Zoning a central heating system

[gsplum]

Hi, we are about to install a new central heating system and have received a couple of proposals. I would really appreciate some input from forum experts as to the best design.

We have a long narrow flat around 27m at its longest point. The pipes need to run above a false ceiling about 3m from the floor, or 1.5m from the comi-boiler. I have attached a PDF with three plans based on a two pipe reverse system (“the 3 pipe solution”) for the local loop and for the ceiling distribution:

(a) a simple loop from mid point to one end and on to the other end of the flat;
(b) a two zone design, with water heading off to either side of the boiler; and
(c) a 4 zone design which attempts to balance the number of radiators being served at each drop.

So the question is which is the best design? Or is there nothing in it given the lengths involved?

As a non-expert, I think the 4 zone design with local two pipe reverses loops is the best way to distribute the load on the boiler but a couple of installers have said a simple two pipe circuit with radiators placed in parallel and balanced manually via their lock shield valves is sufficient.

Our main concern is that we want to place thermostatic valves on nearly all the radiators so the initial balanced system may become unbalanced as the radiators disconnect from the circuit.

Many thanks in advance!

View media item 41271

 

[dcawkwell]

A single boiler will happily drive 10-15 radiators without any zoning.
Just lockshield and thermostatic valve on each radiator.

 

[gsplum]

A single boiler will happily drive 10-15 radiators without any zoning.
Just lockshield and thermostatic valve on each radiator.

hi dcawkwell, there are 16 rads and 3 towel holders, two of which are at the far end of the flat which has 550m3 of air to heat. I guess that's at the limit?

Does the amount of water flowing factor into whether to zone or not? I estimate there will be 50L of water in the tubes, 50L in the rads and 15L in the towel holders. Heat loss is 21kw so the flow rate needs to be 1500L/h for a target 12 degree system drop.

Also, wont the system heat up quicker in zones? In a single circuit (ie two tubes from boiler to furthest element which is a towel holder) the water has to travel 36m (with 8 drops, 16 rads, 2 towel holders) whereas with 4 zones, the average distance is 11m and the max 17,5m (with 3 drops, 5 rads and one towel holder) Surely a zone system will transfer energy faster to the furthest elements? And the energy loss per zone will be less for each complete change of water in the tubes? By extension, does the boiler not work more efficiently? Or is this just a startup concern?

 

[dcawkwell]

A single boiler will happily drive 10-15 radiators without any zoning.
Just lockshield and thermostatic valve on each radiator.

hi dcawkwell, there are 16 rads and 3 towel holders, two of which are at the far end of the flat which has 550m3 of air to heat. I guess that's at the limit?

Does the amount of water flowing factor into whether to zone or not? I estimate there will be 50L of water in the tubes, 50L in the rads and 15L in the towel holders. Heat loss is 21kw so the flow rate needs to be 1500L/h for a target 12 degree system drop.

Also, wont the system heat up quicker in zones? In a single circuit (ie two tubes from boiler to furthest element which is a towel holder) the water has to travel 36m (with 8 drops, 16 rads, 2 towel holders) whereas with 4 zones, the average distance is 11m and the max 17,5m (with 3 drops, 5 rads and one towel holder) Surely a zone system will transfer energy faster to the furthest elements? And the energy loss per zone will be less for each complete change of water in the tubes? By extension, does the boiler not work more efficiently? Or is this just a startup concern?

Zoning only controls if you have certain radiators in a common pipe work on or off. You can have one zone or four zones. It won't matter because if all the zones are open they are all calling for hot water. A pump can only move so much water and the boiler can heat only so much water per minute.
Most likely your radiators in Spain have fairly small requirements in comparison to UK heating requirements. Distances and heat loss in pipes
can for the average house be ignored so it doesn't matter if the radiator
is 50 metres away from the boiler or 5 metres away from the boiler.
So if you have 21kW heat loss and the boiler is 24kW it won't have much
trouble with the flat. Balancing the system should be much trouble as if you use thermostatic valves as parts of the flat heat up these valves will shut and water will be pushed into other areas. But I wouldn't expect much
trouble.

 

[simond]

Look at the new Honeywell EvoHome system.... might be of interest re zoning.

 

[Dan Robinson]

8)

 

[gsplum]

Look at the new Honeywell EvoHome system.... might be of interest re zoning.

Thanks for the info, its an interesting system but I think fitting each radiator with a thermostatic value will be sufficient in our flat.

Perhaps I am not using the right terminology. We are really concerned with the distribution of hot water rather than the control of heating in various parts of the house.

By 'zone' I mean individual branches from a manifold located at the boiler. A manifold with flow controls on each output would enable us to balance the flow of water based on the heat transfer required for the number of radiators on each branch. Thus balance the pressure in each branch.

Other replies suggest that this is not so important as the thermostatic values will change the flow based on the room temperatures in any case. Each local loop will use the "3 pipe" configuration.

I think its clear now that a single run of pipe that doubles back on its self (option 1 in the diagram) is not the best solution even if this would heat the lounge and dinning rooms first. The 2 zone (diagram 2) uses less piping and would give an even chance to each end of the flat at startup.

We have the chance to pick the best theoretical design, even if the difference is not very significant, whatever we save is less energy wasted.

 

[Dan Robinson]

Lummy, way to over think a heating system for a flat?