Shower Heat Recovery

[mike2016]

Hi,

Has anyone installed a heat recovery unit for the shower / wet room? Just wondered if it's worth the effort / risk of failure vs marginal waste heat recovery? I was looking at the Passive House component database and they had a section on it, this one caught my eye as it was the best performing (just listed as an example only):

http://www.showersave.com/qb1-range/

I might look at including something similar in my build, a horizontal one for the wet room and the vertical one for the ensuite shower. 

Just curious what people's thoughts are on these generally? 

 

[ragg987]

I looked at the option before starting my build. The maths suggested benefit was marginal, and just another thing to go wrong.

 

Now if multiple showers can share one of these then this might change.

 

It seems best use would be to heat exchange against incoming cold mains water from outside. Complicates the plumbing quite a bit.

[Jeremy Harris]

I looked at a few options, from the rather dubious looking "Heat Squirrel" (I had real worries about the state that the holding tank would get into, and wasn't at all convinced it really met the water regs) to some of the (then) expensive linear systems.  The major issue seemed to be the requirement in the water regs for an air gap between the fresh cold water and the warm waste water, and even if as small as possible, this hits the efficiency a bit.  Some look reasonable though, and I have a feeling that @jack has one of the better ones fitted.

 

I even looked at making one, as the cost when I was first looking of buying one was so high that it would never pay for itself.  The things I learned were that vertical is best, that the waste inlet to the main vertical pipe needs to induce a high speed swirl to the waste water, so it sticks to the wall of the pipe as it goes down, for best heat exchange, that the regs require some sort of twin wall with an indicator that either the waste or fresh water pipe has developed a leak (tough to design in for a home made unit), but that if you were prepared to ignore the regs I think it would be pretty easy to make  unit.

 

My plan was to use a bit of 50mm copper waste pipe, with a swirl-inducing offset inlet at the top. This would be over 2m long and arranged to fit vertically down from the shower to a suitable drain on the ground floor.  For the cold water feed, I intended to wrap four parallel runs of 8mm microbore copper pipe as tight to the 50mm pipe as possible, to maximise the contact area.  If not overly fussed about the water regs, I'd have soldered the four pipes to the 50mm pipe to get better heat conduction.  Joining the ends of the 8mm pipes to a 15mm pipe at either end was going to be done with a small manifold.

 

I reckon I could have built one for under £100, a price that meant it would probably pay for itself in three or four years.  Whether it would have been worth the effort I don't know!

 

The problem doesn't exist if you use a bath - just leave it to cool before emptying it and you recover most of the heat back into the house.

[MikeSharp01]

AS JSH SAYS  @jack has a system and it has been discussed here a year + ago.

Edited March 10, 2018 by MikeSharp01

[MikeSharp01]

59 minutes ago, JSHarris said:

 

I reckon I could have built one for under £100, a price that meant it would probably pay for itself in three or four years.  Whether it would have been worth the effort I don't know!

If you felt it was going to pay for itself wouldn't the effort be worth it in the end? Or is the complexity just not worth it? 

[Jeremy Harris]

5 minutes ago, MikeSharp01 said:

If you felt it was going to pay for itself wouldn't the effort be worth it in the end? Or is the complexity just not worth it? 

 

TBH. I had so much on at the time that it got overtaken by events.  It was going to be a fair bit of work, so it was one of the things that ended up on the "don't have time to play with this" pile..............

[jack]

We feed the drains of two showers into our system. Our family situation means that we frequently have two showers in a row in the same shower. I think this tends to maximise the efficiency of the system.

 

We have a 250L UVC that's heated by an ASHP to 55 degrees (we also used to boost the top quarter of the tank with an immersion heater but in the end stopped doing that). We've never run out of hot water, even when four of us have showered in quick succession

 

My thinking was that in a low energy house, DHW becomes a dominant user of energy. Showers are the most significant user of hot water, so it makes sense to reduce that if you can.

 

Even if the maths didn't show a quick payback, I still think that a decent reduction in energy usage is a nice-to-have.

 

As for complexity, there was a little bit of extra plumbing, but other than that it's pretty much set and forget. I suppose I should check whether it needs cleaning internally every now and again, but I haven't managed to get around to it yet.

[mike2016]

Interesting about the air gap for regs - I'd have the thought the space between the shower head and the drain would have met that requirement (!), the fact you're dealing with flows in completely separate pipes - shouldn't matter if they snuggle closely, do they think you'd have two pin holes exactly opposite each other I wonder?! 

The kit I looked at above is over 1K so that might knock things back. I'm going passive so unless one of the showers is going to be used multiple times a day I'm less enthused but still like the idea of it. Great to hear about one in action though, between my plan of ashp & pre-heat, sunamp pv, inline water heater (Thanks JSHarris) and this heat recovery I think if I get this all working one day of setting up a shower challenge with Jack and see how long we can run the hot water for.....pruned to bits but shower happy! 

 

[Jeremy Harris]

1 hour ago, mike2016 said:

Interesting about the air gap for regs - I'd have the thought the space between the shower head and the drain would have met that requirement (!), the fact you're dealing with flows in completely separate pipes - shouldn't matter if they snuggle closely, do they think you'd have two pin holes exactly opposite each other I wonder?! 

The kit I looked at above is over 1K so that might knock things back. I'm going passive so unless one of the showers is going to be used multiple times a day I'm less enthused but still like the idea of it. Great to hear about one in action though, between my plan of ashp & pre-heat, sunamp pv, inline water heater (Thanks JSHarris) and this heat recovery I think if I get this all working one day of setting up a shower challenge with Jack and see how long we can run the hot water for.....pruned to bits but shower happy! 

