Heatmiser, Hive and Willis....Help!

[Antonb182]

OK, so i'm adding wet UFH to our outbuilding, slab and pipes are in, manifold is set up and i'm now at the stage of getting it up and running, but I have some questions, which while not insurmountable, I'd definitely benefit from some more sensible/learned opinions on.

 

First one is the Willis. I'm planning on using it to heat two relatively small spaces (approx 25sqm each)  and i'd be super surprised if they ever both needed heating at the same time, so I think i'm going to be OK with a single Willis. However, what i've not figured out, is how people are switching them on/off depending on the system needs. As far as I understand, there's no switched live on the unit, so I assume i'd need a relay/switch of sorts between the (always on) spur and the unit. Is this what people generally do? If not, how are you guys controlling the on off of the Willis?  Not sure if it makes a difference, but the whole thing is going to be controlled via the heatmiser UH4. 

 

Secondly, because I already have them, I was planning on using Hive to control the two rooms in two separate zones. Which in my mind, makes perfect sense, one receiver and one thermostat for each zone. Has anyone else done this already and how did it go? I still have the possibility to switch to something more easily integrated, but i'd definitely rather use something I already have. 

[JohnMo]

To me you don't want Willis on without pump on. So drive a suitably rated multi pin relay from pump switch in wiring centre. Drive and Willis from relay. How you control zones doesn't matter after that. Your flow temperature will be by inbuilt thermostat, but add overheat protection with a pipe stat downstream of Willis interlocked to pump Willis power. So mains to pipe stat, then relay, input. So if pipe too hot Willis is off.

[Antonb182]

I hadn't thought about runaway heat from the Willis, but will definitely consider that too . I had in mind to use something like a Salus 16a relay (Here) (or a more robust Drayton heat switch) and run the call for heat from the wiring centre directly into it, which I guess should then control the on off in line with the rest of the vales/pumps being activated. 

 

If anyone has this setup already in place, I'd be super interested to actually see a pic of how you're already running. 

Edited 6 hours ago by Antonb182

[Nickfromwales]

13 minutes ago, Antonb182 said:

I hadn't thought about runaway heat from the Willis, but will definitely consider that too . I had in mind to use something like a Salus 16a relay (Here) and run the call for heat from the wiring centre directly into it, which I guess should then control the on off in line with the rest of the vales/pumps being activated. 

 

If anyone has this setup already in place, I'd be super interested to actually see a pic of how you're already running. 

@TerryE has this and iirc is using SSR’s to power the Willis.

 

Ive installed Willis heaters on a number of jobs, and I chose to create a recirculating loop which I then glean flow and return from (via some close - coupled T pieces) so this acts like a figure of 8.

 

That way the main pump can circulate freely, regardless of demand, which makes the system less erratic and the UFH manifold pump is hydraulically decoupled and can just do its own thing.

[JohnMo]

7 minutes ago, Antonb182 said:

Salus 16a relay

I used something similar on a 2kW heater it has a melt down after about about a month. You need a relay rated more like 20A, to put up with the switching loads.

 

Build or buy something like this, this is what Grant Boilers use on heat pumps to switch immersions. Choose this link because it shows the inside of box.

https://ebay.us/m/iXxCKs

 

[JohnMo]

1 minute ago, Nickfromwales said:

@TerryE has this and iirc is using SSR’s to power the Willis.

 

Ive installed Willis heaters on a number of jobs, and I chose to create a recirculating loop which I then glean flow and return from (via some close - coupled T pieces) so this acts like a figure of 8.

 

That way the main pump can circulate freely, regardless of demand, which makes the system less erratic and the UFH manifold pump is hydraulically decoupled and can just do its own thing.

Do you use a second pump (on the heater circuit), or does the system rely on buoyant flow across the heating element - similar to the original design for cylinder heating?

[Nickfromwales]

2 hours ago, JohnMo said:

Do you use a second pump (on the heater circuit), or does the system rely on buoyant flow across the heating element - similar to the original design for cylinder heating?

Second (primary) pump.

 

Willis heaters do hot water by convection, when in a hot water cylinder, but for a heating arrangement where there are variables I employ the primary pump. This is to ensure flow across the heater is sufficient to avoid early kettling or any kettling at all.