Shower waste water heat recovery

[snootsandfruits]

So as the price of energy continues to rise, and without having a solar system to throw an extra panel at, I'm considering fitting one of these (Recoup Pipe HEX) as part of our retrofit (yeah wrong subform now, blame the OP )

In practical fitting terms, the shower is going to be almost directly over where there's currently some pipes boxed in below in the kitchen, which is being totally redone anyway, and the main waste is also right next to this, albeit on the outside of the house.

It'd be a run of perhaps 4m of pipe from the hot outlet to the intake of the new hot water tank, and about 2m to the cold of the new thermostatic shower control.


Any required maintenance should be easy so long as the boxing in is designed to accommodate at least removal of the top and bottom connections to the unit. I suspect that the swirly top part is the most likely to clog up, especially if sufficient long hair catching is not done at the shower drain.

[Stinsy]

This is one of those "sounds like a good idea, doesn't work out" kind of things.

I know, I know, you used energy to heat the water, it shoots past your body and straight out the drain. There has got to be heat worth "recovering". Right?

Well the first, and biggest problem is that there has to be two walls between waste and potable water (shower water = potable). So your rate of recovery is terrible. Next the devices and all the extra plumbing is onerously complex and expensive.

[AE-NMidlands]

and think of the embodied energy (i.e. carbon dioxide emissions) in the extra plumbing...

(That's my big grouse about electric cars. The hype completely ignores embodied energy in what we have now, often perfectly servicable and maybe - used sparingly - less energy-intensive than a new electric car. We just found our car keys in the safe from before we went away for Christmas! Errands since have been done by bike or walking and bus home, so we hadn't noticed. We would have had to dig the keys out tomorrow as we want some apples out of the store in the garage...)

I would shy away from anything complicated involving waster water simply because of the potential need for cleaning it out: doing the ordinary traps and the manifold under the sink is more than enough for us!
A

[Tinbum]

I came to the conclusion it wasn't worth it.

If I do decide to use the heat from the waste water then I will just run a long horizontal waste pipe by placing the waste pipe in the floor slab further away. Easy to do with I beam floor joists. And for the bath, the plug won't be pulled until the waters cold. (New house so condensation shouldn't be a problem).

[snootsandfruits]

So your rate of recovery is terrible.

You say that, but the efficiencies are not terrible. >60% is in my books very good for such a simple product.

The device itself is clearly still quite expensive (maybe £650 with some isolators, a check valve and p&p), but the additional plumbing is sod all as I'll do it myself (and it's all being redone anyway), and the additional hassle of install is minimal as a remodel is happening anyway.

It feels an easy win when everyone in this house likes to have pretty long showers, and hot water heating is when the heat pump will be running at its least efficient. A 50% saving on energy use, and a 50% larger effective hot water cylinder when visitors are over sounds good to me.

and think of the embodied energy (i.e. carbon dioxide emissions) in the extra plumbing...

In our case it's basically exactly the same amount of pipe (including the length of the thing) due to where the stop tap is and where the hot water cylinder is in relation to the shower. It's no additional plumbing, just slightly rerouted plumbing.

In pretty much any case, surely a heck of a lot less than the energy that it can save over its life time.

[AE-NMidlands]

So your rate of recovery is terrible.

You say that, but the efficiencies are not terrible. >60% is in my books very good for such a simple product.

The device itself is clearly still quite expensive (maybe £650 with some isolators, a check valve and p&p), but the additional plumbing is sod all as I'll do it myself (and it's all being redone anyway), and the additional hassle of install is minimal as a remodel is happening anyway.

It feels an easy win when everyone in this house likes to have pretty long showers, and hot water heating is when the heat pump will be running at its least efficient. A 50% saving on energy use, and a 50% larger effective hot water cylinder when visitors are over sounds good to me.

and think of the embodied energy (i.e. carbon dioxide emissions) in the extra plumbing...

In our case it's basically exactly the same amount of pipe (including the length of the thing) due to where the stop tap is and where the hot water cylinder is in relation to the shower. It's no additional plumbing, just slightly rerouted plumbing.

In pretty much any case, surely a heck of a lot less than the energy that it can save over its life time.

