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Our ASHP system now seems to have settled down and the house is warmer throughout.
One problem that I would like to sort if it is possible is the heating of hot water which then cools down in the pipes, necessitating the running off of the cold water before we get hot water. In our house this amounts, over a year, to be a quite a lot.
I remember reading that running a pipe to the lowest tap/point back to the hot water tank was a solution, is this the solution?
Any ideas.
 
This is secondary circulation, this will possibly cost you more in heat lost and new pipe runs, new circulating pump etc, but you will have instant hot water.
Have a look into lagging your pipes properly, or even trace heating.
 
As Subby has stated you could install a secondary circulation system, the new circulators that are coming onto the market are far more efficient than there predecessors both in the power they use but also how they are controlled some have built-in clocks & thermostatic controls others are self learning about when you use your hot water & will only start at these times. All the pipework will need to be insulated & if you have an un-vented cylinder don't forget that you may need to add more expansion capacity due to the increase in hot water.
The trace heating is a self regulating heat tape which is applied to the hot pipe work & just keeps it hot until the next time it is used. This was often found to be more efficient that the secondary systems, it will be a lot easier to retro fit as well.
Hot Water Temperature Maintenance | Trace Heating Tapes
 
Ever used trace heating? i dont know if i like the idea of the water sitting there being heated by that rather than flowing around and back to the heat source being brought upto tempreture again. The mininmum the secondary water has to return at the cyl is at 55c, does trace heating keep the water that hot?
 
Ever used trace heating? i dont know if i like the idea of the water sitting there being heated by that rather than flowing around and back to the heat source being brought upto tempreture again. The mininmum the secondary water has to return at the cyl is at 55c, does trace heating keep the water that hot?
Hi Josh, it has been used for years, I used "H-Wat" I think it was called & it self regulates to maintain a water temp of 55 C, easy to install tape to pipe & the two cables which run through it are just made off with a simple kit & plugged into a 13 Amp supply easy !! Just make sure the insulation is up to scratch (had a problem cos I did not check it on a job once).
 
After having secondary circulation in my own dwelling for many years I can give some anecdotal evidence on performance, which repeat some of the points already made:

1. Bronze circulators are expensive and last about five years, due to soft water area.
2. Bronze circulators run on electricity further increasing expense. Noise and rattle, especially on mega-flow systems can be a problem.
3. Insulation needs to installed to a very high standard (the 9mm I fitted on mine 20 years ago is now costing me.
4. Brass Towel rails may be incorporated within the loop which gives summer warmth to towels, and heat in spring and autumn when heating is off.
5. Saves water, but questionable savings on energy for domestic systems.
6. Reduces risk of legionella but questionable on domestic systems.
7. Risk of scalding at tap, because heat is there instantly, so increase need for blending valves in public sector, and caution in domestic dwellings.
8. Increased recovery time for cylinder when drawing say one shower (whole cylinder dilutes to say 40 degrees c, needing whole volume to be recovered, because circulator running). This can be a real pain in mornings when hot water is needed.

In all it is a luxery to have secondary circulation, and I would say it costs me to heat the towel rail in my en-suite as much as the heating costs to run. So I consider it a technology of yesteryear for existing domestic dwellings (new build with solar options may be different).

Instead I would recommend point of use heaters where possible such as undersink displacement heaters with flow restrictors in the hot tap. They use this in Holland and have done for the last three decades, rather than having long dead legs for hot water. These also carry far less Legionella risk if you are specifying for public sector applications. In addition temperature can be more accurately set.
 
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I might be able to help you with a few of the list above like electrical usage & energy wasting (might have to loose the towel rails or they would be on for much shorter times, though).
Grundfos Comfort | Grundfos

Also from the larger multileged systems these will help thing of them as TRV for your HW sytem. [DLMURL]http://www.rwc.co.uk/images/pdfs/gplumb/thermbv.pdf[/DLMURL]
 
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Not 100% sure without looking but doesn't water regs state that any tap outlet more than 9m away from cylinder requires a secondary circ
 
Although i agree with some points of yours clanger i dont with all of them, 9mm lagging is never enough anyway and running a loop threw a towel rail is a bad idea, we had to put one like that a few years ago as it was on the drawing of an air source heat plan supplied and we all agreed it was a bad idea, you lag all your pipes then give all the heat away through a towel rail, seems silly.

Thank you for your reply Chris.

You have to be able to acheive 50c water within 30 seconds of running the outlet. (If it is not on a mixer obviously).
 
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Not 100% sure without looking but doesn't water regs state that any tap outlet more than 9m away from cylinder requires a secondary circ

Just for info Si H, I can't find anything in the reg's when a secondary circ has to be installed. I think it was in the old By-laws ? I think Josh is correct (next post) I am sure I have seen this 30 sec arrival somewhere although quite how you are going to predict this before the install I am not sure. Any ideas of where that 30 sec comes from ??
[h=1]R18.7[/h]Where the location of hot water outlets within a building require long lengths of pipe (dead-legs) to serve them, heat energy is lost in running water to waste until the water discharged at the outlet is at a suitable temperature. It is recommended that the length of dead-legs should be as short as possible, not more than those shown in Table G18.7, and all hot water pipes including those forming part of any secondary circulation system, should be thermally insulated.
Table G18-7.jpg
 

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I only know that Chris because we had our annual water inspection last year and got talking to him about this and that's when he said, i dont think i'v ever read it in a book tbh.
 
Hi
Thanks all for the info, first thing we will have to do is insulated the pipes which will be a problem because some are behind a wet wall and under the bath all very well sealed but I suspect some of the piping is not lagged. First use of the tap in the bathroom produces around 9 litres of cold water before we get any warm water especially at this time of year, this then kick starts the ASHP, the Nibe F2015 heats the DHW to 49 degrees no matter what, and the DHW side of the tank is 145ltrs, I think the trace heating may be the best option.
If taken over the population as a whole the waste of energy must add up to quite an amount!
 
Poorman, I'm guessing you have an unvented cylinder? If so you can reduce waste water by piping deadlegs to taps (basin and sink) in 10mm pipe. Assuming you have mixer taps the internal bore of the tap tails will be no greater than 10mm anyway (usually less), and an unvented cylinder will still give you sufficient pressure and flow, but obviously a lesser volume of water cooling in the pipe, and less time running it off.

Don't try this on baths/showers.
 
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