Shower heat recovery devices/combi boilers

[PullerGas]

Hi there,

Disclosure first. I am a professional engineer in Ontario, Canada and have a master's degree in engineering here. My specialties are alternative energy systems, heating ventilation and air conditioning and hot water systems. I am also the inventor of the Power-Pipe Drain (Waste) Water Heat Recovery Technology. We now have well over 60,000 Power-Pipes installed and saving energy every day in homes, flats and in some commercial and industrial applications.

Original Question: will a properly designed/made Waste Water Heat Recovery (WWHR in the UK) “boost a combi’s DHW supply sufficiently to cope with 2 decent showers at once?”
Yes, absolutely and certainly in your case. Of course this depends upon the efficiency of the WWHR unit at the total flowrate, your combi boiler’s capacity and how it is installed. Basically, with a 55-60% rated WWHR unit you can generally expect a doubling of effective hot water capacity. Many WWHR devices have been installed to solve the problem of insufficient capacity with on demand water heaters, for example.

Contrary to Dan Robinson’s reply, WWHR is not snake oil. It is proven and well established (in some places) technology. In fact, the AIMC4 Project in the UK found the hot water savings to be 35% and 41% in two different homes with a Power-Pipe R3-84 (not the most cost effective model but it forms part of the main soil stack). At a 2011 AIMC4 meeting in BRE Watford offices I informed the 60+ attendees that I expected that model would save 35% to 40% of the hot water load. They thought I was crazy. However, this was based upon over a decade of experience and monitoring at the time. The current SAP (UK building energy credit) calculations have 7 errors, which result in only about half the SAP credit that WWHR devices should receive. Our industry has been trying to get this fixed for almost 2 years. The AIMC4 project report demonstrates this gap. I have included the core pages from the AIMC4 report. You can also download it at: http://www.aimc4.com/filelibrary/files/AIMC4-Briefing-Paper-5_final.pdf

Contrary to bernardgreen’s comment, waste water actually clings to the inner wall as it fall down a waste pipe because of “surface tension”. The quicker it falls, the better the heat transfer, because the film of waste water becomes very thin so there is less resistance for heat to flow to the inner wall. In fact, a University of Waterloo professor found that the heat transfer rate in the falling film is higher than through copper! Slowing the film down somehow will actually decrease the heat transfer rate.

Also, using a tank, as described by bernardgreen, with a WWHR domestic device is a bad idea (we do that for some industrial applications) because you don't get the counter flow and do not have the high heat transfer rates. However, keep in mind that a falling film WWHR device primarily captures heat energy from the shower, which is the main load in homes. Most falling film WWHR devices are very efficient, perfectly safe, maintenance-free, passive and have a very long life making them quite practical.

For highest energy savings and ease of installation we normally recommend that all the fresh water in the home be plumbed through the WWHR device, except the kitchen sink. The WWHR device does not hold the water at any temperature so the water will fall back to room temperature (like all the lines in the home) when not in use. It can and usually does recapture some heat from other fixtures, if they are plumbed to it, but we are primarily interested in getting the waste water from the shower(s) and plumbing to both the cold side of the shower and to the water heater/cylinder. All the water in my home runs through my Power-Pipe and, honestly, it is not a problem. It even takes the cold edge off the water so we usually wash our hands with the cold water line (actually tempered water from the Power-Pipe).

endecotp, WWHR devices will certainly supply the capacity that buffster is interested in if:
-the water heater / cylinder is not already very marginally supplying the one shower
-an very inefficient WWHR device is not installed (be above 40%, but depends upon the water heater)
and/or
-it is not installed for equal flow as described above

endcotp has mentioned the Recoup units (models we’ve seen) are relatively efficient. The Recoup units we have seen are partly made of drain plastic and the double wall is not actually externally vented so if there is ever a leak between the walls you wouldn't know it. Furthermore, the inner copper wall thickness does not confirm with British standards for a 2” (54mm) pressurized line (which it is on the external). WRAS approval doesn’t deal with these points. The other models mentioned are all solid examples of WWHR technology. All are falling film and vented, maintenance free and should have a very long life.


It does not make economic sense to combine a WWHR device with a heat pump in a home. There is some interest in doing this for large apartment buildings and hotels.

I might come back with more comments. I do agree also that having a good lower flow shower head is also important for reducing energy consumption and increasing capacity.

Respectfully,
-Gerald Van Decker

Forgive us Gerald, we do enjoy a wee joke & a bit of banter, but all the pros are at heart very interested in all aspects of our industry. So to that end; you've clearly studied UK Plumbing & Heating systems in depth, how does it compare with North America?

