Central heating long runs

[akist]

Is there a way to calculate the energy loss over pumping C/H water around the house based on the pipes diameter and the length?

Can I use a 22mm pipe everywhere and forget about it?

If I have a zone which is far away, can I use a 28mm pipe to cover the distance and then drop down to 22mm/15mm to feed the actual radiators?

 

[Mottie]

I'd have thought 15mm would be better - less heat loss surely? How far a run are you talking?

 

[akist]

The house is two stories, 20m across and 14m width. The boiler will be at one end. I am trying to come up with a sensible design. All radiators will have wifi thermostatic valves.

Up to 5 minutes ago, I was thinking I need zones to separate parts of the house. I would like to pump C/H water only where it is needed to avoid losing heat. I was thinking one zone for upstairs, and two zones for downstairs.

But it has just dawned on me that if a TRV is closed, there will be no water circulation. And if a TVR is open, then you need to send C/H water to that radiator anyway, it is unavoidable.

In other words I can have a giant loop, connecting all the radiators together, and there is no need for "zones", because each radiator in the house will have its own thermo valve.

The question still is, if you need to travel 20 metres sideways, maybe 10-15 m down, then come back, do I need a 22mm or 28mm pipe for the long runs? Else the pipe itself would be a "restrictor" and that cannot be good, can it?

 

[oldbuffer]

1. I would be tempted to use:
1.1 28 mm pipe from boiler to the point where the last zone splits off.
1.2 22 mm for the spine flow and return in each zone.
1.3 15 mm from the spine to each radiator.
2. Insulate all the pipework with foam insulation with a minimum wall thickness or 19 mm.
3. Use 28 mm zone valves with reducers to 22m after the valves as necessary.
4. Don't forget the return from any hot water cylinder coil must be the last connection to the return before the boiler, otherwise you can get reverse circulation.
5. Determining the correct pipe sizes can be done more scientifically. Much depends on the Kw rating of the radiators.

 

[vulcancontinental]

Is there a way to calculate the energy loss over pumping C/H water around the house based on the pipes diameter and the length?

Can I use a 22mm pipe everywhere and forget about it?

If I have a zone which is far away, can I use a 28mm pipe to cover the distance and then drop down to 22mm/15mm to feed the actual radiators?

Get a pro who knows understands design principles, how to heat loss, calculate flow rate and pipe size. Plenty in Sussex I imagine.

 

[oldbutnotdead]

You need to do some sums. First set is heatloss to determine the radiator sizes.
Once you've done that you need to draw a schematic of the system (doesn't have to be geographically accurate, do mark leg lengths on the pipe runs and kw requirement on the rads. Allow 3kw for a hot water cylinder, as above make sure cylinder return is last tap before the boiler.
Once you've done that you can mark on your schematic how many kWh each leg has to carry when system is at full demand.
Have a look here Thread for some stuff on pipe capacities.
Do keep an eye on headloss as well in such a large setup- you might find you need a low loss header somewhere.

 

[akist]

OK so I have done the sums, all my radiators are 25kW plus H/W 3kW = 28kW.
A 28mm pipe will carry 38kW so I need to start off with 28mm at least, and then do more calcs for the individual legs.

Does this also mean a 30kW boiler would be OK?

 

[omph]

OK so I have done the sums, all my radiators are 25kW plus H/W 3kW = 28kW.
A 28mm pipe will carry 38kW so I need to start off with 28mm at least, and then do more calcs for the individual legs.

Does this also mean a 30kW boiler would be OK?

Does the average house even need 28KW for heating ? most could get away with 10kW. We were using 8kW and fixing all the draughts alone halfed our comsumption to about 4-5kW,

 

[oldbutnotdead]

Sounds like 30kw will do, rather like electricity you can apply diversity calcs to pipework schemes, it's rare that every rad will be calling for heat simultaneously for a long time.
The risk with oversizing (according to Google) is extended response times and low water velocity leading to sludge buildup. You could (assuming cylinder is near boiler) have a short (500mm) 28mm out of boiler splitting to 22 for the cylinder and another 22 for the rest of the heating. Yes for optimum response time & water velocity you reduce tube size as you move through the network, in general you'll be pretty safe with the 22mm spine and 15mm drops to rads

 

[vulcancontinental]

I'm just taking stock of the situation: you don't know how to do the job so quite reasonably ask opinions.

This is a substantial property although 28kW is very high and doubtful you will need that much.

Your post explains your doubts about pipe layouts but not how you have determined heat loss or how to calculate pipe size or pump head and flow rate.

This is your home I assume; if you can't afford to get it done properly, wait until you can because eventually it will need to be done properly.

You've got advice from posters using Google and comparing a property of unknown size and construction requiring 4-5 kW at an unknown external temperature with one the details of which are largely unknown to them other than it is 60' long and 42' wide which is not insignificant.

This seems a risky enterprise but good luck.

 

[akist]

you don't know how to do the job

Absolutely, my personal knowledge and experience is very limited.

I have used online BTU calculators to size the radiators in each room, and then adding some on top. Also comparing with what was there before and how warm/cold the house was.

This seems a risky enterprise but good luck.

Yes it is.

requiring 4-5 kW at an unknown external temperature

Yeah, we have spent 30,000-32,000 kWh gas and 10,000-12,000kWh electric since I can remember. We seem to be spending exactly the same in another house we have moved into, while other house being built. Daily this is like 11kW gas average for 8 hours a day, 365. The new house is more than double the old one...