M
mysteryman
It looks as if it is installed correctly as contraflow to me.
Connecting heat bank to boiler with plate heat exchanger?
- Thread starter Hedgehogboy919
- Start date
Sponsored Links
Hi Norcon and Agile. Yes I did it myself and yes you are right, I have connected both flows in the same direction! Thanks for pointing that out. The pump is flowing downwards which is correct but I need to swap over the CW mains connections to the PHE.
The tank has a port for the boiler flow at the top next to the port flow to the HW PHE. Another port at the bottom of the tank for boiler return. There are are 2 other ports for CH flow and return. I have uploaded a diagram of how I think it should work. Please take a look.
Will this work? If so, do you know if boiler will operate efficiently at optimum condensing temperature in this arrangement?
Are other items required to be fitted such as automatic air valves, non-return valves etc.?
The tank has a port for the boiler flow at the top next to the port flow to the HW PHE. Another port at the bottom of the tank for boiler return. There are are 2 other ports for CH flow and return. I have uploaded a diagram of how I think it should work. Please take a look.
Will this work? If so, do you know if boiler will operate efficiently at optimum condensing temperature in this arrangement?
Are other items required to be fitted such as automatic air valves, non-return valves etc.?
Use S plan or S plan+ if there is a third zone and ditch the mid position idea. All or nothing and the plate will certainly give you all and easier wiring.
I would use the ch flow port as the input. The return should be above the solar section but if no solar is being implemented now then connect to the lower tapping.
I would use the ch flow port as the input. The return should be above the solar section but if no solar is being implemented now then connect to the lower tapping.
Perhaps he recognised the advantages - such as decoupling the conflicting requirements of minimum flow through boiler vs variable flow through CH system with all TRVs and modulating pump ? I'm not surprised to see plumbers spouting unnecessary venom when a TS or HB is mentioned.
But back to the original query, I can't see what the problem is - what does the location/route of the radiator plumbing have to do with the boiler circuit ? I'm assuming there is a F&E tank somewhere (hopefully at the highest point of the system) - as long as this is high enough to give sufficient head for the boiler and not too high for the store and boiler pressure rating, then the CH connections are irrelevant to the boiler. All the boiler "sees" is the head from a F&E tank providing a head to a direct cylinder.
The return to the boiler can come from the bottom of the store (you'll want to move it up when you get the solar installed), the flow from the boiler goes into the top of the store. You'll need to modulate the flow rate, or the return temperature, so that the flow temperature is hot enough to heat the bank top-down - although your heat exchanger setup is poorly designed in that respect and will very quickly de-stratify your store. For my store, I used a TMV in the return line, mixing hot water from the boiler flow with cold from the store bottom - in my case I still have a non-condensing boiler and so wanted to avoid condensing. From an efficiency POV, you would want to keep the return to a condensing boiler as cool as possible and vary the flow rate to get the flow temperature you want - but obviously there are limits imposed by the design of the boiler.
Stratification is important - and also (in part) why I decided on a thermal store rather than heat bank for my flat. To get optimal results, you need (as someone pointed out) contra flows in the heat exchanger AND to match primary flow rate with DHW flow rate. If you can match the flow rates properly, you'll then be able to return cold water to the bottom of the store that is only a few degrees warmer than the incoming mains. The colder you can keep the bottom of the store, the more effect you'll get from your solar when the weather is marginal.
However, as you have it, your return will never be cooler than your DHW flow AND your primary flow rate will need to be at least as much as needed to satisfy your highest DHW flow rate - under any other conditions it will be higher than needed and primary return to the store will be hotter than necessary.
I would suggest you may find the folks over at the Navitron forum more welcoming - there are a few people here who cannot (or will not) accept that anything other than a combi boiler (or at a pinch an OV DHW cylinder) has any place for anyone or anywhere.
I wrote up my install in this thread and there's a schematic near the bottom of the first page. Apart from you having an external DHW heat exchanger instead of an internal coil I see no reason you can't do just the same.
I'd suggest going back to the boiler manufacturers and asking their recommendations for "heating an open vented thermal store - how would they recommend controlling the boiler loop flow temperature to ensure top down recovery ?"
