Review my Central Heating plan please?

[Mike Barnard]

Hi again.

Having looked at all your helpful posts recently and read as much as I can, I have drawn up a basic plan of how my CH should go. Please take a look at it and tell me if there is anything wrong with it or anything I should change?

1 is downstairs, Zone 2 is up.

I have a primary room (without TRV) in each zone.

I intend to use a pair of 'optimum start' (Honeywell CM61 or 67) controller in each primary room.

There is no room for a rad as well as a towel rail in the bathroom, but it has provided enough heat in the past.

The towel rail should take heat from any zone.

Of course, have a couple more simple questions, if may dare! :)

• Are the one way valves necessary? If so, are they in the right place?

• Am I right in putting the TRV's on the supply side?

Many thanks in advance.

Mike.

[Doctor Drivel]

No.

Yes.

[Dave Baker]

You don't need any of them as each zone is isolated by its zone valve and the towel rail circuit isn't affected by one anyway.

Makes no odds unless the TRV is uni directional and fitted on the wrong side of the rad. If the TRV is bi-directional it can go anywhere.

[:Jerry:]

Why should it matter?

[Doctor Drivel]

Convention. Also the restiction of the TRV is more easier overcome on the flow.

>

[Roger Mills]

They won't do any harm - but you don't really need them. As long as the returns from all radiators in each zone combine before the composite returns combine the zones will operate independently without needing non-return valves. If you insist on using them, they're in the right place!

It is usual, but not obligatory. The important thing - if the TRVs are directional - is to have the flow going the *right* way through them (there should be an arrow on the body). Some TRVs don't care, and others are bi-directional but *do* care - there's a little gizmo inside which has to be twiddled into the right place for your chosen flow direction.

[Doctor Drivel]

They will restrict flow.

[Fred]

Until now I've generally agreed with you. However with a virtually inelastic fluid such as water it doesn't matter where you put a resistance to flow. The pressure drop will be the same independent of pressure. Water temperature and it's corresponding change in viscosity will have a far greater effect.

[Dave Baker]

As someone with a more than reasonable knowledge of fluid mechanics including designing and building a flow bench to the specs in British Standard 1042 there won't be a scrap of difference to the restriction created by the TRV whether it's on one side of the rad or the other. You're just making this stuff up.

[Doctor Drivel]

In a vented system that is the case, as the pressure around the system can vary enormously. That is why non-return valves are ideally directly after the pumps. The effect is reduced dramatically in a sealed system.

[Doctor Drivel]

See other post.

[The Natural Philosopher]

Everything that Drivel posts is read from catalogues or made up.

None of it relates to any real world experience. Since he doesn't live there, he has none.

[Dave Baker]

I've looked at the manufacturer's fitting instructions for various makes of TRV and there's not a single mention that they are better placed on one side of the rad than the other as long as the flow direction is correct for the way the TRV is set. I'm quite sure that if there was even one miniscule reason for them to operate better on the flow side then someone somewhere would have said so. Similarly there isn't any reason that physics or fluid mechanics appear to offer to support your view about restriction.

The only conceivable distinction between the flow and return side is that the water temp will be lower on the return so the TRV won't have to cope with such large thermal effects from expansion and contraction and might possibly last a bit longer. So I'll continue to fit mine wherever there's the best access and airflow for them and you put all yours on the flow side if that's what you think you need to do. Just don't try and convince us there's any actual reason to do so though.

[Doctor Drivel]

TRVs have been around for 40 years or so and for the first 25 years all were to be on the flow only. Sealed systems are the normal now.

I regularly built my own heat banks, all vented. Take a pipe off the top of the cylinder into a plate heat exchanger, then into a pump then back to the bottom of the cylinder. Ideally it is best to have a check valve in the line to prevent natural circulation through the plate. Put one before the plate and the pump has to overcome the cylinder ahead of it and the plate before. The check valve will only be partially open most of the time. Put the valve directly after the pump and no probs. In theory it shouldn't make that much difference, some more positive and some more negative around the loop. I put pressure gauges on many points and the difference in pressure was marked.

A TVR on the return has the restriction of the rad before it.

Also the rad restriction.

Read above.

[Doctor Drivel]

You are a plantpot, a snotty uni one.

[John Rumm]

One thing I have noted with some so called bi-directional TRVs is that they can be more noisy on the return side when they start to close off the flow. I had one that whistled irritatingly until moved to the flow side.

[fred]

I agree that is the case for a vertically mounted valve but think it should be return side for a horizontally mounted valve. The generic case appears to be that the problem will be less likely to occur with the flowing pushing in such a way as would open the sealing washer. That said you'd be pretty unlucky to experience a problem but it's bloody annoying when it does and a pain to fix.

To Mike, I put my TRVs on horizontally to move the head as far away from the rad heat as possible in the hope that it would be more influenced by circulating air. Vertically mounted valves are less likely to be damaged however.

Also, as you have a combi, the towel rad won't come on with hot water demand only.

As others have said there should be no need for non-return valves.

Finally, I'd add an automatic bypass valve between flow & return unless your boiler has one built in.

[Mike Barnard]

And again, please excuse me not replying to individual posts, I repeat myself too often like that.

Thanks for the reviews. I know it's a simple terraced house, but I think we all agree that getting it right at the beginning saves lots of money and bother later.

Now, all I have to do is fit it. I'm goint to wait until monday to start the plumbing as my son will be at school and out of the way.

Cya.

[Mike Barnard]

Its a small house so vertically it will be. I do see the logic though.

No great problem, but it there a way to make that happen? Only by pushing the DHW through the rail I guess.

. .

Hmm, I do need one in. Thanks for that heads up. No one else spotted it. :) Now, where does it go on the plan?

[Mike Barnard]

From the Honeywell pdf for their valve...

"The DU145 should be fitted immediately after the pump between the flow and return. Pipework should be 22mm to accommodate maximum capacity and flow should be in the direction of the arrow marked on the body."

Thanks anyway.