magnaclean filter and low loss header

[doitall]

This system has already been discussed on this thread....

//www.diynot.com/forums/viewtopic.php?t=239878&postdays=0&postorder=asc&start=0[/QUOTE]

Thank you Norcon, never saw that thread, or I would have joined in.

 

[Norcon]

Looneyfitter has a nice picture on page 5 I think you'll like.

 

[doitall]

Looneyfitter has a nice picture on page 5 I think you'll like.

I will have a browse later.

 

[ajrobb]

First, thank you all for your time.

The property is an L shaped chalet bungalow style 120m² down and 40m² up. Boiler size calculator suggests 44-48 kW. 50,000 kWh/year (52,000 in the last 12 months).

HWC: 300 litre unvented Flomaster Titan indirect

Radiators:

Location Type Height Length
Hall K2 450 1000
Hall KP 450 1200
Lounge P2 500 1750
Lounge K2 600 1500
Dining KP 500 1730
Kitchen K2 700 900
Laundry K1 450 1000
Music K2 450 1400
WC K1 450 500
Back K2 600 1800
Office K2 450 900
Landing P1 540 1750
Bed 1 K2 450 900
Bed 1 P1 540 1150
Bed 2 K2 450 1100
Bed 3 P1 540 1560
Bed 3 P1 540 850
Bed 4 K2 700 800
WC K1 450 480

As far as I can make out, these are way too small for 44-48 kW (unless I crank the flow temperature up to max).

The circulating pump in a Grundfos UPS 15-60

The gate valve connects the pump inlet to the common return.

Circulation through the radiators is limited by their balance and is adequate on all radiators either for 11°C or 20°C temperature drop.

Given that the boilers modulate their pumps, I suspect an ABV between the circulating pump inlet and common return could help. It would boost the circulating pump at all loads, be more restrictive at low loads yet less restrictive (open up) at high loads (compared to a fixed gate valve). This could increase the temperature rise across the heat exchangers at low loads yet keep it from being excessive at high loads.

I'm not sure that I can make significant condensing savings as the house was cold when I balanced the radiators at 20°C temperature drop (70-50). I've gone back to 11°C. Without separate flow controls for CH and DHW, I can't even drop the CH flow temperature in mild weather.

The main savings I hope to make are keeping these old boilers going as long as pos. I have seen recommendations for filters improving reliability.

 

[doitall]

The radiator size don't make sense, what brand are they.

The gate valve is wrong, end off.

To get a good balance and flow the pipes have to be correctly sized, I suspect that may not be the case.

The boilers are struggling to get the heat away ( undersized pipes again) and the gate valve is causing the system to short circuit.

What size are the primary pipes from the boiler.

Have browsed through the other thread, the posters I count as good, have said the same as I'm saying now, (lucky)

However in my opinion the system has been designed/sized to have a stand-by boiler, and only one should be running with a changeover every 4 weeks or so.

I would therefor shut one boiler down and try it with the gate valve nearly closed, until an ABV can be fitted as a replacement.

I would also get rid of the system pump, if the pipes are sized properly.

 

[GaytonTonner]

However in my opinion the system has been designed/sized to have a stand-by boiler, and only one should be running with a changeover every 4 weeks or so.

That is my view. This is a bungalow. Is one boiler big enough to heat the whole house? If so then only use one.

I would therefor shut one boiler down and try it with the gate valve nearly closed, until an ABV can be fitted as a replacement.

I would also get rid of the system pump, if the pipes are sized properly.

I would go along with that. My suggestion of a installing a blending valve on the return stands, as it will protect the flaky heat X. He has gone through two so far. Getting the pipework right will mean he will have two reliable boilers.

As I now know the rads have TRVs on them I would also fit an A by-pass valve as well. The OP's concerns that a a blending valve would restrict flow is unfounded. Assuming the TRVs are all open full. The blending valve will ensure full flow back to the boiler at all times. Now, as TRVs are fitted, if the TRVs close up an Auto by-pass valve should be be between the rads/cylinder circuits and the blending valve, to ensure full flow.

Now assuming one boiler can do all the house. All he needs to do is.

1. Fit the blending valve
2. Fit the auto by-pass valve
3. Re-jig some piping.

If the two boilers are needed as one is not big enough. A cheap way is if he he does this.

Fit a small buffer cylinder. This can be a small, direct unvented cylinder of 80 to 100 litres, with 1" connections. The two 22mm boiler connections go to the draw-off with a 1" tee fitted here. The returns to the cold free with again a 1" tee. The cylinder stat controls the boilers. They only heat the cylinder. Off the others side of the cylinder a flow and return pipe can be fitted to the CH/cylinder circuits.

