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Temporary heat source for UFH: Willis heaters


oranjeboom

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After various delays, the time has come to get some heat into the house, and as there have been a few on BH that have gone down the route of Willis, thought I would give it a go as well. Hopefully others will find the blog entry also.

 

Background:

  • Renovated (3G passiv-rated windows, 120mm EPS EWI, 400mm loft insul, MVHR - not tested air leakiness yet) / extended (175mm SIPs) south facing detached house, East Kent
  • 156sqm of wet UFH in 100mm concrete (with circa 300-375mm EPS insulation)
  • 130L in UFH
  • Wunda 12 port manifold (The heating valve on the manifold operates in the range of 30-70oC)
  • Wunda wired room thermostats for each room (but probably won't use for this temporary setup now)
  • 12Kw eDual for DHW (not to be included as part of Willis setup)
  • 12Kw Sunamp for DHW/UFH (not to be included as part of Willis setup)
  • 3.8Kw PV (potentially have further DIY grid implemented later on)

 

Not looking to cater for worst case low temps as at these times will just plug in some extra heaters:

 

image.thumb.png.295847607acdac4392e32785661847d1.png

 

 

image.thumb.png.c4678aa7fe5231b1bb4fc06732888055.png

 

I originally ordered 2x 12Kw heat batteries for DHW and UFH. Total reliance on the PV in summer and then off-peak grid in the winter. An all electric approach initially without ASHP. Not keen to spend £8-10k on an MCS installed heat pump to get back an estimated / possible £8-10k. Installers seem very vague on the RHI returns and if I have read correctly, I will have to be metered in order to qualify in any case (as have not lived in the property previously). Since the house will be far above buildreg stds (but below PH level), I simply won't be using the amount of expected input that the installers calculate - hence I won't be getting back the cost of the ASHP supply and fit install. So most likely won't go down the MCS route, and if I were to install an ASHP, it would be a cheapy from fleabay.

 

Having excluded using an ASHP, I learnt that Sunamp were testing various units late 2019. But typically with Sunamp, after continued confusion on their part as to what ASHPs they may have tested/not tested/will be testing soon, I've made the decision that I can't want any longer on their input. So for now I will leave the ASHP option until later on and perhaps consider a propane unit (e.g. Vaillant ) when they come online on a non-RHI basis if I can get a decent install cost.

 

 

 

Willis Heater approach

So therefore looking to heat the UFH with 2x 3Kw willis heaters in order to progress with the internal house work. Thought I'd add some info on here as a lot of people like myself aren't familiar what they are. They originated out of Ireland and still much in use over there. They're essentially external immersion coils and instead of sitting inside a tank are simple external electric units - AKA "Willis jacket", "standard sleeved immersion heater"," inline electric heater". Googling should get you something like this:

Willis Immersion Heater | Shell & 3kW Element

 

Item Weight 1.15 Kg
Product Dimensions

30 x 9 x 9 cm

 

I have tried to get plumbers interested in rigging this up, but they're either not interested or have told me it's not possible/don;t know what a willis heater is. I've managed to plumb in all the Hep2o in the house, so hopefully this won't be too much of a bodge.

 

@TerryE has kindly discussed his set up which is pretty impressive with his DS18B20s set into the walls etc. I'm no programmer and my javscript is mainly simple web stuff and wanting to get heat into the place ASAP, I just want a KISS approach for now. Perhaps later I will think about having some of it programmed using Terry's Node Red option which makes for interesting possibilities. Get a feel for Terry's approach here: 

 

But as I've said, I'm after a bog standard dummies approach to this - seriously KISS:

 

So rather than wiring up room thermostats to the wiring centre, I will for now simply use the Willis inbuilt thermostat and set that to gradual increasing temps from 10oC up to a max of 25oC. A gradual heat increase seems safer in my mind. My only concern is if the Willis thermostat fails and carries on beyond 25oC - up to max temp. Obviously I will have the manifold mixing/blending valve that should restrict temp flow into the UFH also, but is there a further failsafe to consider?

 

Dummies layout.

Eventual Sunamp units (for DHW) will be located on left of manifold so having to locate Willis heaters to right  and expansion vessel top right:

 

1909803810_willissetup2.JPG.ac25b07edcc1b69892d4d33a3c4e984b.JPG

FYI: The immersions need to be turned the other way (so colder water enters the side)

 

Parts list:

  • 15mm copper pipe. The Willis heaters are 15mm so I presume plumbing them into the manifold with 15mm would be okay?
  • 15mm plastic pipe for cold return should suffice I presume?
  • Bottle vents - automatically release any trapped air (like this one). Do I need any and if so where do I place them?
  • Willis heater (ebay has the cheapest)
  • Expansion vessel - 8litres sufficient for total UFH volume of 130L? (like this one
  • 20A DP switch outlet (for each willis) from a 16A MCB (like this one)  . Probably one for each willis
  • Immersion timer (like this one) to be added possibly when I change over to E7 low tarriff rates

 

Will get an electrician to wire it all in for me!

