Wet UFH Plumbing & Wiring

[RHayes]

@vala

The Thermosense device originaly mentioned by PeterW is the programmer for yhe temperature sensor, be it a thermistor or other type of sensor probe.  A dry pocket (or a bit of 10mm copper pipe squashed and soldered at one end as i have done) would be needed to insert the probe in to amd then wire the probe back to programmer/controller for the temperature input.  setting the controller to a high histerisis so that the boiler only comes on when the tank drops below 40 degrees and then turns off whenthe tank reaches 60 degrees.  This way only one controller is and sensor/thermistor is needed and the wiring is straightforward.

 

If you want to use the principle of two tank stats one at 1/3 and one at 2/3 of tank height then you will need 2 controllers, 2 thermistors and still need the relay set up.  In this set up you wouldn't need the 10 degree histeresis and so would just set the bottom contorller at 60 or 70 degrees and the top controller at 40 degrees so that the boiler only ran when needed.  there is not realy any difference in this set up whether you go for the original buffer tank stats you were concidering or the Thermosense controllers.  I would also guess that the Thermosense controllers and acompanying thermistor/probe is more expensive than the original buffer tank stat you had in mind.

 

I'm happy to do a wiring diagram for you, just need to know whether you'd like to use 1 or 2 points of tempertaure measurment and whether you want to revert to the original buffer tank stat or the Thermosense controller and sensor probe.

 

Trust this helps explain the differences and the benifits of 1 point of measurement or 2 points of measurement at 1/3 and 2/3.

 

LMK your thoughts.

[vala]

@RHayes

Thank you for your offer.

From how I've understood it then, having 2 stats at 1/3 and 2/3 of the tank height would most likely have the boiler running less frequently compared to 1 stat as the temperature is measured at 2 points??

Do you think there would be much difference in the frequency of the boiler firing up between the 2 options?

The buffer vessel I'm going for from Newark Cylinders is 800mm in height so the difference between the 2 stat locations will be approx 266mm. Would the difference between the 2 water temperatures here be worth the extra stat, accompanying controller and extra wiring, vs a single stat?

[RHayes]

Hello Vala

 

You mentioned in your initial post that you had in mind to get a 100l vessell therefore the difference between the two sensors will be approximately 33 litres.  This could always be increased by moving the sensors further apart, for example 1/4 and 3/4 of the tank height.  I don't have any experiance in the placement of these sensors, however I guess an influencing factor would be what the output of your boiler is rated at compared to the total load of your underfloor heating.  Perhaps you can confirm.

 

We are getting in to thermodynamics and comparing load to demand with different flow temperatures between them too, but assuming it is something like a 30kW boiler and a 20kW underfloor heating load then the boiler will probably cycle on for about 3 or 4 minutes and off for about 5 or 6 minutes.  This is assuming the underfloor heating is all but on full demand.  If it is only a few areas that are heating then it may be a cycle of more like 1 or 2 minutes and off for about 10 minutes.

 

Not sure that this answers your question, however to reiterate the difference between the two options, with 1 stat you'll have just the 1 controller and sensor.  With the 2 stats, you'll have the 2 stats or sensors, 2 relays, and a box to house these relays in.  You can buy relays for £8-£10 each (you'd need 2) and an enclosure which i guess could be just a double back box and blank plate to house the relays in.  The only extra 1st fix wiring for the 2 stat option is a permanent live and neutral (terminal 1 & 2) to the BS location on the latest schematic and then just a case of connecting them up in the right order.

Edited September 20, 2021 by RHayes

[RHayes]

 

This is a rather rough sketch i have done in paint of how you would connect the stats and relays in the 2 stat option.  Trust you can make head or tail of it.

 

It is important that the stats are placed in the tank between the connections to the boiler and the underfloor heating connections.  I beleive it is also important that the flow from the boiler enters the top of the tank and return from the bottom.  Likewise the underfloor heating is fed from the top of the tank and returns to the bottom.

 

[RHayes]

@vala

I should have @ tagged you to the last to messages and now can't edit them.  Let me know your thoughts.

[OldSpot]

@vala

Well I was sent the wrong relay so not been able to set it up yet but a circuit like this would work:

 

Edited September 22, 2021 by OldSpot

[vala]

@RHayes @OldSpot

 

So I've checked on the heat load in kW for the UFH at present (just upstairs) and its coming out at 7kW. Downstairs at present comes out at 8-9kW. Boiler is an oil combi boiler rated at 12-18kW. It was present when we moved into the house and I wasn't made aware of any changes to the boiler so assume its still factory set in the middle at 15kW.

I actually received another email from Thermosense showing the connections on the back of these programmers. Looks like they'd also require power off the S Plan wiring centre. If I was to use these what would A1 and A2 on your diagram refer to? On the programmer I can make out, normally open, closed and normally closed. Connections 10, 11, 12 I can't make out what they are.

They also noted the hysteresis on these is adjustable up to 50º from the set point.