The cylinder acts like a cheap header and is controlled by this header. An Alpha variable speed pump can be fitted on the CH/DHW cylinder side. Then the room wall stat can be removed and TRVs all around.

No G3 as only system water is in the system. A larger or additional expansion vessel may be required as the water volume is now larger.

a) The boilers heat only the buffer cylinder and happily have full flow at all times.
b) The CH circuit can take out of the buffer as much or as little Kw as needed to heat the house. The DHW can take full flow. Once 1.3 of the heat has been extracted the two boilers cut in. Two stats could be fitted on the buffer cylinder to prevent boiler cycling. No boiler sequencing is needed. One boiler can be on rest in summer.

Cheap and easy and highly effective.

 

[doitall]

Good post GT, in my opinion slightly over the top perhaps, and I think blenders would be too restrictive.

There is the potential for problems, and perhaps why the HX keep going if one looks closely.

I mentioned several times about the gate valve and also the primary pump in the system flow being wrong, sorry I didn't say why.

Look at the pic, and think boiler pump speed modulates right down as the OP rightly said.

Next look at the short circuit between the return, through the gate valve and back into the pump which is still running at full speed.

One has to assume now because we don't know, but if the much stronger pump is full speed and pinching all the return water, (being the easiest road) perhaps it can also stall the boiler pumps running on low speed.

 

[GaytonTonner]

Good post GT, in my opinion slightly over the top perhaps, and I think blenders would be too restrictive.

There is the potential for problems, and perhaps why the HX keep going if one looks closely.

I mentioned several times about the gate valve and also the primary pump in the system flow being wrong, sorry I didn't say why.

Look at the pic, and think boiler pump speed modulates right down as the OP rightly said.

Next look at the short circuit between the return, through the gate valve and back into the pump which is still running at full speed.

One has to assume now because we don't know, but if the much stronger pump is full speed and pinching all the return water, (being the easiest road) perhaps it can also stall the boiler pumps running on low speed.

The OP hasn't give us the heat requirements of the house and the boiler size.

My first suggestion was
-----------------
My suggestion of a installing a blending valve on the return stands, as it will protect the flaky heat X. He has gone through two so far. Getting the pipework right will mean he will have two reliable boilers.

As I now know the rads have TRVs on them I would also fit an A by-pass valve as well. The OP's concerns that a a blending valve would restrict flow is unfounded. Assuming the TRVs are all open full. The blending valve will ensure full flow back to the boiler at all times. Now, as TRVs are fitted, if the TRVs close up an Auto by-pass valve should be be between the rads/cylinder circuits and the blending valve, to ensure full flow.

Now assuming one boiler can do all the house. All he needs to do is.

1. Fit the blending valve
2. Fit the auto by-pass valve
3. Re-jig some piping.
-------------------

That still stands. You size the blending valve to suit, which may means a 28mm on 22mm pipe. The blending valve does give full back to the boilers. I did say get rid of the third full speed pump.

The suggestion of a cheap header using a small, direct, unvented cylinder is not over the top. It will solve all the problems and add value in TRVs all around if wanted. OK a new cheap Wilo Smart pump may be needed, which is also cheap. No potential problematic auto by-pass valves are needed.

Once pipes get above 28mm the prices shoot up. Large bore headers are very expensive, so a cheap, small, direct, cylinder can be a far better option - and pre-lagged as well. It provides a superb buffer. The buffer isolates the heat generators from the system. The system can trickle out heat from the buffer, If the CH only needs 1kW of heat, then it gets it and no interference with the boilers.

I have used a cheap unvented cylinder in the past to do exactly this in a small hotel. They were short of cash, and so was I and needed the work. It worked superbly, was very cheap to using commercial big headers and no complex, expensive boiler sequencing controls. I have not had a call back and that was 8 years ago.

The buffer can act as a sludge gatherer, as poorly installed thermal stores can. A Spirotech filter was fitted on the system return to the buffer to gather any crap. The system was sealed, so little chance of heavy sludge. The unvented cylinder pressure/temp relief controls were left in place just in case. The boilers both had PRVs, anyhow. No G3 needed to fit the buffer. Two cheap boilers were fitted. I sourced two cheap combis on a deal and never connected up the DHW. An extra expansion vessels was needed to supplement the two vessels on the boilers.

The rads were zoned with a Smart pump and check valve to each. A timer switched off the pump to each zone which had TRVs on all room rads.

It was all cheapish domestic stuff, apart from the TRVs in a commercial application.

