Thermal Store Issues

[joeirish]

I have a system that I had installed four years ago when we built our house. It is near passive spec. The system has recently has being causing issues. Hopefully others will be able to understand my description of the system and the issue..

 

Essentially I have thermal store that is heated either by PV powered immersion and/or condensing oil boiler. I have UFH and wet towel rail and skirting rads (never used) upstairs. The way the system was installed is similar to others described here, PV heats thermal store for DHW and the boiler mainly heats the UFH. I had always assumed that the boiler would heat the thermal store (there is a flow and return to the thermal store from the boiler) and that the UFH and DHW would draw from this. The installer has taken spurs off the pipes to and from the boiler and connected these to the UFH manifold. Each time the ufh comes on the boiler fires up for a while. So essentially the ufh circuit goes from the house to the boiler outside and then back again. It was when the boiler stopped working a couple of weeks ago even that I suspected there might be a problem. What happened was that even though the thermal store was quite hot (70 at the top and 55 lower down) I was only getting cold water circulating round the ufh! It looks like the ufh circuit is actually not flowing via the thermal store at all but just via the boiler.

 

The boiler is now fixed and once again I have the situation where my ufh is really working like large rads, the floor gets quite warm when the ufh pump is on and then gradually cools once the timer turns off the ufh pump. It would seem that the high temperature from the boiler flow 

My ideal design was that the TS heats up using either the PV powered immersion or the boiler and then the heat from this is used for UFH and DHW. Only if the TS drops below a certain temperature does the boiler fire up. So is it possible to have such a system?

Unfortunately the installer is not around any more to help.

Edited May 2, 2019 by joeirish
typo

[PeterW]

@joeirish Yes ... I think ..!

 

You need a zone valve in the flow from the boiler that is only energised when the boiler is firing. Done correctly, the boiler trigger should switch the zone valve on, and the micro switch on the valve should then trigger the boiler. 

 

This would mean that the UFH would draw from the TS first, and then the TS stat would trigger the boiler valve, which would trigger the boiler. 

 

I would put this as reasonably close to the boiler as possible, and put it in the flow pipe. This means that cabling changes are reduced. 

 

Two questions though :

- does the TS have a stat on it and how high up..?

- does the UFH manifold have a blender and pump..?

 

Both answers will help confirm the options. 

[joeirish]

Thanks for that. In answer to your questions, the TS has two sensors that measure the temp up high and further down. The is a stat valve on the manifold is that what you mean? There is also a pump on the ufh manifold. I've attached a photo of the set up. The two grey lagged pipes on the left are the flow and return from the boiler. You can just make out the spurs going to and from the manifold. The mixer valve is on the top left and the pump is the green device. The red dial controls the pump speed.

Edited May 2, 2019 by joeirish
typo

[PeterW]

Looks like a standard manifold but it does make me wonder why the manifold is pulling from the TS if it’s next to the manifold or is that not what is to the left ..?

[Temp]

1 hour ago, joeirish said:

The installer has taken spurs off the pipes to and from the boiler and connected these to the UFH manifold. Each time the ufh comes on the boiler fires up for a while.

 

There are several different types of TS and different ways to set them up but that sounds wrong to me. I would expect the UFH to be connected to the secondary side of the TS not the primary.

 

That said perhaps the connection to the store is bidirectional. eg The same pipe into the store is used to send water from the boiler to the TS and UFH can draw water back out of the TS when the boiler is off? Seems an odd arrangement to me.

 

1 hour ago, joeirish said:

My ideal design was that the TS heats up using either the PV powered immersion or the boiler and then the heat from this is used for UFH and DHW. Only if the TS drops below a certain temperature does the boiler fire up. So is it possible to have such a system?

 

Our system does work the way you expected. The boiler heats the TS (primary circuit) and the TS heats the UFH/DHW (secondary circuit). The two circuits are totally independent except for the master electric switch. So the room stats control the UFH manifold and pump which draws heat from the TS but the boiler only fires up when the temperature of the TS falls far enough to trigger the TS stat.

 

 

 

[pulhamdown]

1 hour ago, joeirish said:

 

My ideal design was that the TS heats up using either the PV powered immersion or the boiler and then the heat from this is used for UFH and DHW. Only if the TS drops below a certain temperature does the boiler fire up. So is it possible to have such a system?

 

 

Yes, it is.  That's how our system works.  Our UFH takes hot water from the middle of the thermal store, mixes with cold, and returns it to the bottom.  No spurs off between the TS and the boiler.  The boiler only kicks in when the temperature at the top of the boiler drops below the set level. 

[joeirish]

1 hour ago, PeterW said:

Looks like a standard manifold but it does make me wonder why the manifold is pulling from the TS if it’s next to the manifold or is that not what is to the left ..?

That is the TS on the left. But when the UFH pumps starts up it circulates the UFH fluid first to the boiler (which is about 5 metres away and outside the house in an external casing). On the occasions when the boiler would not fire up the UFH just had cold fluid circulating even though the TS was hot. I only became aware of this recently when the boiler stopped working.

[joeirish]

52 minutes ago, pulhamdown said:

 

Yes, it is.  That's how our system works.  Our UFH takes hot water from the middle of the thermal store, mixes with cold, and returns it to the bottom.  No spurs off between the TS and the boiler.  The boiler only kicks in when the temperature at the top of the boiler drops below the set level. 

