Hi all

I've come across these products which extract the heat from your waste shower water, infuse the heat into incoming mains water and you then mix this heated up incoming mains water with your hot water while you're having a shower. Saves lots of energy apparently. It's approved in Appendix Q as well...

More info: http://www.shower-save.com

This seems great. Almost too good to be true.

Anyone got any experience?

Cheers

A friend of mine in Canada makes them - he has one in his own home. Works as advertised. See http://web.mac.com/winstonworks/http%3A__www.inventure.ca/Drainergy.html - he also has a version which works with intermittent sources such as baths, dish washers, washing machines etc.

I was going to install one at my house but our annual hot water bill is so low that it would not be worth it. We us only around 2000kWh a year on gas (mainly hot water - the rest is cooking) as the GSHP pre-heats the gas hotwater tank when we're heating (or cooling). Winter gas consumption is around 100kWh only per month (i.e. less than $2 worth).

Paul in Montreal.

Gotanewlife, is this what you're thinking of? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4403

When I was a student I used lots of bubblebath - worked well to keep the water hot. Letting the water go cold is an easy way to recover the heat.

Paul in Montreal.

I had thoughts on this kind of heat recovery but my only worry is buildup of soap etc within waste pipes as I have been called out quite a few times to blocked waste pipes and found it due to soap/waste products within the pipes. One lady had a daughter with severe excema and used copious amounts of lanolin in the bath water, hers blocks regularly!!.

Posted By: delboyThe kit costs around £500 for a house or £1000 for a flat. According to appendix Q calcs the £500 kit can save around 500kwh a year - 97kg CO2 or around a tenner.

Like so many bits of technology, good for the environment, bad for the wallet.

Would be interested to hear any first hand experience of the kit.

Cheers

OK, 500kWh for £10. This means an energy rate of ~£0.02/kWh. How are you heating your water, and what is the tariff?

No first hand experience yet but I have looked at WWHR for our house.

The calculations I have done on our household, taking into account my predicted usage of DHW for showers (2 adults + 2 children) shows a very different story. I think we could save 5-6kWh of energy per day, or something in the region of 2000kWh per year. At current gas prices this equates to a saving of around £130 per year. When the kids get to be teenagers I think this "saving" will increase as they take longer showers.

This gives a payback in a little over 3 years, assuming current energy prices.

SAP Q analysis in this case yields similar results - but around 25% lower since I estimate we will take longer showers than SAP assumes.

Originally I also assumed that it was not worthwhile if much of the heating comes from solar, but this turned out to be wrong. Recovering a significant portion of the waste heat means either that you can get away with a smaller panel, or that you can extend the period over which solar thermal can make a useful contribution to DHW. Either way, the heat recovery works out cheaper than the cost of panels it makes redundant.

As a result, we will be specifying a waste water heat recovery system for our new build. The only difficulty is routing the waste water from all of our showers into one recovery unit, but I think it's possible!

Yes, looks the business but I hate this sort of Web Site where there are no price details, small type and lots of space - you are left feeling sure that if you have to ask you can't afford it and that if you try to find out the price you'll get a hard sell. Do you know how much?

Mark Bennett the tenner a month is based on a gas boiler 90% efficient at 1.63p/kwh.

I know that gas has increased since that price (taken from SAP) but even if it triples it's still only £30 a year - 18 year payback

Posted By: davidfreeboroughWhy do we insist on using "payback" to justify not investing in carbon reduction?

Even if we accept that green technologies should be able to compete on financial terms, we don't assess savings accounts in terms of the number of years required to double your money. Investments are normally assessed in terms of annual percentage return, so why assess green investments in terms of years to payback?

Mainly because with an investment, at the end of the period you still have the original capital.

With equipment it depreciates in value over time, wear and tear, newer cheaper technologies etc. so that after a certain point in time (could be many years) the original investment is essentially gone.

Posted By: tonyMark but how much is the original investment worth in real terms after 18 years?

According to http://www.nationalarchives.gov.uk/currency/default0.asp#mid £1000 in 1990 has equivalent spending power to £1510 now.

So the original capital is effectively worth 2/3 of what it was. Does a 19 year old solar array have a resale value of 2/3rds of its install cost? I wouldn't think so, my guess it that it would be close to worthless to resell, certainly compared to its original purchase price. Of course, it can continue to be used and continue to produce useful green energy after it has paid for itself until it actually stops working, and this is where the profit comes in.

