Blended hot outside tap from gravity

[fowlerboi]

Customer wants an outside tap for dog washing so needs to be blended. The hot water is gravity and its a bungalow so little head at the point of installation. I can't get a cold from the storage cistern to the utility so it has to be mains cold.

Can pressure reducing valves be taken down to 0.3bar and still function correctly or are the flow rates going to be pathetic?

Would Gravity hot water into a blending valve meeting a cold main reducded to 0.3 bar work well enough to wash dogs?

 

[Timmy D]

Usually they go down to about 0.5 bar.

 

[ShaunCorbs]

I wouldn’t you could pee faster

Think your not going to win

 

[fowlerboi]

Right so what about a 30L water heater? At 60c in the heater blended down to 30 (keeping it low to make the most of the hot water) you would get a 50/50 blend? Meaning 60L of hot water at something like 10lpm if I restricted it which would be easily enough to wash a dog you would get 6 minutes of dog washing. The customer has 5 dogs so that would allow for just over a minute per dog.

I'm no dog owner but would that be sufficient?

Looking for solutions before I tell her it can't be done

 

[ShaunCorbs]

Yep that’s the way I would go or and instant one but you will need a 40-50 amp electric for that

 

[Deleted member 120897]

What about a single impeller pump for dhw?

 

[MikeJhn]

In line shower booster pump, designed for the purpose of increasing hot water flow with indirect systems: Shower Booster Pump - https://plumbhq.uk/products/shower-booster-pump?

 

[fowlerboi]

Looking at something like this?

I've very little experience with booster pumps but the last one I did was recommended stuart turner and avoid salamander. Any other recommendations?

A water heater would be my prefered choice but I am a little worried about running out of hot water

 

[ShaunCorbs]

Pump would have to be at the cylinder via an s or e flange

 

[MikeJhn]

In line shower booster pump, designed for the purpose of increasing hot water flow with indirect systems: Shower Booster Pump - https://plumbhq.uk/products/shower-booster-pump?

Fitted one on the kitchen sink supply not near the cylinder and it works fine.

 

[fowlerboi]

Thats not going to happen otherwise I would have just taken a cold feed from the cistern.

Why would it need to be from the cylinder? I can't see how its any different than something like tap boost?

 

[ShaunCorbs]

Thats not going to happen otherwise I would have just taken a cold feed from the cistern.

Why would it need to be from the cylinder? I can't see how its any different than something like tap boost?

Would suck air through the vent

 

[MikeJhn]

Would suck air through the vent

Could you expand on that please, I can't see why it would suck air rather than just replacing the water through the inlet into the cylinder.

 

[fowlerboi]

Done a bit more looking at tap boost and can see why it wouldn't work, tap boost is only a minor increase and the pump would effect every other outlet when open. Not convinced it would pull air though, have fitted loads of digital showers just teeing off downwards and had no issues although I've never done a pump as powerful as 2 bar.

Back onto the water heater then, will just discuss with the customer about sizing depending on how much they want to use.

 

[MikeJhn]

Why does the pump need to be two bar? If its a gravity feed cold water outlet in a bungalow that's far too powerful if you want to blend with hot from an indirect cylinder.

 

[fowlerboi]

It needs to be balanced feeds so I'll bring the cold main down to 2 bar with a PRV and the gravity hot up to 2 bar with a pump. Can't be done without a new supply which I can't do so that idea is scrapped

 

[MikeJhn]

Forgot on the first post you said the cold supply will be straight off the mains, apologies for the miss-understanding.

Pampered pooch, immersion heater in a rainwater barrel if they must.

 

[Ben-gee]

You could use a Venturi shower valve, this works off tank hot and mains cold.

Used to use Trevi Boost but they discontinued.

I think ideal standard do one called boost too, did they take over Trevi?

Anyway a thermostatic Venturi shower is what you want!

 

[Timmy D]

Is the boiler near by? Could add a zone with a plate heat exchanger?

 

[OffgridKiwi]

On the time to wash per dog, one minute would be too short for even the smallest shortest-haired dogs.
You need to get them thoroughly wet all over, soap them up all over, and then rinse.
If the dogs are large and hairy, it can take half an hour plus per dog, especially if their coat is water resistant and needs a lot of working in to get wet. You can reduce water use by not running it when soaping them, but the wetting and rinsing can take a lot of time.