Willis heater not heating! Scaled up?

[joe90]

1 hour ago, dpmiller said:

bouncing off the control stat any time they want to.

yes but this one is not bouncing off the control stat, it’s tripping out the overheat devise!!!

[dpmiller]

3 minutes ago, joe90 said:

yes but this one is not bouncing off the control stat, it’s tripping out the overheat devise!!!

 

 

Good point, I missed that. Definitely a dodgy stat. Before condemning it completely I'd probably pull it out and pop the cover off to check for welded contacts or (more satisfyingly) whack the terminal box end off something hard and refit/re-try...

[joe90]

12 hours ago, PeterW said:

+1 to that - I would try a decent one like a Backer stat

 

These go down to 15°c and cut out is 65°c so should be fine. 

 

https://www.tlc-direct.co.uk/Products/IHST7slashC.html

for only £7 is it worth arsing around? ?‍♂️

[oranjeboom]

51 minutes ago, joe90 said:

for only £7 is it worth arsing around? ?‍♂️

 

I'll get the Backer one this morning and see if it actually limits the temp but I suspect with limited water, it will also overshoot.

 

Just note that the Tesla 225 in the heater is 11" long.

 

So best replace like for like and get this one even though it's for a 88" immersion?

 

 

[joe90]

Question, why would a thermostat react more slowly than an overheat devise?. Easy test, multimeter across stat terminals, saucepan of water on cooker, slowly raise temp and confirms stat cuts out before overheat devise cuts out!

[dpmiller]

telling ya, welded contacts.

 

Mine- now piped to the TS and both manifolds- was happily pulsing 40-55c yesterday. On test with no flow in the circuit, pumps off, valves closed; no overshoot.

[SteamyTea]

4 hours ago, oranjeboom said:

 

I think it works fine. I may get another one today but I expect it would do the same - ie easily overshoot the target temp in a static low volume water

It almost certainly will. The metals in the element will get hot first, very hot. Then stay hot after power us removed.

With a small volume of water there is just not enough buffering to cope.

[joe90]

But,

 

2 hours ago, dpmiller said:

telling ya, welded contacts.

 

Mine- now piped to the TS and both manifolds- was happily pulsing 40-55c yesterday. On test with no flow in the circuit, pumps off, valves closed; no overshoot.

 

[oranjeboom]

Okay, testing the other Tesla element in 'kettle' type setup as below resulted in the breaker tripping on each attempt (thermostat set to about 30oC).

 

At least the other Tesla one had the safety mechanism kick in. So I replaced both of them with the Backer ones from TLC. And testing one of these new ones, it actually only overshot slightly above 40c in the kettle method.

 

Anyway, the Tesla ones never overheated when I was running the Willis heaters - they just don't cope very well with the kettle method and obvisly not designed to work in such a scenario.

 

Still, I feel the setup with the Backer ones is a bit safer as they operate at a lower temp (if needed) and the safety cut off is also slightly lower than the Tesla ones.

 

NEXT QUESTION: Should I still add inhibitor to the whole system?  I've just flushed it all through (inc loops) with softened water. I do recall reading somewhere that 100% softened water 'may not be best' but can't find the reference now. 

 

[Triassic]

I’m confused, why you would need two circ pumps so close together?

[oranjeboom]

On 06/12/2020 at 18:16, Triassic said:

I’m confused, why you would need two circ pumps so close together?

 

I now have 2 indeed. One pumps the water around the loops (via manifold) and then the other pumps water around the Willis circuit:

 

 

I didn't add any inhibitor to the system, but flushed the whole system (clearing any of the previous inhib) and then re-filled with soft water. Willis heaters don't appear to be hissing any more so hopefully no scale up (since soft water) and the extra pump helps push the water around. Both are set to around 40oC in order to get sufficient temp into the floor. Have it running usually for around 2hrs in the morning and 2hrs later afternoon. Pretty mild temps outside at the moment so will have to wait until the New Year to see whether I need to get an ASHP instead.

[Triassic]

I’ve just got my Willis heater and pump up an running. I used a second hand pump I had in stock, but it keeps tripping the circuit breaker.  Looking online there are loads of circulating pumps ranging from £45 to over £300. Aren’t all circulation pumps not equal ? If not, what should I be looking for in a pump? 

[ProDave]

13 minutes ago, Triassic said:

  Looking online there are loads of circulating pumps ranging from £45 to over £300. Aren’t all circulation pumps not equal ? If not, what should I be looking for in a pump? 

Noise

 

In my experience Wilo are quietest, followed by Grundfoss.  Some of the cheaper ones can be downright noisy.  My UFH manifolds came with cheap ones and I soon swapped them for Wilo

[oranjeboom]

On 16/12/2020 at 17:51, Triassic said:

I’ve just got my Willis heater and pump up an running. I used a second hand pump I had in stock, but it keeps tripping the circuit breaker.  Looking online there are loads of circulating pumps ranging from £45 to over £300. Aren’t all circulation pumps not equal ? If not, what should I be looking for in a pump? 