Thanks for that. So it is possible to have that type of set up. The question is now how to achieve this. I have had the original installation guide from Latento who made the TS. And essentially with this type of set up the boiler provides the heat for the UFH and the TS is used just for the DHW. Not what I wanted though. So now I'm trying to find out the best way to make the system do what I intended.

[joeirish]

56 minutes ago, Temp said:

 

There are several different types of TS and different ways to set them up but that sounds wrong to me. I would expect the UFH to be connected to the secondary side of the TS not the primary.

 

That said perhaps the connection to the store is bidirectional. eg The same pipe into the store is used to send water from the boiler to the TS and UFH can draw water back out of the TS when the boiler is off? Seems an odd arrangement to me.

 

 

Our system does work the way you expected. The boiler heats the TS (primary circuit) and the TS heats the UFH/DHW (secondary circuit). The two circuits are totally independent except for the master electric switch. So the room stats control the UFH manifold and pump which draws heat from the TS but the boiler only fires up when the temperature of the TS falls far enough to trigger the TS stat.

 

 

 

So I have to figure a way of getting two independent circuits. That's the question. I'll have to see if Peter's idea would do this by having a zone valve would do this.

[joeirish]

1 hour ago, PeterW said:

@joeirish Yes ... I think ..!

 

You need a zone valve in the flow from the boiler that is only energised when the boiler is firing. Done correctly, the boiler trigger should switch the zone valve on, and the micro switch on the valve should then trigger the boiler. 

 

This would mean that the UFH would draw from the TS first, and then the TS stat would trigger the boiler valve, which would trigger the boiler. 

 

I would put this as reasonably close to the boiler as possible, and put it in the flow pipe. This means that cabling changes are reduced. 

 

I've been trying to get my head around this. Excuse the beginner's questions but what do you mean by the zone valve being energised? Any links to wiring diagrams etc. Thanks

[ProDave]

Reading this I think you need some plumbing alterations AND some wiring alterations.

 

Every TS system I have been involved in draws hot water from the TS to drive the heating (whatever form that takes radiators or UFH).  The heating is usually via 2 port valves and conventional time clocks and thermostats to say when the heating is on or off.

 

then QUITE SEPARATE to that, the boiler will fire up driven by the tank thermostat to heat the TS to desired temperature.  That can also be under the control of a time clock if you want (i.e often the "Hot Water" side of a normal dual channel time clock)

 

Separate issue, the UFH manifold should regulate the temperature to the UFH pipes. If your UFH is running too hot check that is set up properly and the corect low temperature is set on the manifold blending valve.

[newhome]

1 hour ago, ProDave said:

then QUITE SEPARATE to that, the boiler will fire up driven by the tank thermostat to heat the TS to desired temperature.  That can also be under the control of a time clock if you want (i.e often the "Hot Water" side of a normal dual channel time clock)

 

 

My boiler only fires if the UFH calls for heat and the TS isn’t at the desired temperature. Or as you say when the DHW time clock is set. 

 

[PeterW]

4 hours ago, joeirish said:

I've been trying to get my head around this. Excuse the beginner's questions but what do you mean by the zone valve being energised? Any links to wiring diagrams etc. Thanks

 

Ok 

 

Zone Valve or 2 port valve has a microswitch in it. When the valve is fully open, the micro switch closes, which would either give 230v to the boiler to fire, or close a set of no volt contacts on the boiler. 

 

Currently, your boiler fires when the time clock is set to on, and the thermostat on the TS calls for heat. 

 

New setup, you put the 2 port (closed) valve in the flow from the boiler, and the live feed to this is taken from the boiler switch wiring - ie what would normally make the boiler go live. 

 

Now when TS and time clock call for heat, the motor on the valve is energized, the valve opens and when it’s fully open, the micro switch triggers the boiler. This means the boiler pump isn’t pushing against a closed valve, and also stops a route for the UFH to try and circulate cold water through the boiler and into the manifold. 

 

Is there a gate valve near the boiler ..? If so, you could close this to simulate the zone valve being closed and then see if the UFH pulls hot water from the TS. 

 

 

[joeirish]

PeterW

 

Thanks for that explanation. Beginning to be clearer now. I can't see a gate valve on the flow but there does seem to be some sort of isolating val  either side of the boiler pump. I'm attaching a couple of photos. First shows the pump and the two valves. The second shows the top of the boiler cabinet. The lower pipe is labelled "Heating Flow" and has the sensor from the control unit attached by the cable ties.

[scottishjohn]

1 hour ago, joeirish said:

PeterW

 

Thanks for that explanation. Beginning to be clearer now. I can't see a gate valve on the flow but there does seem to be some sort of isolating val  either side of the boiler pump. I'm attaching a couple of photos. First shows the pump and the two valves. The second shows the top of the boiler cabinet. The lower pipe is labelled "Heating Flow" and has the sensor from the control unit attached by the cable ties.

the sensor at bottom of picture should have insulation round it so it gets correct temp transferred from pipe 

also if possible ALL those pipes should be lagged to stop heat loss ,which wil lower the effiency of your system 

[joeirish]

3 minutes ago, scottishjohn said:

the sensor at bottom of picture should have insulation round it so it gets correct temp transferred from pipe 

also if possible ALL those pipes should be lagged to stop heat loss ,which wil lower the effiency of your system 

I uncovered everything for the photo. These pipes on the top are usually covered with a layer of insulation. The ones by the pump are in an insulated area, the outer insulated casing has been removed. Do you think they need lagging as well as this.

Edited May 2, 2019 by joeirish