 

@OldSpot

The latching relay you've done a drawing for...are they the type that look like RCBO's for a consumer unit? They're the only ones I can find when searching for them.

[dpmiller]

10-12 are for the sensor.

[vala]

1 hour ago, dpmiller said:

10-12 are for the sensor.

@dpmiller thanks for this.

[RHayes]

@vala

Ok, thanks for the detail of the boiler etc.  So with no demand from the UFH the boiler will make up the 33 litres of water from 40 to 60 degrees in about 4 minutes at 15 kW.  If you were to put the stats at 1/4 adn 3/4 of the tank (assuming the connections suit this) this would increase the volume to circa 50 liters and the time would be about 5 or 6 minutes.

 

Realisticly not all of the underfloor heaitng will be on at the same time so the boiler is likely to be providing more than required for a large proportion of time.  I expect to get a cycle of boiler on for 8 or 9 minutes and then off for 10 or even 12 minutes whilst the underfloor heating uses the buffer generated.

 

The relay in the drawing from OldSpot is a simple DPST (Double Pole Single Throw) relay.  (A double through relay would work just as well).  The can look similar to a RCBO and can be bought as Din Rail moutable.  

 

As mentioned previously the relay will only be needed if you go for 2 stats/sensors and you also won't need the wide histerisis if you go with 2.  Alternatively use one stat and use the wide histerisis of maybe 15 degrees (40 to 70).

[vala]

@RHayes

Thanks for your reply.,

So the way I'm seeing it is I could use the single stat I can get through Newark with no other components. Haven't confirmed with them the hysteresis on these however from info I've read should be around 8-10º.

Option 2 would be to go for the Thermosense sensors and controllers, and set these to 0º hysteresis. How would these wire up? I can make out the power inputs on the back of the units, and from @dpmiller input, 10-12 will be for the sensor.

Option 3 seems to be using 2 stats (I assume the ones provided by Newark will suffice), and connecting these up via a DPST relay. I've searched for a double pole through relay, as you mentioned, but can't find any examples of these. Do you have a link to one? With this set up, unless the stats have adjustable hysteresis so can be set to 0, then surely the stats will each have a 8-10º range of the desired temperature further increasing the range?

[dpmiller]

why not one Thermosense controller and configure a (say) 20c hysteresis?

[vala]

13 minutes ago, dpmiller said:

why not one Thermosense controller and configure a (say) 20c hysteresis?

 

@dpmiller I've not considered that option as I thought it to be a more complicated way to achieve a similar outcome to the single thermostat that could be supplied by Newark Cylinders. On the assumption the stat from there has a hysteresis of 8-10º.

I saw that as an option that involved more components and more wiring for a similar goal, so hadn't entertained the idea.

[RHayes]

@vala

If you have 1 thermostat, whether the Newark one or the Thermosense one the wiring will be simple and straightforward.  If you are going for 2 thermosats, (placed at different heights in the cylinder or at the same height with different set points) then you'll need a relay and follow the wiring diagram from @OldSpot.  DPST relays are less comon than DPDT.  However there is a wide range here https://tinyurl.com/cnt4j5mp

 

https://uk.rs-online.com/web/p/non-latching-relays/1217814 and https://uk.rs-online.com/web/p/relay-sockets/1217825/ together would do it.

Or 

https://uk.rs-online.com/web/p/non-latching-relays/7943715 as a single item with easier and neater install.

On 22/09/2021 at 08:13, OldSpot said:

@vala

Well I was sent the wrong relay so not been able to set it up yet but a circuit like this would work:

 

 

[OldSpot]

There's also a controller made by Elitech - the EK-3010 - which allows you to set ON/OFF temperatures. It uses an NTC 10KΩ temperature probe which is supplied. Less than £20 but looks like you'll also need an enclosure ~ £10

[vala]

@OldSpot have you come across any enclosures for the DPDT relay?

Also I've been in touch with a company called EPH Controls. They do a digital thermostat that has adjustable hysteresis which can be set to 0° so thinking this could be ideal to have 2 fixed set points.

They're a bit dearer though at around £70 each.

[OldSpot]

@vala

Apologies, I missed your question about the relay previously. Yes, it's like an RCBO/RCD/MCB.

There are a few companies who make them. One I've found is called Geya and another Eltako. The relay "clips" on to a standard DIN rail. So if you do a search for din rail enclosure it'll throw a few up.

Hth

 

On reflection, having read through the thoughts of those on this thread (Thank you!), I think I'm going to go with the simpler Elitech set up. This seems to be a simpler solution.

It means:

• there will be less frequent bolier cycles (which are controllable)
• allows the buffer to be configured with a single thermostat
• configurable, generous wide dead band for ON/OFF temps.
• Cheaper, wider range of tank options

[vala]

@OldSpot

Thanks for confirming that.

 

Since speaking with EPH with regards to their digital cylinder stat I too am thinking the same.

