Hi all - we are having our ASHP and UVC installed in a few weeks and would like to make sure we will be making the most of our PV. We have approx 12kW on the roof and will be diverting what we can to the immersion - what's the most efficient/best way to set up the UVC so we are making best use of this energy throughout the year? The installers have told me the UVC will be a Telford Tempest (300l) and will have two immersion elements - the lowest being for the legionella cycle. Can this element also be used for diverted PV power? I'm guessing the diverter would dump the power to the upper most element first, and then switch to the lower element when the top is up to temp. Is that right? Are diverters that sophisticated?

Thanks all

I have a cool energy diverter, this can provide electric to two immersions sequentially, heat top first then bottom.

Ah cool, I was looking at the Eddi diverter - guess it will do the same 

Look in to the details. For example, my economy 7 night rate is basically the same as my PV export rate (15p ISH). I used to run a diverter to heat water, but it doesn't make economic sense. I instead run the heat pump off peak, with a COP of 2, it's twice as cost effective as a heating with solar diverter. And in the summer, from 7am-9am, I could be generating 1kW or more from my PV, making it even cheaper.

 

Also, there's a limit to what you can store, and use. Yes, you could put a massive tank in and heat it to 70c. In the summer that just means additional overheating woes.

 

Finally, I don't see he point in two immersion heaters (just lower) and a legionella cycle is NOT needed.

 

,

Thanks @Conor, but I'm not sure I follow. I thought the diverted allows you to use your excess PV generation but you also get your FIT for the generation - whether younise it or it enters the grid?

29 minutes ago, Tom said:

Thanks @Conor, but I'm not sure I follow. I thought the diverted allows you to use your excess PV generation but you also get your FIT for the generation - whether younise it or it enters the grid?

The FIT has not been available for new installations for something like 10 years now.  But if you do have solar PV on a FIT contract then it is true you get paid for what you generate regardless of who uses it.

 

Any modern PV system can get paid for exporting surplus, but you only get paid for the amount you actually export.

Using a PV diverter gives the ASHP a break to rest it’s weary mechanical bones, stuff breaks.

 

no moving parts in PV diverter set up.

 

8 hours ago, Tom said:

Thanks @Conor, but I'm not sure I follow. I thought the diverted allows you to use your excess PV generation but you also get your FIT for the generation - whether younise it or it enters the grid?

 

I get paid for grid export, no FIT.  

1 hour ago, Conor said:

 

I get paid for grid export, no FIT.  

 

Over here we get 15p per kWh back to grid, on Octopus Tracker I'm paying generally 16-18p per kWh consumed.  Certainly for me right now it's better to pocket the eddi cost and install fee.

Edited March 14, 20242 yr by crispy_wafer

Ah gotcha, we're on a FIT which is about 15 years old I think, so quite good rates and with another 10 years to run IIRC. So for the moment there is no point returning any to the grid if we can use it - economics change when this finishes I guess, as above.

1 hour ago, crispy_wafer said:

we get 15p per kWh back to grid,

 

24 minutes ago, Tom said:

we're on a FIT which is about 15 years old I think, so quite good rates and with another 10 years to run IIRC

I wonder where that money comes from.

Oh yes, the rest of us poor (expletive deleted)ers.

 

15 minutes ago, SteamyTea said:

 

I wonder where that money comes from.

Oh yes, the rest of us poor (expletive deleted)ers.

 

 

Yep! I'll raise a glass to you this evening Steamy

1 minute ago, Tom said:

 

Yep! I'll raise a glass to you this evening Steamy

Cheers, mother (expletive deleted)er

 

12 hours ago, Conor said:

a legionella cycle is NOT needed.

 

Why so?

9 hours ago, TonyT said:

gives the ASHP a break to rest it’s weary mechanical bones, stuff breaks.

Not really sure that is actually true. It's the stopping and starting that breaks machinery, steady running doesn't and never has. It's basically the changes in temperature of the moving of parts, breakdown of boundary lubrication as bearing parts start to lift and be supported by lubricant, that what kills mechanical equipment.

12 minutes ago, Tom said:

Why so?

The general belief to most build hubbers is that with an unvented (sealed system) the chances of getting Legionnaires? is slim to f*ck all. I think most people on here with ASHP and UVC heat to low 40's me included.  the last case in the UK was circa 2000's and IIRC from an air conditioning unit. so on my Samsung I've not connected the immersion to the control so no cycle.

 

46 minutes ago, SteamyTea said:

 

I wonder where that money comes from.

Oh yes, the rest of us poor (expletive deleted)ers.

 

 I assume this is the same for the cheap EV rates ?

15 minutes ago, Tom said:

12 hours ago, Conor said:

a legionella cycle is NOT needed.

 

Why so

Very specific conditions have to be met to actually get infected 

Those conditions just don't happen in the domestic UK DHW systems.

Most houses have chlorinated water supply, don't store much water for very long, and then don't atomise that water to the perfect size to be inhaled by a high risk person.

Unlike old A/C units that used recycled water to cool.

Just the presents of the bacteria in the water supply us not enough to cause a problem.

and using a diverter (no battery in play and only minimal PV) can modulate the excess power in a way that an ASHP can't. No start/stop issues...

4 minutes ago, Jenki said:

The general belief to most build hubbers is that with an unvented (sealed system) the chances of getting Legionnaires? is slim to f*ck all. I think most people on here with ASHP and UVC heat to low 40's me included.  the last case in the UK was circa 2000's and IIRC from an air conditioning unit. so on my Samsung I've not connected the immersion to the control so no cycle.

 

5 minutes ago, SteamyTea said:

Very specific conditions have to be met to actually get infected 

Those conditions just don't happen in the domestic UK DHW systems.

Most houses have chlorinated water supply, don't store much water for very long, and then don't atomise that water to the perfect size to be inhaled by a high risk person.

Unlike old A/C units that used recycled water to cool.

Just the presents of the bacteria in the water supply us not enough to cause a problem.

 

Makes perfect sense, just thought it would be one of those brainless requirements that you are obliged to meet.

11 minutes ago, Tom said:

just thought it would be one of those brainless requirements that you are obliged to meet.

At work we are, not sure what the actual legislation is in the domestic setting.

40 minutes ago, Tom said:

Makes perfect sense, just thought it would be one of those brainless requirements that you are obliged to meet.

Not sure in a domestic setting there is a legal requirement, but get the facts and do a risk assessment. We reheat our cylinder generally twice a day because we use the contents, not because we loose the heat. If you are consuming the cylinder contents daily there is zero risk.  If you go away for a few weeks at a time, you may want to use a sterilisation program to keep you safe. If you have anyone with a weak immune system, avoid the risk use a sterilisation program. Not every case is the same, do the research make your own mind up.

 

Commercial property is different.

We're on a borehole supply which is unfiltered/treated - I wonder what I can culture in the UVC? 

55 minutes ago, Tom said:

We're on a borehole supply which is unfiltered/treated - I wonder what I can culture in the UVC? 

Me also, assume you UV treat and element changed annually, that wil kill anything anyway.

7 hours ago, JohnMo said:

Me also, assume you UV treat and element changed annually, that wil kill anything anyway.

 

No UV for me!  Been fine for the last 3 years, but I wonder if using a UVC in the build changes things. Gas boiler in the caravan up until now

16 minutes ago, Tom said:

No UV for me

No way I would do a borehole without it. Never know what could come out the ground. Not sure I would be comfortable drinking the water without boiling it, without the UV.