So, even though the argument to use payback rather than return on investment gets weaker the longer the effective life of the product we can't ignore the depreciation of the equipment. As an example, £1000 in 1975 is equivalent to £5570 now, so the original capital is only worth about 18% of it's original value, which is a big drop from 19 to 34 years and the value of the original capital is getting small compared to the value of the return on the investment.

(Of course, here we're purely talking about financial return, and not taking into account the other possible benefits - social and emotional.)

<blockquote><cite>Posted By: MarkBennett</cite>According to http://www.nationalarchives.gov.uk/currency/default0.asp#mid
£1000 in 1990 has equivalent spending power to £1510 now. So the original capital is effectively worth 2/3 of what it was.</blockquote>

This is also true for £1000 put into a savings account over the same period.

I take the point about not being able to easily reverse your decision & recover the capital, but the same is true of a number of investment products, for example, annuities. To use investment terminology, it is an illiquid asset & there are charges associated with recovering the capital, but that doesn't mean that we should write off the capital or ignore the profit after the capital has been repaid. That would be like ignoring an annuity's income after it has repaid it's purchase cost! If we did that then no one would ever put money into a pension. The risk is that if we stick to using payback then no one is ever going to put money into green technology.

David

<blockquote><cite>Posted By: Peter Clark</cite>I believe the only practical way to have the existing housing stock eco refurbished is to make it in people's financial interest to do so.</blockquote>

I agree completely. So why make the marketing more difficult than it needs to be by choosing a metric that no one selling financial products would choose to use? Why not allow people to compare investments in green technology with other investments they might make?

David

Posted By: davidfreeborough

Posted By: MarkBennettAccording tohttp://www.nationalarchives.gov.uk/currency/default0.asp#mid" >http://www.nationalarchives.gov.uk/currency/default0.asp#mid
£1000 in 1990 has equivalent spending power to £1510 now. So the original capital is effectively worth 2/3 of what it was.

This is also true for £1000 put into a savings account over the same period.

Yes, of course, but I don't see your point. My £1000 invested in savings in 1990 is now worth £666 plus any interest earned. My (hypothetical) £1000 invested in solar (or any other green technology) is worth nearly nothing plus any savings made . To make financial sense, the solar system has to recover the initial capital investment (you could argue devalued over the life of the product as if it were cash) in addition to any interest that would have been made on the investment. Hence we talk about payback time rather than return on investment.

Posted By: davidfreeborough

Posted By: MarkBennett
Yes, of course, but I don't see your point. My £1000 invested in savings in 1990 is now worth £666 plus any interest earned. My (hypothetical) £1000 invested in solar (or any other green technology) is worth nearly nothing plus any savings made . To make financial sense, the solar system has to recover the initial capital investment (you could argue devalued over the life of the product as if it were cash) in addition to any interest that would have been made on the investment. Hence we talk about payback time rather than return on investment.

I compared it with a savings product to make the point that cash would depreciate over the same period. Cash kept in your pocket will never break even. It will lose money every day that you hold it. This is not reflected in the payback period analogy.

Completely true. Everyone knows that inflation means that keeping cash is expensive. I'm assuming the comparison is between putting the money into a good savings account (long term bond would seem to be the most appropriate) vs investing in some form of renewable energy.

Posted By: davidfreeboroughI can see that it would be difficult to sell on your used solar equipment, but that doesn't mean that you should ignore the profit it continues to make once you've broken even. That ignores the most attractive aspect of the investment.

Of course. If the useful product lifetime is longer than the payback period then it becomes pure profit. In this case you need to depreciate the cost of the equipment over the expected lifetime and compare that to the savings/income generated to work out the return rate.

The bottom line is that you cannot just ignore the cost of the capital employed during the installation.

For those who take the time to do the maths, who know to take into account inflation, mortgage interest, etc, it seems like a detail. However, most people don't take the time to look at the calculations. They look at the payback period, decide they'll probably have moved house by then and dismiss the idea. I believe the payback period analogy glosses over the real issues and biases the decision towards people saying no.

In many ways the solar equipment is equivalent to an annuity, but instead of expiring when you die, it expires when the equipment dies. Would you buy an annuity if it was sold in terms of years to payback the money invested? For many people this period would exceed their own idea of their life expectancy & they would quickly lose interest.

I think we need to encourge a discussion in terms of return on investment versus cost of capital raised through mortgage, depreciation of equipment versus depreciation of cash in savings account, etc. The payback period calculation glosses over this and, in all cases I've seen, just ignores it.

David