"IMM" wrote in message
...
"John Aston" wrote in message
.. .
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)
Aiden has highlighted some points, so I will not go over them. Some
observations and Qs:
Firstly, what drawing package did you use, Visio?
The boiler appears to be a Veissmann with an in-built outside weather
compensator with the temp sensor in the low loss header. If the
compensator
slope is set to the UFH, it will not be suitable for the rads. You would
require the low loss header to be on the minimum temp that the rads take,
which means a higher temperature for the boiler to operate on making it
less efficient. If you set the compensator slope for the higher temp rads,
each the UFH zone will control itself on its own mixer controls, set to
maximum of 55C.
You could use a dual temp boiler as the Eco-Hometec, or a simple boiler
maintaining a hot low loss header at a high temp. This is what is done
with
non-compensating boilers where the return temp "has" to be high. So, as
you
have it the rads will not go about 55C.
The mains water from the accumulator. As you have done in splitting the
DHW
supply to the cylinder after the accumulator, and cold water. But! have
all cold taps off one leg. On the other supply only the cylinder. With
the
exception of just before the cylinder have the cold supplies to the
showers
only.
Have only one pressure reducing valve as mixers require equal pressure on
each inlet line. Using an accumulator means you only need cheap shower
mixers.
If you assess the heating requirement to 32Kw then stick to this, or the
nearest to, depending on price. No need to go over for DHW as you have a
priority system. This diverts all the boilers heat to the cylinder.
Make sure the cylinder is quick recovery. Unvented cylinders are never as
quick as vented or thermal stores. The coils are restricted so as not to
generate too much pressure inside.
Do you still intend to have two stage heating? UFH with rads boosting?
Yiou have 5 UFH ziones. Where will the rads fit in relating to these
zones?
Back to having differing temps for rads and UFH. As it is, efficiency is
compromised by the high temp rad circuits. You have an efficient expensive
boiler not performing to maximum potential. Look at the low loss header
on
the diagram. Replace this with a heat bank/thermal store. Off the bottom
UFH section of the thermal store have the UFH circuits. Off the high temp
top section have the rads and DHW. You may want to have three sections:
top
DHW, middle rads, bottom UFH. Then you have all circuits coming into a
neutral point, the heat bank.
Now you have greater control of temperatures, dividing and ruling, which
means the boiler will not be running at too high a temperature to suit
only
the rads compromising efficiency. An outside weather compensator can be
on
the UFH section to keep this part of the store at the ideal high efficient
low temperature and prevent boiler cycling. You may want a compensator on
a
heat bank mid section serving the rads (UFH & rads have different slopes).
Using a heat bank, a far cheaper and simpler boiler may be used.
Having three sections means that in summer, only the DHW top section is
heated, not the whole store, saving on standing losses.
Using a heat bank immersions may be fitted in the different temperature
sections. So, if there is a boiler outage you can run the whole system,
heating and DHW off electricity. You can't do that with a boiler
connected
via a low loss heater.
I forgot to mention. Insert two low loss headers would not cure this
problem. A priority system would need to be in place favouring the rads.
The problem is that the headers do not contain enough mass. In a heat bank
the top rad section could re-heated rapidly and left for while for the rads
to extract the heat. One up to temp it reverts to UFH temps and heat the
lower section. So it would switch from UFH to rads with long intervals
between. This cannot be done with a small mass header. In effect a heat
bank is a very large header
Towel rails: These can be teed in before the diverter valve at the
boiler,
between valve and pump and direct to the return. They will then work in
summer, but only when the cylinder or heat bank is being re-heated, which
is
fine for summer use. If you take a shower and the boiler kicks in the
re-heat you will find the towels are hot on the rails.
Accumulator: If they will not sell unless they supply the unvented
cylinder
(they would sell one separately to me), keep a tank in the loft and have a
booster pump serving a heat bank. This is a cheaper an simpler option too.
The tank does not need to be in the loft. It can be anywhere as it is
pumped.
It would be interesting to see what the Yanks say. They don't do thermal
stores in a big way there and thinking tends to be 1950ish, so only regard
what they say as interest only.
Simpler Alternative:
1. Low Temp Circuit: One dedicated condensing boiler serving the UFH only
on a weather compensator. Simple, separate and sorted.
2. High temp circuit. Another boiler using a 3-way diverter valve
serving
DHW and rads. You may want a weather compensator switching the boikler to
give the ideal temp for the rads. When DHW is called the boiler runs up
to
max temp. This is similar to normal domestic setup.
3. A controller staging in the UFH and rads to give precise control of
room
temps. UFH 1st stage.
4. Backup: Now you have heating backup if one boiler drops out.
Electrical backup for DHW.
5. Cold water storage tank instead of an accumulator with a booster pump.
Tank can be fitted anywhere.
6. The cylinder can be:
a) An unvented version,
b) A DHW only heat bank, such the DPS Pandora, which does requires an
overflow so can be fitted anywhere in the house.
You will find that two condensing boilers can be had for less than the
price
of the Viessmann, and lots of change too.