Also, just looked up, I started a thread here where the subject of store stratification when using an external heat exchanger was discussed. You may find it interesting - or a laugh
Sponsored Links
Perhaps he recognised the advantages - such as decoupling the conflicting requirements of minimum flow through boiler vs variable flow through CH system with all TRVs and modulating pump ? I'm not surprised to see plumbers spouting unnecessary venom when a TS or HB is mentioned.
As I understand it, the boiler circuit has to be part of the CH. I don't want a FE tank or anything in the loft, so I intend to have a sealed CH system which requires an expansion vessel.
Yes there are dedicated ports for these on the HB.
Ok, now you're talking.
I assume you are referring to my diagram and not confusing the DHW side in the photo?
I have a TMV for this purpose but the company who I bought it from don't have a diagram, can you refer me to a diagram somewhere?
- in my case I still have a non-condensing boiler and so wanted to avoid condensing.
Yes this is one of my concerns and is this achievable when the boiler flow and return are just circulating through a PHE when only the HB needs charging?
Hang on, you are talking about the DHW side now, although I presume the same principle applies.
Well I remember reading somewhere a suggestion for using a TMV to somehow control the temperature of the return to the bottom of the HB from the DHW but again no diagram.
.
Ok I will try my luck with them. Thanks for your help.
I read your interesting article. I will need to study your sketch with fresh eyes next week.
Already asked them. They were helpful but said they don't provide system diagrams.
Also, just looked up, I started a thread here where the subject of store stratification when using an external heat exchanger was discussed. You may find it interesting - or a laugh
Read that too. V interesting but a bit over my head I'm afraid.
I'll get back to this next week. Thanks again.
OK, you'll already have a F&E tank somewhere - although looking again I see you've got one integrated into the top of the store. Where is this in relation to the rest of the CH ?
But the key thing you seem to have missed is that the CH does NOT have to come direct off the boiler - and there are some significant benefits by running it from the store instead (more if you had a condensing boiler).
The boiler needs a certain flow rate to avoid damage and/or safety issues.
Your central heating needs a different flow rate - significantly lower under light load conditions.
So running the CH off the boiler means compromises and what could be terms fudges. The most common of these is a bypass so you can feed hot water straight back into the boiler to keep the flow rate up. To make these work means a fixed speed pump, and that frequently leads to noisy radiator valves.
If you run the CH off the store, you can design the CH without compromising on the design to accommodate the boiler. In the flat I went fully TRV, no room stat, and a modulating pump. The CH turns on and off with the time clock, and the TRVs control the temperature in each room. There are no problems with balance - eg the living room is warm so the cold bedroom stays cold sort of thing. And the system is virtually silent because the modulating pump cuts back the pressure as the TRVs close.
I also used a TRV in the CH flow so that the flow (and hence rad) temperature would be largely independent of the store temperature.
<dons flameproof jacket and waits for the plumbers to light up>
Once you no longer have to consider the CH circuit, you can also design the boiler loop to suit the boiler. In my case, the boiler has a built in fixed speed pump, and I've just put a TMV in the return to regulate the temperature. You can see this on the diagram I linked to earlier, and in the photos in my article.
For a non-condensing boiler this should be set so the return is above that at which condensing is a risk, and adjusted to give the desired flow temperature - though your boiler may be able to modulate to set this for a given flow rate and return temp.
I was talking about the DHW side - someone else picked this up, I didn't notice it, but it looks like both the primary and DHW flows are downwards in the PHE. Ideally they should be opposite - probably make the DHW flow upwards and the primary flow downwards. Doen that way, and with the flows accurately matched to load, the return temp into the bottom of the store would be quite close to the incoming cold water supply temp.
Your diagram for the boiler loop does have the flows correct.
See the diagram I linked to. it's the three port valve linking boiler flow and return, and the store.
Bit confused here. My diagram shows my envisaged CH solution so the flow would be hot flow from PHE to top of store because the boiler is charging the store via the PHE. But the DHW from the store has to flow from the top (Hot) to bottom (cool) of the store because the store is heating the mains water. If I did as you suggest, it would mean the PHE being mounted above the height of the store which means air problems similar to what you described for the CH fix, or have I misunderstood?
OK, I can see there being problems getting the rads filled initially, but I can't really see why a loop of pipe going higher than the F&E tank should stop the system working. The pipes are sealed so will not admit air (if they did, then they'd have let water out normally) - they'll just be at a bit less head - about 25' absolute instead of 30' absolute.
