Hot water recirculation- - an energy disaster? « Alternative Technology Assn Forums

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Hot water recirculation- - an energy disaster?

(24 posts) (19 voices)

Started 12 years ago by sandystone
Latest reply from Diver

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sandystone
Member

As a Home sustainability assessor, I have seen the energy / home situation many times over the past 6 months.
I have witnessed 2 houses with these Hot water recirculating pumps, and they both had ENORMOUS energy bills- ie 80 and 90 KWH per day for each household .
To clarify- one house was on off peak HW, and that component of the bill was 40 KWh per day! (the other on smart metering)

The other place that had one had an 800 litre capacity hot water (2 x 400 ltr) and I could access the first 8 metres of hot water pipe coming from the tanks. The entire thing was too hot to hold! In both cases, the energy was being wasted to space in vast quantities.

I imagine a much better system is to use small dimension hot water lines- ie 16 mm so small volumes of hot water are wasted, and thick insulation over the entire system would be a better solution. - and get rid of the pump.

Experience shows, many plumbers have little regard for customers energy bills, or any concept of energy conservation principles, so there is little or no insulation on any of the hot water systems mentioned, or most others I have seen.

Any other similar experiences? would be interesting to hear about them....

Posted Tuesday 12 Jan 2010 @ 7:22:24 am from IP #
ghostgum
Member

Our solar + instant gas system had insulation on copper pipes, but no insulation on plastic pipes. The plumber said that the plastic pipes were as good as insulated copper pipes. Turns out he was partly right - from memory they were as good as copper + 3mm lagging. But they could be improved, so I used some left over polyurethane foam lagging to insulate the pipe between the hot water system and the kitchen. It takes 3 litres to get fully hot water at the kitchen tap. Pipe insulation means that the dish washer has a better chance of getting warm water for anything after the first cycle (and so doesn't have to use electricity to heat it). At least half the lag is just getting hot water through the copper pipes and instant gas system to under the house before the plastic pipe starts.

Posted Tuesday 12 Jan 2010 @ 9:49:02 am from IP #
munter
Member

80-90 kwhr/day!!! Wow. That is certainly an example of a case where the inspection should yield enviro benefits.
Hot water recirc can be an example of overoptimising one variable (water) at the expense of another ( power).

Posted Tuesday 12 Jan 2010 @ 9:49:53 pm from IP #
LanceTurner
Key Master

Yes, have to say I'm not a fan of these systems, the prob is they are usually added to existing plumbing, which is rarely properly insulated, so there's no choice really, the energy bills have to go up. But, there are some systems that only circulate on demand (can't recall the names at the moment), so they don't waste energy, and return the water normally wasted by running water through until it's hot back to the tank. So, they don't really save energy (although some suppliers were claiming they did - dubious claims at best) but they can save water. But then, all you have to do is have a container at the ready to catch the waste water and dump it in your rainwater tank, if you're organised you can do this and not need a recirculating system, and you save the cost of the system plus the pump running and maintenance costs. The old KISS principle...

Posted Tuesday 12 Jan 2010 @ 11:52:12 pm from IP #
CNCandy
Member

We were told about a water device called a chilli pepper during out HSA course that returns cold water back into the system before exiting the hot tap . Would something like this work in your situation?

Posted Thursday 14 Jan 2010 @ 5:44:51 pm from IP #
gully
Member

Yep the chilli pepper does this, though some people think it's a problem if the unit ever fails.

The best way to do it would be to have a ring-main hot water system where you can circulate water in a loop with a low-power pump (without pushing against mains pressure), but as sandystone pointed out if they decide to run continuously, buyer beware!!!

You're really just sacrificing energy (power) to save a little water.
Over-optimising if you ask me, too.

Get a big watertank and plumb it to your house, and do something with your grey-water rather than bother with this.

Posted Thursday 21 Jan 2010 @ 5:32:06 am from IP #
Skysolarman
Member

sandystone

hot water circ pumps are a good idea as long as you use a timer with it , set them up to circulate the water an half an hour or so before peak time usage otherwise let the timer keep them turned off. The Grundfos UP15-14B version comes with an integrated timer

Posted Thursday 21 Jan 2010 @ 9:46:40 pm from IP #
Gold Ideas
Member

Hello all.