So what are you paying £650 for then?
And I would be very suspicious of a claim of >60% efficiency.
You need to see the test protocol, and find out what is being measured. I wouldn't be surprised if it took "waste" water at 100 deg (just for standard/repeatable conditions, of course) and incoming at 15 (roughly normal) or even 10 or 5 to get the best outcome. Also what flow rates?
If 2 skins are needed by "law" that will dramatically lower the performance too.
I can't remember what we paid for our N******n solar thermal system, probably not more than 3 times your gadget, but it heats the cylinder from May to Sept every year and almost boils it in mid-summer.
A

[Tinbum]

If I was going to install one I'd make my own. I have a length of large diameter copper pipe somewhere.

[snootsandfruits]

I can only find the testing procedure for storage WWHR systems, but I imagine that the procedure for testing standard WWHR is much the same in terms of temperatures.

Inlet water temp of 13C, waste water temp of 34C
(https://www.ncm-pcdb.org.uk/sap/filelib ... -_V1.0.pdf)

I was surprised when I first saw the efficiency figures but they are properly tested, or otherwise the systems would not be useable as part of a building's SAP.

No idea on the flow rate, but it's probably something sensible.

The one I mentioned gets around the two skins thing by having two pipes that have effectively drainage channels in between them - there's plenty of direct contact, but a leak is highly unlikely to end up through into the fresh water, rather coming out of the bottom. Some others have copper pipe wrapped around, similarly with some gaps.

So what are you paying £650 for then?

WRAS certification, and the fact that there's not a lot of competition in the space and house builders will consider it a small amount to pay for how cost effective it is for their SAP score.

[snootsandfruits]

Recoup Pipe HEX:


I imagine that this is the absolute maximum amount of surface area that they're allowed to have shared between the two before they're considered to be directly contacting one another.

[Paul_F]

Well the first, and biggest problem is that there has to be two walls between waste and potable water (shower water = potable). So your rate of recovery is terrible. Next the devices and all the extra plumbing is onerously complex and expensive.

They're getting much better. A few years ago they were at 30% and £2k - now it's twice the efficiency and half the price.
For a new build it may even be cost-neutral: it looks like our heating system will be sized by the recovery time on the hot water cylinder. As showers are the main user, something which reduces the shower hot water consumption significantly will act like it is upsizing our heat pump for heating hot water, which has a far bigger impact than a small reduction in heat demand. Solar doesn't help with this, as the design point is on a cold day with no sun when we will have our max heating demand.

So what are you paying £650 for then?
And I would be very suspicious of a claim of >60% efficiency.
You need to see the test protocol, and find out what is being measured. I wouldn't be surprised if it took "waste" water at 100 deg (just for standard/repeatable conditions, of course) and incoming at 15 (roughly normal) or even 10 or 5 to get the best outcome. Also what flow rates?
If 2 skins are needed by "law" that will dramatically lower the performance too.
I can't remember what we paid for our N******n solar thermal system, probably not more than 3 times your gadget, but it heats the cylinder from May to Sept every year and almost boils it in mid-summer.

• Shower waste is at 40°C, hot feed from the cylinder at 60°C, not stated what the cold feed is at. Warm but not ridiculous - and efficiency would go up if the flow temperature was lower. The efficiency measurement comes from the temperature difference between water to drain and cold water in - colder shower waste inlet means a colder waste outlet.
• The "twin skin" thing is a bit of a fudge - looks like they shrink-fit one pipe inside another or something very similar, so to all intents and purposes they're a single pipe. Does provide pretty good protection against a manufacturing defect I suppose.
• So we have two systems which both provide about half of the heat for showers over the course of a year. One from our former hosts is 3x more expensive and needs to go on the roof where you could otherwise put PV. The other is fitted in a cupboard where you'd need a pipe anyway. If anything the heat exchanger is more valuable since it still provides heat in midwinter when PV, etc. is not available.

So what are you paying £650 for then?

WRAS certification, and the fact that there's not a lot of competition in the space and house builders will consider it a small amount to pay for how cost effective it is for their SAP score.

Main market for these is volume housebuilders, who will NOT be paying £650 a pop.