Unless you planned to run the CH very hot, and hence the lower boiling point at the lower pressure would have an effect, then it's not going to be an issue once the system is filled. It really will NOT affect any other ports on the store, and you won't have air bubbling out of the F&E tank.
Once filled, the weight of water hanging down one leg of the syphon will balance the weight of water hanging in the other. It won't affect the pump, the boiler, the store, the rads - nothing.
The biggest problem I see is getting the system filled in the first place. If the pump is powerful enough then it should be able to pump water "over the top" and fill the system, but you'll be left either with air in the pipes, or with it being carried over and deposited in the rads. The only difference really is that you won't be able to use air vents (manual or automatic) in the loops to let the air out.
I'd be tempted to just plumb it up and try it.
I would give serious consideration to buying a standard F&E tank and putting it in the loft. It will be a LOT cheaper, and a LOT simpler than the messing around you are planning with PHEs and so on.
Is this because it would be a sealed system?
So if I put a F&E tank in the loft, it would not be a sealed system and then I would be able use auto air vents? And I would just use the integral F&E on top of the store to initially fill the store, or should I just fill the whole system from the F&E tank in the loft?
No, because they would be above the water level in the integral F&E tank. So rather than letting air out, they'd let air in.
You'd just disconnect the integral F&E tank and take the pipes up to the one in the loft. This only needs to be just higher than the pipes for air vents to work - there's an argument that manual vents might be better, automatic ones tend to stick and either leak (fail to close after venting) or not vent (fail to open) when they've been in and inactive for some time.
As I see it, a F&E tank will set you back some modest amount (£20-£30 complete with fittings ?). To connect your boiler and CH loops up, you'll just need a TMV for the boiler loop (I'm assuming you already have the pump), and a pump and TMV for the CH loop (though I'll admit a Grundfos AlphaII modulating pumps isn't cheap at around £100). You can of course just stick to having the CH off the boiler loop with a 3 port valve and not gain the benefits from running off the store.
To make your CH system into a sealed system you'll need the PHE (well over £100+), a second pump, and probably a couple of valves - plus the pressurisation stuff (expansion vessel with PRV, fill loop, etc). Then you'll have to keep an eye on the pressure and top it up from time to time as the air separates out or water escapes through any leaks (or the PRV which also tend to leak if disturbed).
Apart from being able to get a nice quiet fully-TRVd CH system, there is another advantage to having the CH run off the store. You have an immersion heater, and if the boiler breaks down then that can keep the heating going from it - although it's questionable how effective it will be if your load is large. I did some measurements in the flat after putting the store in, and it averaged about 2kW for heating and standing losses during last winter's cold spell - thus leaving enough capacity for a reasonable amount of hot water.
That's probably less of an issue with your oil boiler which is almost certainly more reliable than modern gas boilers - but I believe some people were running low on heating oil last December because the tankers weren't able to get out and resupply them.
Oh yes, one thing you will need to do, apologies if you've already thought about it ...
All that lot will need to be well insulated - including the store. The heat loss from all that exposed pipework etc, and the minimally lagged tank, will be horrendous. But if well lagged then you can get the losses right down.
I got the standing losses for my store down to about 80W. For comparison, the losses from the condensing gas combi boiler next door came in at about 160W with the "eco mode*" turned off.
On this boiler, ECO mode turns off the "fire up periodically to keep the DHW heat exchanger warm" function - without which it can take a long time to produce any hot water.
All that lot will need to be well insulated - including the store. The heat loss from all that exposed pipework etc, and the minimally lagged tank, will be horrendous. But if well lagged then you can get the losses right down.
I got the standing losses for my store down to about 80W. For comparison, the losses from the condensing gas combi boiler next door came in at about 160W with the "eco mode*" turned off.
On this boiler, ECO mode turns off the "fire up periodically to keep the DHW heat exchanger warm" function - without which it can take a long time to produce any hot water.
.
I already have a spare TMV and a Wiflow pump. I presume the Grundfos somehow regulates flow, is it really important?
Did you see my reply about the DHW flow? I might be attacking it this weekend so be nice to get it right as I have already changed the arrangement once.
Do you mind me asking, are you some kind of an engineer?
I am going to make a diagram based on your very helpful info and put a diagram together and see if you agree. Cheers.
