View Full Version : Heat loss in water pipe

15-02-2014, 06:56 PM
Hi chaps.

I have been asked to provide hot water and underfloor heating by means of a heat pump and intend to use Daikin Altherma. The building is an office block with 3 toilet and shower areas. One in the middle of the building and one at either end. I am looking to site a hydro box and a hot water cylinder in the middle of the building and then pump hot water in either direction to the other 2 areas. My client has spoken to their plumber who is concerned about heat loss in the pipe work as the total pipe runs will be approx 40 meters in either direction. I had hoped that if the pipe work was properly insulated this would not be an issue. Now the question has been asked I really need some maths to back it up! Can anybody help me with how I would go about calculating the potential heat loss from the pipe run?

The Viking
15-02-2014, 08:25 PM
The problem in your case is time...

If your hot water taps isn't used over night or over the weekends then you have to assume the water in the pipework get cold, regardless of insulation.
How long will it take the hot water to flow from your hydro box to the taps? Longer than it takes to wash your hands?

One option would be to have circulated hot water but that do add to overall system energy consumption.


install monkey
15-02-2014, 08:40 PM
if the cylinder is mounted near to the toilet area on the middle floor then its only a small domestic hot water circuit so sticking a bronze circ pump and a secondary return isnt a big job- the 40 mtr runs for the underfloor heating that you coud lose performance/capacity

15-02-2014, 09:05 PM
To comply with Legionella regulations you will need a fully pumped secondary circuit for the hot water service.

If you don't pump it then you will need to fit electric trace heating to the pipework.

Don't forget the blending valves required at the wash hand basins as well.

16-02-2014, 09:03 AM
Thanks guys. I think the plan is to have a fully pumped secondary circuit to comply with the legionella regs. I am only supplying and installing the heat pump side of the system not the water side of the system so what they do with it is really up to them. Obviously I just need to confirm that we will get sufficient water temp after the 40m runs they are proposing on both the hot water and the under floor heating? The underfloor heating is only being used in the toilet blocks so there isn't much load, only 4 or 5 thunder boxes per block. Rest of the building heating will be VRV Brian, could you enlighten me further on the blending valves required? I am booked in for an Altherma course next month prior to install but I am a bit stuck at this the design stage as I am clueless about the water side of the system!!

install monkey
16-02-2014, 09:14 AM
mixing valve- to regulate the tempout the tap- so your secondary circuit is ideally 60deg but if you turn a tap on the maximum you get out the tap can be regulated to say 40deg max-you dont need 1 per sink- 1 can do multiple sinks

16-02-2014, 09:25 AM
Cheers install monkey! I guess these are pretty standard in any hot water service so plumber should have covered. I think the water temp out of the hydro box into the cylinder is about 50 deg C. The controller is programmed to do a legionella protection cycle once a day where it brings on the immersion heater and raises temp to 60 Deg C for 2 hours.

install monkey
16-02-2014, 11:20 AM
best to programme the legionella protection to kick in outside normal occupancy time- your dhw circ pump should be on a timer to only circulate hw during open hours then your using less leccy to power the heaters

16-02-2014, 12:30 PM
Yeah I think it's pre-set for midnight but that's something to check. Good shout on the pumps. Hopefully the Daikin kit might have some external connection options and we can wire pumps through a contactor and control via remote. If not a good old time clock should do it!

16-02-2014, 07:21 PM
The inbuilt Legionella cycle on the Altherma is factory set for once a week, not once a day.
The 3 port diverting valve must be fitted within 3m of the Hydrobox, and the cylinder must be fitted within 12m of the Hydrobox, as the cylinder temp thermister comes with a 12m lead and cannot be lengthened

16-02-2014, 08:41 PM
I knew it was once a 'something'! Week makes sense though I guess. The only info I have on Altherma is from half an hour with a Daikin sales engineer last week. I originally designed the building with a separate Altherma to serve each of the 3 toilet blocks. It was Daikin who suggested that I just use one larger system and pump it off it either direction. I have put this to the client who would gladly except the cost saving. He has spoken to plumb who is now questioning the amount of heat loss in the water pipe runs?

17-02-2014, 12:13 PM
Insulate the pipework and put in the circ pump. I tend to wire the pump to the light switch so it only needs to run when someone is in there, thus saving energy. There have been VERY FEW times that this has not been sufficient.

17-02-2014, 12:48 PM
as much as it pains me but Space Air are probably better at the altherma than DUK as Neil took this as his new baby and really run with it. they will be a better bet for the spec etc.