Affordable heating option for new SAP regs.

[jack]

Yes, I know you can do all that, but it isn't a linear as, say, measuring how much water is in a bath and determining its temperature.

 

For example, when you first get into the shower, it takes some unknown amount of time to come up to operating temperature.  Efficiency is initially zero, and then rises to maybe 50% recovery when it reaches equilibrium.  But every day is different - two longish showers in a row will allow much higher average efficiency out of the unit than two shortish showers an hour apart, but you're more likely to run out of hot water with the longer showers.

 

So yes, you can work out some really rough and dirty numbers, but it's a big and complex step to do much better than that.  

1 hour ago, MikeSharp01 said:

What system are you using for this, should be possible to get an idea shouldn't it, amount of water x temp delta x efficiency of the system or have I missed something, only looked at such systems in the first stage, have kept the waste water separate from the 'number 1s & 2s' to the plant room in case it looks like a worthwhile proposition. (Must add that to my post above about things to remember.)

From memory, we have the Recoup Pipe+ HE.  It was a toss-up between that and the Powerpipe - I don't recall why we chose the one we did!

[MikeSharp01]

Ok so two flow meters one in the waste water and one in the heat exchanger, four temp probes one in each input and output and a data logger! Then a bit of integration should lead you to how much you are getting back. The question is from / via where is it coming back!

 

Easier to use a pair of range assumptions. Assume 10% efficiency (worst case) so for every hundred litres of hot water you get back 10L and 64% as quoted in the Recoup literature (which is IMO more than you can expect and perhaps therefore a bit missleading) and get back 64L I think not!!!! The answer will be in that range somewhere, probably nearer the the middle than the top. You could look at it another way.

 

1. You only shower in hot water so you don't really care about the inflight cold water at the start of your shower but you need to know how long it runs cold for, call it ifh.

2. You shower for 4 minutes and use 40L (10L/min) @ 40degC @Nickfromwales would approve.

3. Plus (and this is where the time derived form 1 above is important) you have left ifh seconds of hot water inflight to the shower head and it is now cooling down and it won't go through the Recoup device. Lets say ifh is 15sec (I would hope a lot less!) you have actually used 42L of water @ 40 degC.

4. So you loose almost 7% that you cannot recover, so even if perfect only 93% is available to recover.

5. Some heat will be lost as the water cools, flowing over you - a somewhat cool 37 degC, the shower tray, down the plughole and along the pipes to the Recoupe device. Lets say it drops by 5 degrees. (You could measure this with an IR device at the top of the recoupe device I guess)

6. So once the HW hits the Recoupe its down to 35 degC so its given up another 17.25% (assuming your incoming CW is at 6 degrees) of its heat

7. You now have just 40L of water at 35 degC now only carrying 76% of the heat you lovingly put in at the generator end.

8. Now multiply that 76% by the 64% efficient (assuming system A and the recoupe figures) and you get 49,25%

9. I think that means you might get back about 49% of the usable shower from the Recoupe device itself!

 

BUT because you have a neat little MVHR most of the heat coming from the inflight hot water now standing in the pipe, the heat given off by the shower tray and pipes as they cool and that generated by your good self giving yourself a good rub down with a towel (you may of course be lucky enough to have somebody else doing the rubbing down in which case you can double the output) will be kept in the house anyway so in a very real sense you get much of that back also. Not unreasonable to expect the MVHR to be 90% efficient. Extending this idea a little further we find that its not so much how much you get back but rather only how much actually goes to waste having run through the Recoupe device. It looks like a good proportion of rest is kept about the place via the MVHR.

 

Hmmmm... I think I will go and have a snooze after that and contemplate not bothering with traditional waste water heat recovery but just slow the output flow down enough to let the MVHR pick up heat from the pipes as they cool... and just let it go in the summer!

 

 

 

 

[jack]

Interesting numbers.

 

To be honest, In the past I've just assumed it's somewhat worse than they say it is, so a very rough 35-40% recovery, on average.   If it's probably better than that (as suggested by your numbers), then great!