It depends on what you are going to do. I chose it because it will regulate the flow right down to zero - and it backs off both the power it used, and the pressure in response. What this means is that you can fit TRVs to every radiator without a bypass and without the system getting noisy. If you try that with a fixed speed pump, then at low flow rates the pressure rises and the valves get noisy.
There's information at
http://www.grundfos.com/products/find-product/alpha2.html
and
http://net.grundfos.com/doc/webnet/poweredby/gb/why_alpha2.html
As I said, they aren't cheap but I'm glad I went that route.
If you run the CH off the store like that, then you do away with the room stat, and all the compromises that go with it. The TRVs take care of room temps, and the boiler only runs when the store thermostat calls on it to top up the store.
It looks like both the primary and DHW flows are downwards. You want one up and one down. Partly because that's the logical way to do it, the DPS heatbanks pump the primary flow downwards, and then that sets the DHW flow rate as being upwards. It doesn't matter which goes up and whch goes down as long as they go opposite directions.
There is a very simple diagram showing the difference at the top of this article under the heading Flow arrangement.
I have no qualifications specific to plumbing or heating systems, but I do in other areas. I do have a certain amount of DIY experience with plumbing/heating.
That would be a good idea. Drawing a diagram will also help you get your ideas together - more than once I've had a great idea and then I drew it out and found that perhaps it wasn't so good after all
OK, a couple of diagrams for you to ponder over.
First off, this is a general arrangement as I'd do it - but not including any controls over DHW PHE primary flow as yet - and I've also omitted the F&E tank for clarity. The colour should give you an indication of the sort of heat profile you should normally be trying to achieve in the store to maximise the ability to use the solar panel input (not shown).
This differs slightly from the earlier schematic as it shows the TMV in the boiler loop as a diverter rather than mixer. In this mode, the TMV senses the flow temperature, and divert some (or all) of it to the top of the store when it's hot enough - and the rest back to the boiler return.
The key difference here is that you are controlling the flow temperature while the return is "what it ends up at", while a mixer controls the return temperature and the flow becomes "what it ends up at". There are pro's and cons both ways.
The divert arrangement will give you better control over store temperature. The main downside is you only have indirect control over boiler return temp and in particular you cannot quite guarantee not to go cold enough to avoid condensing. You would normally set the boiler on max, and rely on setting the flow to give the delta-T you want and hence the return temperature. In practical terms, for a given flow rate and a given boiler output, you will get a constant delta-T.
The mixing arrangement means you can control the return temp and thus avoid condensing. The downside is you have only indirect control over flow temperature. You can however take advantage of a modulating boiler and let it give some control over flow temp.
I chose the mixing arrangement for my current setup (non-condensing boiler) - I'd choose a divert arrangement with a condensing boiler. I actually have a couple more ideas, but I'll leave them out.
A secondary consideration is that in mixer mode, it should be within the range of a relatively cheap TMV sold for tempering DHW supplies - I picked some up off an "online auction site". In divert mode, you'll need a different valve as this would normally be well above the range of a DHW TMV.
The CH system should be fairly self explanatory.
On the next I've shown a couple of ideas for controlling primary flow in the DHW PHE.
On the left I've got it throttling the flow based on the PHE outlet temp. It will still heat the DHW up to near store temp, so you still need the TMV on that side as well.
How it should work is that the flow will be controlled so that as the DHW flow rate varies, and hence the cooling effect on the primary, the valve will adjust the flow rate to suit. I'd be looking to set it a little above the prevailing cold water supply temp - I'd guess 10˚C higher would be a reasonable starting point and experiment from there. You may need a bypass round the pump to avoid dead-heading it at very low DHW flow rates.
Note that the sensor bulb ideally needs to be inside the PHE port so that it can sense the temperature even if the valve has fully shut and there is now flow - otherwise you could find a situation where the DHW goes cold until the pipes lose a bit of heat and the valve starts allowing some flow.
On the right is an arrangement where the primary flow rate is controlled from the DHW flow temperature. It will only admit as much primary flow as is required to heat the DHW to setpoint.
Note that neither of these is a good solution from a control engineering POV. Controlling PHEs by varying flow rate is very difficult to do accurately and stably so it's generally avoided if possible. Normally you would aim to keep the primary flow rate high and vary the loop temperature as this gives good control - which is the starting point in the thread I linked to earlier. Because the temperature differential between primary input and secondary (DHW) output tends to be quite small if you keep the primary flow rate high, you can in fact get quite good control of secondary (DHW) temperature by only controlling primary loop temperature - thus eliminating the TMV in the DHW side.