Trying to understand whether 2 stats at different locations will mean a worthy amount extra of time between cycling over a single stat measuring from 1 point but with a wider hysteresis. With that EPH thermostat I could set the hysteresis to cover a temp range between 40-65deg (it's adjustable in 0.5° increments.

I guess the next decision would be at what point to fit the single stat?

2/3's up the tank?

[vala]

@RHayes

Today I took the cover off the control panel on the boiler to investigate to where the 5 core cable connected to,

Am I correct in thinking I need a 5 core heat resistant flex, as I'll be connecting live, earth and neutral (as per the image) to my S Plan, and then the black will be in the same connection at the boiler as the image but go to 1 on my S Plan. Then the grey will be in the same connection on the boiler and 10 on my S Plan. And both should be sleeved with brown at both ends.

I will then still have to have a jumper in the same connectors as per the image.

 

[RHayes]

@vala

 

Correct, the black is a permanent live out to 1 on the S plan

Correct, the grey will be from 10 on the S plan

the white link is just for hot water which puzzles me as i thought it was a combi.  The white link would effectivly keep the boiler on permanently.  I haven't come across this before but it may be needed for the combi and could be an option for timed hot water if needed.  Perhaps someone who is more familiar with Comi's can confirm.

[vala]

@RHayes

Thabk you for confirming.

According to the MI the white link is used when there's no timer/programmer for the hot water. So I guess it's on permanently when there's a demand being called for.

 

And I got the thermostat controller sorted. Spoke to a heating engineer who had done more installs like this, especially with oil, and he uses a Grant temperature difference controller. This monitors the temperature via 2 thermostat probes (which is included). Then when there's a call for heat and the buffer needs topping up, via a relay (I can link to this if interested) it fires up the boiler.

 

Buffer arrives tomorrow so hopefully at some point I'll plumb it all in!

 

[RHayes]

Thanks @vala

 

I would be interested in the Grant temperature difference controller as I am due to be doing something similar at my place (when i have some spare time to finally set it up - ha ha).

[OldSpot]

@vala @RHayes

Just coming back to this thread and apologies for the delay as I've been away.

I have successfully managed to wire up a DIN relay in the two stats configuration that we previously discussed.

I have tested the system using two switches and a light bulb. 

The switches representing the two tank stats and the bulb represents the "call for heat" from the boiler.

If you want to see the circuit working pm me and I'll send you a video clip.

The wiring is pretty simple and I'll put a diagram up later if anyone is interested.

 

The relay that I have used is a Heschen ct1-25, they can be found from various online sellers for around £8.50. I'm not promoting this one in particular and there are of course other brands available.

I have also bought a small DIN rail enclosure (~£11) to house it in.

 

Hth.

Edited November 4, 2021 by OldSpot

[vala]

@OldSpot @RHayes

 

This is the controller I went with,

https://grantengineering.ie/media/1299/grant-gsx1-solar-controller-gs222765-manual-doc97-rev00-november-2013.pdf
 

Wired it to the boiler via the S Plan and using one of these to fire up the boiler when needed

https://www.discountfiresupplies.co.uk/product/280/555/Easy-Relay-240V-Mains-Relay-(230V-AC-50_60Hz-Coil)-in-White-or-Red-Single-Gang-Box?utm_source=Google%2BProducts&utm_medium=Price%2BComparison&utm_campaign=Google%2BProducts&gclid=EAIaIQobChMIiJLXssL_8wIVBLDtCh3MKgkqEAQYAiABEgJLlPD_BwE#148

 

Got recommended this set up via another heating engineer whose done more of these setups.

The Grant controller is used in thermostat mode, and comes with 2 probes. This just monitors the temperature of the tank via the 2 probes.

The relay is used to engage the boiler when needed.

Had another things crop up last weekend so hoping if no hiccups I'll get onto firing it all up this weekend so can report back.

 

Edited November 4, 2021 by vala

[vala]

So a number of months have passed and the heating system all worked well during a short testing phase late last year. It's now on full time, as we're hopefully moving back in early Feb. Only issue was the temp probes being in the wrong connections on the Grant controller but a quick swap now has the buffer heated to 75º when there's a call for heat, and this doesn't happen unless the buffer is below 45º. Set this minimum temp in the grant controller as that's, at present, the flow temp at the manifold. More experimenting is needed, but at present with nothing on the first floor (awaiting carpets to be fitted this week) any lower then 45º flow temp and the air temp really struggles to come up to what has been set. It has even got cooler! Have purchased a thermal camera to check for any heat loss so will do more research with that.

One thing I have noticed during these cold days/nights is that the boiler's frost protection kicks in as and when it needs to. As it heats up and circulates water, this does make its way to the buffer vessel and tops up the heat there (even when there's no call for heat from the UFH). Would this be considered a little perk so as not to waste any heat being generated, or is this a negative? Not sure why it would be a negative but I'm open to suggestions.