 

 

The water regs require that foul water/grey water be run separately from fresh water, hence the need for the twin wall and air gap.  It's to prevent the risk of cross contamination from the waste water to the freshwater running alongside it, should a pipe develop a leak.  This makes a lot of sense in most respects, as shower waste water will almost certainly contain coliform bacteria, given the British habit of using toilet paper rather than a bidet or loo with a proper washing capability.

[jack]

That said, the shower water in the drain is at ambient pressure, while the water in the incoming cold water pipework is at 3 bar. I'd like to see faecal coliforms swim against a leak outputting water under 3 bar pressure!

[Nickfromwales]

2 hours ago, mike2016 said:

Interesting about the air gap for regs - I'd have the thought the space between the shower head and the drain would have met that requirement (!), the fact you're dealing with flows in completely separate pipes - shouldn't matter if they snuggle closely, do they think you'd have two pin holes exactly opposite each other I wonder?! 

The kit I looked at above is over 1K so that might knock things back. I'm going passive so unless one of the showers is going to be used multiple times a day I'm less enthused but still like the idea of it. Great to hear about one in action though, between my plan of ashp & pre-heat, sunamp pv, inline water heater (Thanks JSHarris) and this heat recovery I think if I get this all working one day of setting up a shower challenge with Jack and see how long we can run the hot water for.....pruned to bits but shower happy! 

 

You wouldn't possibly be having a Sunamp PV if you have an ASHP . You'd maybe instead be going for a Sunamp dual port that takes in wet heat as well as PV based electricity. That way you'd maximise the efficiency of feeding it with heat energy when the PV isn't up to it.

Far less parts and complexity too, that all said bearing in mind that Jeremy has the flagship model and the available range of Sunamp units has grown significantly of late.

[Onoff]

So.....if my boy comes home from uni with one of the foreign girls he's mentioned will they be expecting a bidet?

[Nickfromwales]

Just now, Onoff said:

So.....if my boy comes home from uni with one of the foreign girls he's mentioned will they be expecting a bidet?

Better than expecting a child 

[MikeSharp01]

11 minutes ago, Nickfromwales said:

Better than expecting a child 

Chilling!

[Nickfromwales]

Just now, MikeSharp01 said:

Chilling!

Inevitable !

[Ferdinand]

I have these in my list of things to look at for future rental refurbs, on a single shower version, because

 

1 They should give some benefit.

2 They have been around enough that prices may soon reach non Green-gadget levels.

3 They should be fit and forget with no moving parts.

4 I am told they are low hanging fruit for a couple of points off the EPC, and I am regulated on that basis but the definition changes every few years so it may be a useful buffer against the slings and arrows.

 

Remember to think about furring up of pipes if in a hard water area.

 

Ferdinand

Edited March 11, 2018 by Ferdinand

[jack]

3 hours ago, Ferdinand said:

4 I am told they are low hanging fruit for a couple of points off the EPC, and I am regulated on that basis but the definition changes every few years so it may be a useful buffer against the slings and arrows.

 

At least one of the sellers of these units suggests that they're the cheapest way of getting some extra EPC points.

[SteamyTea]

How do they work with a bath as you are not drawing water at the same time as expelling it.

 

Taking @JSHarris's idea a bit further.  Why not use a heat pump.  Run the expanding gasses around the waste pipe, squeeze that gas into a heat exchanger and see what comes out.

Edited March 11, 2018 by SteamyTea

[jack]

20 minutes ago, SteamyTea said:

How do they work with a bath as you are not drawing water at the same time as expelling it.

 

They don't. Most are designed solely to work with showers.

[MikeSharp01]

11 hours ago, Onoff said:

So.....if my boy comes home from uni with one of the foreign girls he's mentioned will they be expecting a bidet?

No not necessarily but a bathroom would be good. 

[Onoff]

8 minutes ago, MikeSharp01 said:

No not necessarily but a bathroom would be good. 

 

Depends where she's from, a hole in the ground might be all she's used to! The fact it's got a roof...luxury!

[MikeSharp01]

1 minute ago, Onoff said:

Depends where she's from, a hole in the ground might be all she's used to! The fact it's got a roof...luxury!

Hmmm not sure that is a PC view and besides you need quite some infrastructure around you, acceptable toilet facilities of your local standard probably being among them, to get the qualifications necessary to gain entry to your son's uni no matter where in  the world you come from. 

[Ferdinand]

2 hours ago, jack said:

 

At least one of the sellers of these units suggests that they're the cheapest way of getting some extra EPC points.

 

My comment was from a member of GBF. 

 

I have not run it it through the EPC software to check yet.

[Onoff]

1 hour ago, MikeSharp01 said:

Hmmm not sure that is a PC view and besides you need quite some infrastructure around you, acceptable toilet facilities of your local standard probably being among them, to get the qualifications necessary to gain entry to your son's uni no matter where in  the world you come from. 

 

Tbh I was hugely impressed at most of these foreign kid's grasp of English. Puts our foreign language teaching to shame.

[MikeSharp01]

44 minutes ago, Onoff said:

Puts our foreign language teaching to shame. 

Not quite true. Our problem is that we would have to teach many (100s) of languages to speak to them in theirs while they only have to learn one. I think we have discussed this before but max bangs per buck would be chinese and urdu but we teach french, German and Spanish none of which alone help you speak to the others. So while we are the custodians of the global 'lingua franca' ( oh the irony) there is no incentive for us to learn languages en mass.