That's the arrangement in teh diagram here if you imagine the lower PHE isn't there.
With a single PHE though, this means the primary water you return to the store will be quite warm (or even hot) most of the time - although at a much lower flow rate than with an uncontrolled flow.
This is one reason I went with a thermal store rather than heat bank in the flat.
First off, this is a general arrangement as I'd do it - but not including any controls over DHW PHE primary flow as yet - and I've also omitted the F&E tank for clarity. The colour should give you an indication of the sort of heat profile you should normally be trying to achieve in the store to maximise the ability to use the solar panel input (not shown).
The key difference here is that you are controlling the flow temperature while the return is "what it ends up at", while a mixer controls the return temperature and the flow becomes "what it ends up at". There are pro's and cons both ways.
The divert arrangement will give you better control over store temperature. The main downside is you only have indirect control over boiler return temp and in particular you cannot quite guarantee not to go cold enough to avoid condensing. You would normally set the boiler on max, and rely on setting the flow to give the delta-T you want and hence the return temperature. In practical terms, for a given flow rate and a given boiler output, you will get a constant delta-T.
The mixing arrangement means you can control the return temp and thus avoid condensing. The downside is you have only indirect control over flow temperature. You can however take advantage of a modulating boiler and let it give some control over flow temp.
I chose the mixing arrangement for my current setup (non-condensing boiler) - I'd choose a divert arrangement with a condensing boiler. I actually have a couple more ideas, but I'll leave them out.
A secondary consideration is that in mixer mode, it should be within the range of a relatively cheap TMV sold for tempering DHW supplies - I picked some up off an "online auction site". In divert mode, you'll need a different valve as this would normally be well above the range of a DHW TMV.
The CH system should be fairly self explanatory.
On the next I've shown a couple of ideas for controlling primary flow in the DHW PHE.
How it should work is that the flow will be controlled so that as the DHW flow rate varies, and hence the cooling effect on the primary, the valve will adjust the flow rate to suit. I'd be looking to set it a little above the prevailing cold water supply temp - I'd guess 10˚C higher would be a reasonable starting point and experiment from there. You may need a bypass round the pump to avoid dead-heading it at very low DHW flow rates.
Note that the sensor bulb ideally needs to be inside the PHE port so that it can sense the temperature even if the valve has fully shut and there is now flow - otherwise you could find a situation where the DHW goes cold until the pipes lose a bit of heat and the valve starts allowing some flow.
On the right is an arrangement where the primary flow rate is controlled from the DHW flow temperature. It will only admit as much primary flow as is required to heat the DHW to setpoint.
Note that neither of these is a good solution from a control engineering POV. Controlling PHEs by varying flow rate is very difficult to do accurately and stably so it's generally avoided if possible. Normally you would aim to keep the primary flow rate high and vary the loop temperature as this gives good control - which is the starting point in the thread I linked to earlier. Because the temperature differential between primary input and secondary (DHW) output tends to be quite small if you keep the primary flow rate high, you can in fact get quite good control of secondary (DHW) temperature by only controlling primary loop temperature - thus eliminating the TMV in the DHW side.
That's the arrangement in teh diagram here if you imagine the lower PHE isn't there.
With a single PHE though, this means the primary water you return to the store will be quite warm (or even hot) most of the time - although at a much lower flow rate than with an uncontrolled flow.
This is one reason I went with a thermal store rather than heat bank in the flat.
After a little more thought, but drifting off topic a bit for the OP, this is how I'd probably connect a condensing boiler.
With boiler set on max, the thermostatic valve will regulate flow so maintain desired store reheat temperature.
From cold startup, the automatic bypass allows just the minimum flow for the boiler to operate safely. Once the thermostatic valve is opening, the differential pressure will drop and the bypass will close. The return flow to the boiler is as cold as is practical thus extracting the max amount of heat from the gas exhaust.
From cold startup, the automatic bypass allows just the minimum flow for the boiler to operate safely. Once the thermostatic valve is opening, the differential pressure will drop and the bypass will close. The return flow to the boiler is as cold as is practical thus extracting the max amount of heat from the gas exhaust.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