 

[bernardgreen]

A couple of comments and questions

every day in homes, flats

How would you install a WWHR unit in a flat ? Doesn't it depend on there being several feet of vertical space below the shower ?

Of course this depends upon the efficiency of the WWHR unit

How long does a WWHR unit reman as efficient as it was when new ? How is efficiency affected by the build up of slime, soap scum and other materials commonly found adhering to the inside walls of waste pipes ?

with a 55-60% rated WWHR unit

Exactly how is this 55-60 % rating derived ? What is ( was ) actually measured

waste water actually clings to the inner wall as it fall down a waste pipe because of “surface tension”

How much surface tension is there in water that has had detergent added ? The intention of detergents and soap is to reduce surface tension to improve the cleanng action.

In fact, a University of Waterloo professor found that the heat transfer rate in the falling film is higher than through copper!

Is that through the water in the film ? It is likely that it was movement in the water carried the heat from one side of the film to the other side. So not conduction ( as has to occur in the copper ) but by convection which is a much more effective way to move heat.

are very efficient, perfectly safe, maintenance-free, passive and have a very long life making them quite practical.

As before how is effective / efficient life affected by build up of detritous on the wall of th pipe. ?

Who funded the research at University of Waterloo ? It is known to have very low funding for research projects which might suggest it would spend that limited funding on projects with more financial return for the University's funding needs.

 

[JohnD]

Couple of questions for Gerald:

I heat my hot water using a cylinder and gas boiler. The cost of gas in summer (CH off, so just the cost of gas for HW) is £7 per month.

How much do you think I might reduce that by with a heat exchange device, and how many years do you think it would take to recoup the cost of purchase and installation? As you know, many UK residents (including me) do not take long hot showers.

My shower room is on the ground floor. How much heat might be recovered in the three-metre horizontal waste pipe before it joins the soil stack and goes underground?

What (if anything) would I save if I fill a sink with hot water to wash pans, then pull the plug out 15 minutes later?

 

[Dan Robinson]

Interesting questions chaps.

8 suspect they will highlight the difference between lab tests and the real world....

SAP, MPG anyone?

 

[DP]

Couple of questions for Gerald:

I heat my hot water using a cylinder and gas boiler. The cost of gas in summer (CH off, so just the cost of gas for HW) is £7 per month.

How much do you think I might reduce that by with a heat exchange device, and how many years do you think it would take to recoup the cost of purchase and installation? As you know, many UK residents (including me) do not take long hot showers.

My shower room is on the ground floor. How much heat might be recovered in the three-metre horizontal waste pipe before it joins the soil stack and goes underground?

What (if anything) would I save if I fill a sink with hot water to wash pans, then pull the plug out 15 minutes later?

If you can harness the heat generated during some postings, hot air that is given off by somme useless postings not to ignore flatulence, collectively, this will result in authorities giving you a rebate for the energy produced.

 

[bernardgreen]

Here is some of the documentation of the research into drain water heat recovery in university buildings that was carried out by second year students at University of Waterloo.

http://environment.uwaterloo.ca/research/watgreen/projects/library/f03drainwaterheatpac.pdf

one of the contributors was

Van Decker, Gerald. President of RenewABILITY Energy Inc. November, 2003.

 

[big-all]

picked up this quote from the front page
"
Unlike most
environmental or “greening” initiatives, however, the economic limitations in this
case are non existent. Installation of this product should become quite profitable
within a relatively short amount of time."

comment like that can come in summery after the experiments have been completed not before
"quite profitable within a relatively short amount of time"
for who not the end user as the buying installation and maintainence costs must be recouped first that will not happen in a" relatively short amount of time"

"the economic limitations in this case are non existent"
of course they are limited the best you can scavenge is 100% but the limiting factor is far lower probably nearer 5-10%
the use off such flowery language is designed at best to mislead at worst to decieve

 

[endecotp]

I think you're all being a bit too sceptical.
I think the issue is really just the cost, and hence long payback period. But that could improve - the devices are quite simple and the materials shouldn't be expensive.

 

[Ash Prescott]

Hi,

I see Gerald has not responded, but a few answers to some of the questions that have been asked-

How would you install a WWHR unit in a flat ? Doesn't it depend on there being several feet of vertical space below the shower ?

Yes, with the WWHR installed vertically you need a vertical drop, so it is not something that would benefit the ground floor flat/bathroom. The WWHR unit is used to service the 1st floor and above. Something worth noting is that a single WWHR unit can be used to service multiple bathrooms/flats/apartments.