Found a solution. http://www.redwater.net.au failsafe device, no power, no switches, no problems.

Posted Friday 29 Jan 2010 @ 6:45:54 am from IP #
Michael L.
Member

My only experience was years ago in the UK. Our 2 storey house had a coke water heater on the ground floor that fed a tank in the upstaris bathroom and radiators in the upstairs bedrooms. No pumps required, the system used normal thermal circulation, as the water cooled it returned to the boiler. The only hassle with them was blowing off trapped air every now and then through a small relief valve, don't exactly know where the air came from, or maybe it was steam?

Posted Monday 1 Feb 2010 @ 11:33:04 pm from IP #
acd
Member

We put in a dux recirculator last year as our bathroom is at the far end of the house from the hot water service (long thin 80s house). It used to take > 5min running the shower full tilt to get the water hot. I tried carrying buckets but its also far from the garden, my husband wouldnt do it for his showers and I hurt my back. The Dux is just a pump connected between the cold and hot pipes in our bathroom (under the basin). We press a button when we want a shower and the cold water in the hot pipe is redirected to the cold pipe. It has a sensor and the pump turns off when the water gets warm. so when it turns off its time to shower. Even my husband will press the button! I still think its a little miracle when I turn on my shower and it actually comes out hot! Theres a $150 rebate but the cost is considerably more, so it doesnt really make sense from a budget viewpoint but it works for me.

Posted Wednesday 9 Jun 2010 @ 2:19:35 am from IP #
dymonite69
Member

I agree with Lance they are water savers, not energy savers. You save energy by insulating the pipes and hot water tank.

If you want to save water put a grey water diverter in and get it to work for you twice.

Posted Saturday 12 Jun 2010 @ 12:00:33 pm from IP #
Buzzman
Member

Here's another one that has some video and animations on the site http://www.advecotech.com.au/

Posted Sunday 13 Jun 2010 @ 7:16:44 am from IP #
Gold Ideas
Member

I looked into the return speed for the Redwater Diverter. It does infact speed up the delivery of hot water due to the fact that the return line is not subject to flow restictions that are on your shower or sink. Also - I think that pumping hot water back into your cold lines in many cases is far from ideal. Obviuosly there are now ways of saving redwater and greywater to use the water three times.

Also looked into the ecoverter thing. They have done a cheap copy of the redwater technology. I think the redwater is still cheaper. I bought mine for $176.

Posted Monday 26 Jul 2010 @ 3:06:12 am from IP #
Daniel Boon
Member

plastic pipes are NOT to be used in hot water applications.
Lagging - insulating - copper pipes is a must, any plumber or otherwise who tells you differently is having you on ...

Its like saying sarking is insulation, when its sole purpose is an attempt to be a water proofing membrane ...

Posted Tuesday 27 Jul 2010 @ 12:14:59 am from IP #
ghostgum
Member

I must be missing some context here. PEX plastic pipes can be used in hot water applications, but only if the temperature is below about 80C. So you can't use them between solar panels and the storage tank, but you can use them after the temperature regulating valve.

By sarking, do you mean RFL? If so, it acts as both a water proofing layer and also as a radiant barrier (if correctly installed).

Posted Tuesday 27 Jul 2010 @ 12:42:48 am from IP #
olfella
Member

In other threads we've been discussing the cost & efficiency problems resulting from inadequate insulation on hot water pipes & sensors which can cause excessive circulation pump activity in evacuated tube solar systems, based on the flawed temperature sensing.
It flabbergasts me that anyone would want to have a standing recirculation for the convenience of instant hot water throughout a house. Effectively it is a energy disappation system, regardless of the extent of lagging.
Surely the environmental waste through energy usage far exceeds the value of the wastage of a few litres of cold water. What we're really talking about here is bad system design, with the hot water system either the wrong type for the application, or located in the most inappropriate position for the house. Otherwise it is just a straight out wasteful lifestyle choice. No doubt many such systems end up being retro fitted as a quick fix because of bad design, without an understanding of the implications. I would think installation of instantaneous gas boosted systems would be less costly & more efficient in the longer term.