Is it gunked up at all?

 

I bought this Wilo one. 

 

https://www.toolstation.com/wilo-yonos-pico-circulating-pump/p34661?searchstr=wilo

 

Not sure how that compares against the £10 cheaper one. It's pretty quiet and also has an automatic air bleed thingey.

[bobh]

@oranjeboom how did this system cope with the cold weather we had recently? Did the second pump solve the issue?

Edited February 23, 2021 by bobh

[TerryE]

I am one of the early adopters and advocates of this system.  I only have one Willis heating a 3 storey passive house.  On the 13th at the height of the cold snap where the system predicted a 930 min heating requirement; this was implemented as 420 mins during the E7 window, with the rest split over hourly top-ups once the hall temp had fallen below the boost set-point (22.3°C ).  Three days later, this requirement was down to 460 mins and yesterday it was at 199 mins.  

 

Did the system cope? -- well at one point the hall temperature did drop just below 22.2°C --- Brrrrrhhhh.

 

This isn't going to be the case for every house.  IMO, you really need one with as-built passive class performance, but if you have achieved this then it is fit for purpose. 

Edited February 23, 2021 by TerryE

[bobh]

Thanks @TerryE sound like the system coped admirably

I'm seriously contemplating this system for our new build which isn't up to passive house standards but hopefully as it's only 106m² single storey a coup!e of Willis will cope

[TerryE]

@bobh, the Achilles heel of this approach is that at is core it is using resistive electric heating at say 9p / kWh (off peak) or 15p+ / kWh peak / single tariff to pump those kWh into the environment just like those 1970s storage heaters.  Resistive = a CoP of 1.0 unlike an ASHP which might be 3-4x as efficient or gas which runs at maybe a third to a quarter of the unit price per kWh. The reason it makes sense in my case is that my house is maybe 10× more efficient in terms of heat conservation than a typical build.  Yes, is is very cheap to install, but the run costs can be prohibitive is you don't have an energy-efficient build.  Do the sums before you commit to this path.

[bobh]

@TerryE as usual it comes down to budget, and well in our case location

Quite simply an ashp is beyond our budget and gas isnt available as we are on a Scottish island. How does one predict the energy requirements on a theoretical build innorderto do the sums though?

 

[LA3222]

8 minutes ago, bobh said:

@TerryE as usual it comes down to budget, and well in our case location

Quite simply an ashp is beyond our budget and gas isnt available as we are on a Scottish island. How does one predict the energy requirements on a theoretical build innorderto do the sums though?

 

Use the calculator on this page:

 

Fabric and ventilation heat loss calculator - Heat Insulation - BuildHub.org.uk

 

You need to be very familiar with your build to use it as lots of information is required.

[bobh]

@LA3222 many thanks

[TerryE]

@bobh there is always a trade-off between upfront costs and run-rate ones.  The Willis approach works for us because:

1. My house is perhaps 10× more energy efficient than our previous one, so the total energy input we need to keep the house at a comfortable temperature is small. (e.g. the Willis ran for about 2½ hrs last night at E7 rate).
2. I use an RPi to control how much heat and when I inject it into the slab, and so I can make most use of cheaper tariff rates.  I am about to switch to an Octopus agile tariff to drop these costs further.

However the weakness of this approach is that a Willis works at a CoP of 1, so you have to pay the full electricity unit price for every kWh that you use.

 

If you can't afford an ASHP and you only have ~100m², then have you considered an air-to-air wall mounted unit?  You can get these for around £500 and up for a 12000 BTU (~3 kW) unit that will run at a CoP of around 3.0.  @Jeremy Harris did a topic on the one he installed.  A bit noisy, and one room only but it is a cheap way to pump heat into a house.

Edited February 24, 2021 by TerryE

[bobh]

@TerryE I'd not considered an air to air unit, all I've ever read, heard or experienced of them was quite poor from a whole house point of view. Quite good for an open plan type but not so good at getting heat into various rooms

I'm going to run through the spreadsheet that @LA3222 linked above so I've got something to base calculation on 

Edited February 24, 2021 by bobh

[TerryE]

Something like this: 12000 BTU AC.  

 

IMO, using something like a Willis is part of a package:

• Wall, roof, floor U-values 0.15 or better.  No major thermal bridges.
• Triple glazed windows and doors.
• Airtightness 1.0 ACHP or better
• MVHR with ~90% heat recovery.

If you use a Willis solution, there are two separate Qs

• Will it provide enough heat to do the job?
• Will you be able to afford the monthly bills? 

 

[bobh]

@TerryE we hit most of those specs, just outside on the walls at 0.16 but floor and door are 0.14 and 0.13 respectively.

Triple glazed with average u value of 1.3

I'm just waiting to try and get the local mean temperatures then I can finish the heat loss calculations and hopefully try and answer your 2 questions