Exactly how is this 55-60 % rating derived ? What is ( was ) actually measured

They are SAP rated efficiencies, calculations of which can be found here; http://www.ncm-pcdb.org.uk/sap/file...aneous_Shower-Method_Statement_22.11.2013.pdf

An easy way to (theoretically) illustrate this is that a unit rated at 60% efficiency will be producing a pre-heated water of output of 60C if the cold input was 0C and the waste hot water going into the unit was 100C, at a specified flow rate.

Most of the other questions here point to WWHR 'real life performance'. The data from AIMC4 showed that WWHR saved 35-40% on water heating energy with the 8 best performing households in terms of hot water energy use were all using WWHR. FYI AIMC4 was a 'real life' performance test using the general public and conducted over a 2 year period in the UK. As Gerald mentioned he has been doing this for a long time all over the world and 35-40% is the typical recorded saving.

I think the issue is really just the cost, and hence long payback period.

One of the most cost effective units is a Power-Pipe R2-60 with a list price of £350 ex VAT & delivery. If that were to save 400kWh per person per year (based on AIMC4) then with gas at 4.5p kWh with a 2 person occupancy your looking at a payback of around 10 years, or if it were a family of 4 it would be around 5 years. The point being that this is of course dependent on the amount that the shower is used by the household and the number of occupants.

As you know, many UK residents (including me) do not take long hot showers.

As far as I am aware, the typical shower length in the UK is 8 minutes and falls in line with the recorded energy savings above. This is based on the following independent studies;

http://www.telegraph.co.uk/news/ear...e-as-much-water-and-electricity-as-baths.html
http://www.theguardian.com/environment/green-living-blog/2009/sep/04/power-shower-blog

I hope the above is useful..

 

[JohnD]

If that were to save 400kWh per person per year

Which is £10.62 per person per year. One eighth of the cost of my hot water.

So a cost of £350 would take 35 years to repay. Add on delivery, VAT, installation cost and the opportunity cost, what are we looking at? 70 years?

gas at 4.5p kWh

Please also explain why you would want to pay 4.5p per kWh when it is currently available at 2.656p plus 5% VAT

My shower room is on the ground floor. How much heat might be recovered in the three-metre horizontal waste pipe before it joins the soil stack and goes underground?

What (if anything) would I save if I fill a sink with hot water to wash pans, then pull the plug out 15 minutes later?

No answer?

 

[Ash Prescott]

Please explain how that is possible when the cost of my hot water is £7 per month.

Your hot water use would appear to be quite low. How many people are living there and do they all bathe at the property regularly (as opposed to using work or gym facilities for showers etc)?

Please also explain why you would want to pay 4.5p per kWh when it is currently available at 2.656p plus 5% VAT

4.5p is based off uk average taken from here: https://www.gov.uk/government/statistical-data-sets/annual-domestic-energy-price-statistics
Also if you look here http://www.energysavingtrust.org.uk/corporate/our-calculations the price is more or less the same.

2.656p sounds like a very low figure, perhaps not including a standing charge?

 

[bernardgreen]

R2-60 with a list price of £350 ex VAT & delivery

For a basic concentric tube exchanger 3 metres long using small quantity retails pricing
3 metres 22 mm copper tube £ 13
3 metres 28 mm copper tube £ 20
2 off reducing T 28 x22 x28 £ 6

Sundries £ 10
total materials cost less than £ 50

Half an hour of labour £ ? so a concentric is very low cost.

The R2-60 does have 3 parallel tube that are flattened and wrapped around the drop pipe. This may add a bit to the cost of materials but with the benefit of lower cost bulk buying of copper tube I doubt the material costs of the wrap round are much higher than the concentric.

I hope the above is useful..

Useful in showing how much hype is applied to the product

 

[JohnD]

Two, yes

You are quite wrong to imagine that the standing charge will reduce. I am charged 18p per day by my supplier. I can reduce or increase my gas usage by 10%, 60% or 1,000%, it is still 18p per day. I think you are not familiar with the difference between Fixed Costs and Variable Costs.

Therefore, you are wrong to think that by reducing your usage by say 400kWh, your bill will drop by more than (400 x the price of 1kWh) = (400 x 2.656p) = £10.62 plus 5% VAT

You are very wrong to publicise marketing estimates based on a false calculation.

I hope that nobody actually selling these things sells them by telling customers these false numbers.

 

[bernardgreen]

An easy way to (theoretically) illustrate this is that a unit rated at 60% efficiency will be producing a pre-heated water of output of 60C if the cold input was 0C and the waste hot water going into the unit was 100C, at a specified flow rate.

100°C waste water, I doubt it happens in normal houses

at a specified flow rate.

There would need to be two specified flow rates to give any meaning full results. How much hot waste water and how much fresh water.

 

[Dan Robinson]

This whole thread is nothing but a pathetic marketing exercise. Have the mods checked the ip addresses of the posters?