On Mon, 15 Nov 2004 16:40:21 +0000, John Aston wrote:

Thanks for your help to date. I've distilled the advice from various threads
in this newsgroup to come up with a possible heating design for my house.

The drawing HD01 at http://tinyurl.com/3zv2g shows the proposed hydraulic
design for a large domestic heating system. The boiler and hot water
cylinder is on the left hand side of the drawing, space heating is on the
right. (You might need to rotate the view so that the drawing is in
landscape orientation in your browser)

Some explanatory notes on the design are appended below. Any comments would
be gratefully received but my principal questions a

(1) The internal space heating requirement when it's -3°C outside is 31kW.
In addition, there is a 250L cylinder serving three showers and one bath for
a family of five. Is a 38kW boiler sufficient?

This is similar to a system I installed a couple of years ago. with a 170L
HWC and a Keston C40 (that's about 37kW output but runs at about 35kW due
to service main inadequacy). It works fine. Except I used a 5-way S-plan
and no UFH.

Since this is a sealed primary what does the 'top up' unit mean?


(2) I'm specifying 28mm pipe through the water softener and up to the
cylinder, 22mm for the boiler flow and return, 22mm to potable water cold
taps and 15mm everywhere else. Is that reasonable or over the top?

It's going to be quite some softener unit to process the flow that requires 28mm
pipe 8-)
Main Boiler flow and return should likely be 28mm even if only to the
diverter valve and last return T. Most boilers of this size wil likely have 28mm/R1
connections.
Cold: 22mm for the garden tap. Other wise it really is OTT.


(3) A 22mm pipe is teed off the secondary side of the low loss header. From
this 22mm pipe, I propose to tee off 15mm pipe to each heating zone. What is
the maximum distance between these 15mm tees, and what's the maximum
permissible distance from the furthest 15mm tee to the header? (Keston told
me that there is NO restriction)

Provided they leave and return in the same order. You have check valves to
prevent back flow in the inactive zones. It might mean you need a higher
pump setting for the farther zones.



(4) What's the best way of incorporating two towel rails (bottom right) into
the circuit so that the towel rails come on all year round when there is
either a call for heat or a call for hot water?

Right off the boiler flow and return, suitably balanced against hogging
all the flow.


Design:

The mains cold water supply is treated by a water softener (bottom left).
The softened water is fed to a 250L cylinder under pressure from an
accumulator which keeps the cold water at about 2.5 bar and provides a high
flow rate to all taps.

I take it that you have an inadequate water main?



The water in the cylinder is heated indirectly by the primary of a 38kW
fully-modulating condensing boiler in the room below the cylinder. Hot water
is circulated to the taps by means of a secondary pump. Because the system
is unvented, the hot water is also at a pressure of about 2.5 bar.

Bronze pump needed will (cost will equal total of all the other pumps). 8-(


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html