I have real problems with the design of so many open plan modern houses & the so-called innovations they incorporate. All too often add-ins are problem solving, but seldom pay attention to conservation or energy efficiency; both of which are actually issues of long term cost.

Posted Tuesday 27 Jul 2010 @ 5:31:11 am from IP #
dymonite69
Member

Olfella is so right.

We tried to design our house so that the HWS was mounted equidistant between the furthest two points of the wet areas and had the shortest run to the kitchen where water is most frequently turned on an doff.

Posted Tuesday 27 Jul 2010 @ 6:38:56 am from IP #
GBD
Member

I don't think they are that useful as energy savers and the diverting options are better IMO as the water can be used in a garden etc.
I know of a passive house that put the hot water pipe through the slab and in their first summer the house was really hot (solar HWS) and they found it was the hot pipes in the slab that was generating the heat.
They've now put a manual 10 minute push button switch on the circulator pump - when they get up or want to have a shower - they push the button - it circulates the water for 10 minutes and they have a shower with instant hot water at the tap.

Posted Tuesday 27 Jul 2010 @ 7:44:35 pm from IP #
Russell Moore
Member

I have mentioned this before in a similar thread, but all we do is run the 'hot' tap water into the bath until it becomes hot, and when the bath is half full or so, I syphon it out onto the garden. Gravity is my pump.

Posted Tuesday 27 Jul 2010 @ 10:22:00 pm from IP #
Buzzman
Member

My Mum had similar situation to acd's - HWS at one end of the house, bathroom at the other. But the HWS was near the kitchen, so not all bad.
Mum had my plumber brother install a recirculating pump, but her enregy bills went thru the roof!! Like a 30% increase in cost. So she switched it off.
Lance is quite correct, they are water savers rahter than enegy savers, but tend to come with a degree of 'self-perceived entitlement' - ie: we are "entitled" to have our water hot at the tap!! Wait til this get's added to the next Bill Of Human Rights....liek the 'right' to own a car; or a jetski; or a gun...etc etc
From an eco point of view, only a system which returned the 'waste' cold water via gravity could be considered to have no eco cost.
But those systems like Redwater and Ecoverter that utilise existing mains pressure can be a useful solution, as the cold water can be forced into a holding tank or garden watering line, thus getting full use of the water without wasting any more energy.
The only thing that is 'wasted' is the homeowner's time - and that can be avoided with practice and a bit of common sense.

Posted Tuesday 27 Jul 2010 @ 11:50:22 pm from IP #
peterj
Member

I recently installed a demand activated hot water recircualtor in my house that I got from Reece. It means that i press a button and it draws the water up to the tap. Once the hot water arrives it beeps at me and I get hot water staright away . Fantastic and really cheap to run !. and I got $150 REBATE (VIC ONLY I THINK)
see link: http://www.reece.com.au/plumbing/products/9502995

Posted Thursday 9 Feb 2012 @ 5:08:46 am from IP #
dbindoff
Member

It looks like it saves some water at cost of energy to run + embodied energy and materials in the device - then it looks like you may inadvertently get some 'somewhat warmed' water at one or more 'cold' draw off points, which may be ingested - not recommended, I think, to drink water from a hot water service like this?

My question is, why would Vic govt be giving a rebate to a small water saving device and be promoting coal-fired power stations at the expense of renewables - given that coal-fired power consumes an inordinate amount of water?

Posted Thursday 9 Feb 2012 @ 5:44:24 am from IP #
peterj
Member

Given the time it takes for the water to arrive I have calculated I will save some where around 22k litres per year with a running cost of under $5 per annum. The Reece product not only saves water coming into the property but also reduces my sewerage charge for water leaving the property. I have spoken to the EPA re the issue of injesting any hot water and they have no evidence that this is harmful

Posted Friday 10 Feb 2012 @ 2:57:13 am from IP #
Diver
Member

peterj said:
I have spoken to the EPA re the issue of injesting any hot water and they have no evidence that this is harmful

Good on 'em!

Hot water service sacrifical anodes corrode.

Some anodes are aluminium.

Most people would not have a clue as to the type of anode they have.

The dangers of ingesting aluminium is well documented.

What has this to do with the EPA anyway? Maybe they weren't considering HWS's.

Posted Friday 10 Feb 2012 @ 7:10:45 am from IP #

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