cons of intent to stored hot water is always hard to work out, as there are so many often hidden problems until it comes to connecting them up.

I had a problem office block, the single phase supply was too much with people replacing the storage heaters with fan heater, I was running at around 120 amp with 100 amp fuses on that phase, so when it was proposed to fit showers for the workers I put forward the idea of a oil or gas fired boiler which would both reduce the load in offices and supply the shower block with hot water.

However the manager responsible seems to have a hearing problem, he installed 4 electric showers then said can you connect them up, and thought I was being unreasonable when I said no.

I think you need to have professional advice before going ahead, the amount of heat lost with a hot water storage vessel is a lot less today than it was 20 years ago, we have worked out how it insulate things today.

 

[ban-all-sheds]

the electric jobbie will give me an average shower but (hopefully) an excellent utility room sink and washbasin feed

How do you intend to regulate the temperature of the shower water, and what fast-acting anti-scald protection will you put in?

If this is a simple instant water heater and not an actual shower you might be about to make something dangerous.

 

[JohnW2]

How do you intend to regulate the temperature of the shower water, and what fast-acting anti-scald protection will you put in? ... If this is a simple instant water heater and not an actual shower you might be about to make something dangerous.

I initially wondered, too, but came to presume that he is probably intending to feed a thermostatic shower mixer from the instant water heater, just as one would do with a combi-boiler (which, after all, is just a differently-fuelled version of an electric instant water heater).

Kind Regards, John

 

[oldbutnotdead]

Morning all & ta for replies- as JohnW2 surmised, the plan is to use a standard thermostatic shower mixer head for the shower bit and set the output temperature of the jobbie to 50 degrees or so (so scald risk from the taps is the same as with any other hot water source). It won't surprise me in the slightest if the performance is uninspiring but the cost isn't massive and the pipework will take about 15 minutes to rearrange for the different setup so it'll be (I think) a worthwhile experiment. It's not high on the list of jobs so I'll see how the OP gets on...

 

[ban-all-sheds]

That won't work. A thermostatic shower mixer can't be attached to the output of an instant heater.

When the temperature of the mixer output rises too high it will restrict the hot flow to compensate.

Think about what happens with an instant heater if you restrict the flow through it....

And vice-versa - if you want the shower temperature hotter, the mixer will increase the hot flow. When you increase the flow through the heater, the temperature will fall.

You'll almost certainly find that the maker of the heater advises against what you plan to do.

A combi boiler, note, has integral thermostatic control - it doesn't heat the water to the max until it overheats and shuts down.

 

[JohnW2]

That won't work. A thermostatic shower mixer can't be attached to the output of an instant heater.

No? I think a goof few instant water heaters are more like combi boilers than you seem to think.

A combi boiler, note, has integral thermostatic control - it doesn't heat the water to the max until it overheats and shuts down.

What do you mean by 'the max'? If you turned on just slightly a tap connected to an instant heater, would you expect the water to boil, or what?

You'll almost certainly find that the maker of the heater advises against what you plan to do.

From one of the first hits I got when I Googled "electric instant water heater". There are countless similar ....

Kind Regards, John

 

[oldbutnotdead]

No? I think a goof few instant water heaters are more like combi boilers than you seem to think.
What do you mean by 'the max'? If you turned on just slightly a tap connected to an instant heater, would you expect the water to boil, or what?
From one of the first hits I got when I Googled "electric instant water heater". There are countless similar ....


Kind Regards, John

Yeah, the existence of these things surprised me too, I've been used to the traditional type (open vent tank or no tank) so was very pleased (actually a bit narked because I'd just installed an electric shower in a location which would have been ideal for one of these). Ho hum- but lesson learned, just because it didn't exist doesn't mean it'll never exist!

 

[Marty21]

Dafi's own literature shows one of their heaters connected to a shower: http://www.dafi-water-heater.com/en/content/14-manual

 

[ban-all-sheds]

A shower using what sort of mixer?

 

[JohnW2]

A shower using what sort of mixer?

Hopefully thermostatic. What else did you have in mind?

Kind Regards, John

 

[ban-all-sheds]

It's not so much what I had in mind, as what you had in mind, or what the maker has in mind when he says "shower". He might mean a manual mixer and you might be assuming he must mean a thermostatic one.

What type of showers can be supplied? - Redring only recommend their shower mixer kit but some client's have had varied success with other manual mixer showers (thermostatic mixers are definitely out).


Q: i have just bought a Redring Power Stream 10.8kw heater unit and a Atmos Fusion Thermostatic Concentric Mixer Valve shower unit and have noticed that in the redring instructions it says 'In order for the Powerstream to function correctly, the "Redring Mixer Kit" must be used.
Is this a case of Redring wanting to keep everything in house or will the heater unit work ok with the thermostic mixer shower i've already bought?
A: The redring shower valves are a very basic shower valve that lets all of the hot water capacity through and you control the temperature by adding small amounts of cold water.


//www.diynot.com/diy/threads/instant-water-heater-with-thermostatic-mixer-shower.353520/


The unit MUST NOT be fitted to any type of THERMOSTATIC mixer valve or tap. .... If the Powerstream-Eco is connected to a mixer tap then only NON-Thermostatic types should be used (water mixes at the outlet pipe only).


Hyco used to say "Do not fit a thermostatic mixing valve with the inline. Unpredictable performance will result" but I can't find that now.​

Maybe other makers of instant heaters have done theirs differently and thermostatic mixers can be used.

Maybe, as oldbutnotdead says, things change, and what was not available a few years ago is now.

Maybe the maker of the instant heater someone chooses should be explicitly asked to specify what type(s) of shower mixer can be used.

And maybe the OP should wonder if all this bother is worth it to get a heater which is only 2% more powerful than an electric shower...

 

[JohnW2]

It's not so much what I had in mind, as what you had in mind, or what the maker has in mind when he says "shower". He might mean a manual mixer and you might be assuming he must mean a thermostatic one.
.... Redring only recommend their shower mixer kit but some client's have had varied success with other manual mixer showers (thermostatic mixers are definitely out). ...........
The redring shower valves are a very basic shower valve that lets all of the hot water capacity through and you control the temperature by adding small amounts of cold water.
The unit MUST NOT be fitted to any type of THERMOSTATIC mixer valve or tap. .... If the Powerstream-Eco is connected to a mixer tap then only NON-Thermostatic types should be used (water mixes at the outlet pipe only).

I can but presume that these statements must all relate to the types of instant water heater (like 'over-sink' ones) which have to have an 'open' outlet and therefore cannot safely be connected to a tap. If they are suitable for feeding a tap (which I think most/all other than 'over-sink' ones must be), then they surely must be equally usable with any type of shower mixer (including a thermostatic one) - since 'control' of hot flow by a thermostatic mixer valve is no different (from the point-of-view of the heater) from manually turning a hot tap.

Kind Regards, John

 

[ban-all-sheds]

No they relate to ones which are not like that. You could try following the links instead of presuming.

And no - they are not necessarily suitable for use with any sort of mixer, for the reason I outlined earlier. If the mixer reduces the flow of hot water in order to lower the temperature of the output, the hot water temperature will increase, requiring the flow to be reduced some more. Which makes the temperature rise even more. Which requires the flow to be reduced even more.

It's not hard to see where that leads....


I'd love to be proved wrong about no instant heaters being OK with thermostatic shower mixers, as I'd love to be able to do something like this:

so if anybody can find a reputable make which can be used, please let us know.

Until then I'll repeat my advice to check with the maker of any heater that it can be used with a thermostatic shower mixer.