 

Be grateful for comments, suggestions and any answers to above questions!

 

 

FYI: I'm no way the first person to install a Willis, so here's a list of other users on BH that have gone the Willis way and will know more than I do:

 

@dpmiller: photo / details here

@TerryE

@vivienz

@CC45

@chrisb here

@Gav_P - here (Any pics?)

 

Willis instructions:

 

schematic

 

20200117_104153.thumb.jpg.1021a23b20f869bf8516fe2b44605ab9.jpg

 

 

 

 

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159 Comments


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Thanks for the info @Jeremy Harris, @Onoff

 

To limit the number of cable runs from the CU, I also have 2 Sunamp (UniQ eDual 12) units that will need connecting. Could I oversize the radial from CU and have one DP isolator switch covering both sunamp units?

 

Just seeing what's best  in terms of limiting the cabing that has to go in.

 

         4x 7metre runs of 6mm cable for the willis heaters and the sunamps 

 

or:

 

        2x 7metre runs of 10mm cable for the willis heaters and the sunamps 

 

All clipped to cable and only 300mm exposure to loft roll.

 

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If I have understood correctly, then you're having 2 off ~3 kW Willis heaters, plus 2 off ~3 kW Sunamp heating elements.  You could either run 4 off 2.5mm² radials (two for the Sunamps, and two for the Willis heaters) or two off 6mm² radials (one feeding two Willis heaters, the other feeding two Sunamps).

 

The first option means using 4 ways in the CU, but does give the advantage of having each on a dedicated circuit, the second means using 2 ways in the CU.  If you have room in the CU I'd be inclined to run 4 separate radials if it were me.

 

Either is fine in terms of cable size when covered with insulation, voltage drop, etc, as in this table from the blue book, method 101, especially as only a very short length of cable will be under thick insulation anyway:

 

image.png.f463a57bf329007a1fd47e380e8d00c3.png

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Your issue here becomes the switching at the CU and the removal of redundancy in your heating and sunamps as if one unit fails you’re effectively tripping both of your heat sources. 
 

Other option would be a 60A RCD in the CU and then run 16A armoured / XLPE to the room with the sunamps and Willis and have a submain board with 4 MCBs protecting the local installation.  

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4 hours ago, PeterW said:

Your issue here becomes the switching at the CU and the removal of redundancy in your heating and sunamps as if one unit fails you’re effectively tripping both of your heat sources. 
 

Other option would be a 60A RCD in the CU and then run 16A armoured / XLPE to the room with the sunamps and Willis and have a submain board with 4 MCBs protecting the local installation.  

 

Do you mean a 63A RCD? That wouldn't provide over current protection for the armoured run...

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21 hours ago, Jeremy Harris said:

If I have understood correctly, then you're having 2 off ~3 kW Willis heaters, plus 2 off ~3 kW Sunamp heating elements

 

That's correct. I'll run 4 off 2.5mm² radials. May need to add some extra timber in attic to do this, but would leave it elevated above insulation layer that way also.

 

I'll just keep it simple then, rather than having an armoured cable with local submain board

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Just coming back to this now that I want to complete all the wiring to/from consumer unit.

 

Just to be sure, this is what I was going to do in terms of getting 2.5mm² radials for the two Sunamp units:

TyfPH8zQaFMglbAzSvGylEyluT2KK4lK4ARe7bCm9u5zANwMeudqVY61PGkVoliBQGEjA7uDG5c4_q0Rl0SfWKyHVrooaO9gCqUUKXovh2HboCn8uDZ_Vm3-edS0C8di_03Jv9WduNAGIQUZtw1Hxd-nIXzfgry7m16_zCMPI4cjFQnrfcHhWF0auE4OQpHrhEU5SoDHXVYzD7stPgM83a4EhW2gb6J2FS81Irjlt3uAGFmlgY2eKlu7QNf2jNJsrk8MmmTOZfCJHWv_5YHmSMkqtcD3PQh0V8soMLNSwXtqocn8pufmd073WdLnLpYsufp-619bh1EUraT4zVExDxPwtv96RGrVWatRq_89k2H0K-4kypMChn_FHLwk_OXxL5PNC9xD_0dZRoTikLc9TcrjUHATiDZdoHoFYDu8j5XMzqMwWtRxgYnaRxE_AvPoNbmQvPdTp4-JREAV7po1rErP9j1Xuz1qyDLKJrluMYc0ubtGM5hFUMB_6xnBrIa_w2oeQal2h8pWLXcoOztxKUHzN8PXSkr_f9RQMUepSzLbml7WXrCWByxWY4GFW42XKrwrGY1h9LJXGqZi6rgnXOcqek9WluZGh2aKtLcqoi35jOnpX2OVRwR2tIO0N0e54BiTNY8IFc_Pv4sUP0ZG-vXLOjzc1MAhj8bBT5uHrmExpn3QZ64go0jn9Jv3ZYY=w391-h694-no

 

2.5mm² radial from consumer unit to DP switch and then 2.5mm²  to PV diverter? Installer will complete all of the remaining wiring.

 

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