 

[Agile]

I am also a little confused by the heat loss being quoted as 48 kW.

That comes to 300w per sq m. which seems very high !

Typical UFH systems give 100-150w psm so your heat loss seems to be three times a well insulated property.

As a very rough rule of thumb 1 kW per sq m is a very easy way to roughly assess the heat requirements of a property adjusted upwards if not so well insulated.

I am also rather concerned that you seem to want to run two boilers modulated back rather than sequencing them as the demand reduces.

Tony

 

[doitall]

GT, I wasn't disagreeing about the buffer tank, just the bender valve, it isn't needed.

An AVDO in the by-pass would close the short circuit and ensure there's a full flow through both boilers, see drawing. and actually improve circulation with all 3 pumps doing the same job, instead of working against each other'

Comment welcome.


View media item 29614

 

[ajrobb]

We moved in with a single 25 kW boiler and that is simply not enough. If I wanted to throw £60,000+ at the property, I'd replace the roof, insulate the inaccessible voids, insulate under the floor, rewire and re-plumb and never see a return.

With TRVs in 1/2 rooms turned down to 10-15°C, the radiators were consuming 31 kW gas with the boiler temps turned up for cold weather and cycling on the room stat. I've turned the boilers back down to 70°C for milder weather. I can see that both boilers should be pumping in parallel into a large diameter LLH rather than squeezing through a single 22mm gate valve (albeit wide open). That way, the boilers can modulate their individual pumps without a danger of stalling.

If I turn one boiler off, it seems to have problems starting up again. I have seen one graph showing boilers are a couple of percent more efficient at 15-30% load than at 100%. So there seems to be little benefit in sequencing single boilers.

If I convert to a proper LLH, I was wondering about using something like an ABV on the individual boiler flows to give a constant pressure drop between the flow and the LLH to reduce the flow through each HX, otherwise I think the temperature rise across each HX will be minimal and there will be no chance of condensing with a flow temperature of 70°C. (I suspect the boiler pump modulation is designed to work against an ABV anyway.)

 

[doitall]

I think you're missing the point, you don't need to chuck large sums of money at it, there is nothing wrong with the design as is, other than I would increase the header pipe size to 42mm given that you want both boilers running.

As the drawing shows, the larger pump is stalling the boiler pumps when they modulate down, which is what I said at the start of this thread. All the time the gate valve is in the by-pass it will never be any different.

You could turn it off for 10 mins and see the difference it makes.

 

[ajrobb]

As the drawing shows, the larger pump is stalling the boiler pumps when they modulate down

I can see where you are going with the drawing but, consider if you close the gate valve, the circulation pump will be pumping in series with the boiler pumps and assisting rather than stalling. Opening the gate valve won't magically stall the boiler pumps but simply reduce the assistance.

BTW, I think all three pumps might be similar or even the same.

If I close the gate valve, the boilers shut down with insufficient flow.

 

[doitall]

As the drawing shows, the larger pump is stalling the boiler pumps when they modulate down

I can see where you are going with the drawing but, consider if you close the gate valve, the circulation pump will be pumping in series with the boiler pumps and assisting rather than stalling. Opening the gate valve won't magically stall the boiler pumps but simply reduce the assistance.

BTW, I think all three pumps might be similar or even the same.

Lets assume all three pumps are the same duty, the only difference is 2 modulate down therefore reducing the duty.

Next you have one pump on the flow (positive head) and 2 on the return (negative head) the larger head is going to pull the return, at least enough to reduce the flow through the boilers pumps.

The problem is common with larger system and different head pumps, and one reason why you need the large header, you will also see check valves on the smaller pumps for the same reason.

To conclude, all the time there's an open circuit between the flow and return, the system pump will pull the boiler return and slow the flow through the boilers at best.

Any industrial/commercial heating guy will tell you the same thing.

Edit, I forgot to say that even if all 3 pumps are the same duty, the system pump will always be the stronger because the other two have the resistance through the boilers to overcome first.

 

[ajrobb]

even if all 3 pumps are the same duty, the system pump will always be the stronger because the other two have the resistance through the boilers to overcome first

Given that the boilers shut down if I close the gate valve and run with only max 8°C temperature rise if I open it wide, I am sure that both boiler pumps in parallel push much more water round the primary circuit than the circulation pump pushes through the rads. Even at part load, the gate valve stays at flow temperature so is not taking reverse return flow. Also, the temperature drop across the rads is greater than the temperature rise across the boilers. Finally, the flow temperature through the circulation pump to the rads is the same as the flow temperatures from the boilers so there cannot be reverse return flow through the gate valve.