Willis heater not heating! Scaled up?

[TerryE]

Air tightness and MVHR?  Thermal bridges?  You have the sums using a basic heat balance spreadsheet as per Jeremy's linked above. What is the average outside temp for your winter quarter?  Ditto daily heat loss?  Plug in the numbers and per kWh electricity costs.  Can you live with this run rate?

 

Edited February 24, 2021 by TerryE

[Nickfromwales]

14 hours 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?

 

https://www.ebay.co.uk/itm/NEW-HOME-AIR-SOURCE-AIR-TO-WATER-HEAT-PUMP-HEATER-8KW-RRP-1499/353377298391?hash=item5246eda7d7%3Ag%3AJF8AAMXQU6tQ9u81&LH_BIN=1

 

Change of £1100. I'd recommend against heating anything other than an uber-performing dwelling with direct electricity, as it'll get expensive very quickly!

On 23/02/2021 at 14:37, TerryE said:

I only have one Willis heating a 3 storey passive house.

Yup, they are pretty impressive for the size and cost!

 

On 23/02/2021 at 19:48, bobh said:

a coup!e of Willis will cope

I always fit 2x on my clients M&E projects as a) they're cheaper than shoplifting,  and b) if one fails you still have some degree of heating whilst you order the replacement. If you're not 'hands on' then it's best to fit 2x so you can wait for a plumber without suffering any real inconvenience.   

[TerryE]

1 hour ago, Nickfromwales said:

I always fit 2x on my clients M&E projects as a) they're cheaper than shoplifting,  and b) if one fails you still have some degree of heating whilst you order the replacement. If you're not 'hands on' then it's best to fit 2x so you can wait for a plumber without suffering any real inconvenience.   

 

I agree that fitting two is good idea, but if you have a properly insulated slab then it will quickly get far too hot if pump 6kW into it.

[bobh]

3 hours ago, TerryE said:

Air tightness and MVHR?  Thermal bridges?  You have the sums using a basic heat balance spreadsheet as per Jeremy's linked above. What is the average outside temp for your winter quarter?  Ditto daily heat loss?  Plug in the numbers and per kWh electricity costs.  Can you live with this run rate?

 

Air tightness presumably will come from our attention to detail during the build, it's sips panels and we will be looking to achieve a good standard.

Thermal bridges have hopefully been designed to a minimum, we are having to go with the architects experience on this but I can't see any obvious issues in the design

 

 

2 hours ago, Nickfromwales said:

https://www.ebay.co.uk/itm/NEW-HOME-AIR-SOURCE-AIR-TO-WATER-HEAT-PUMP-HEATER-8KW-RRP-1499/353377298391?hash=item5246eda7d7%3Ag%3AJF8AAMXQU6tQ9u81&LH_BIN=1

 

Change of £1100. I'd recommend against heating anything other than an uber-performing dwelling with direct electricity, as it'll get expensive very quickly!

Yup, they are pretty impressive for the size and cost!

 

I always fit 2x on my clients M&E projects as a) they're cheaper than shoplifting,  and b) if one fails you still have some degree of heating whilst you order the replacement. If you're not 'hands on' then it's best to fit 2x so you can wait for a plumber without suffering any real inconvenience.   

That's a very cheap ashp and changes the possibilities, that said is it too cheap? Has anyone actually fitted a had good results from one of these units?

Fitting 2 Willis in a system would seem the best option especially as they are so cheap, if we end up using them I would probably consider have a spare on the shelf in case of failures as getting spares delivered to a Scottish island can sometimes take a while. We are very hands on and will be doing the great part of the build ourselves.

[Nickfromwales]

A few have fitted ‘cheap’ ASHP’s ( @readiescards bought a 9kW IVT for £700 iirc and it’s still going and in a rental / @PeterW same circa £900? All still performing admirably.  ). 
Is a Willis heater “too cheap”? 
Work it on a lifespan of say a decade, do the maths, and make your choice on that. Any new half decent HP should see a decade out with ease. 

[Nickfromwales]

2 hours ago, TerryE said:

 

I agree that fitting two is good idea, but if you have a properly insulated slab then it will quickly get far too hot if pump 6kW into it.

I turn the stats down to circa 35-45oC depending upon the type of dwelling / emitter. It won’t pump 6kW in unless 6kW is required, the stats will simply allow the arrangement to crudely ‘modulate’. As I install these systems for Joe Public, I have to show diligence so I always aim at around 50-100% redundancy where it’s not cost prohibitive. The heating controls do of course need to be robust fir one, and I say that with the fact that I always fit low temp suited UFH setups to manage / regulate heat input to the dwelling ( ergo overheating has not ever been an issue ). You can drive a Ferrari to the shops at 10 mph   
I would agree with an ethos of fitting one, and buying a spare to sit on the shelf ready to go, but if Mrs Public loses the heating whilst the hubby / household plumber is unavailable, the double setup will be appreciated and understood   

[Nickfromwales]

Appreciated by some, anyhow ?

[bobh]

Thanks so much for everyone's advise. I'm going to look long and hard again at ashp

[Jilly]

18 hours ago, bobh said:

Air tightness presumably will come from our attention to detail during the build, it's sips panels and we will be looking to achieve a good standard.

Thermal bridges have hopefully been designed to a minimum, we are having to go with the architects experience on this but I can't see any obvious issues in the design

 

 

That's a very cheap ashp and changes the possibilities, that said is it too cheap? Has anyone actually fitted a had good results from one of these units?

Fitting 2 Willis in a system would seem the best option especially as they are so cheap, if we end up using them I would probably consider have a spare on the shelf in case of failures as getting spares delivered to a Scottish island can sometimes take a while. We are very hands on and will be doing the great part of the build ourselves.

Gulp, I could afford one for that price, I'm just a bit scared to do it and to work out how to fit it...

[oranjeboom]

On 23/02/2021 at 07:07, bobh said:

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

 

Sorry for the delay! It coped okay, though during colder spells we did need it on running a bit longer. The 2nd pump did the trick and no more issues with scaling (soft water throughout helped also). House is not passive and I still need to get the EWI done hopefully this summer. So will leave the setup as is for next winter and see how it performs with better insulation values. I've just finished the loft insulation so now have 500-600mm of insulation up there also.

 

I don't have any automation like Terry has, so it's a very manual process and I try and look at the forecasted temps to know how soon/long I need to have the system on for. But for now it will do.