Bit of a resurrection of old thread but as autumn starts I’m looking ahead to winter now. 

year 1 we had no issues with the ASHP performance. Last winter we did though and they persisted. It struggled to get back up to temp after frost cycles and comfort temps were struggling to be hit in cold temps. 

The different I think is that in the year between we built a garage with an office above it and that also has a heating and hot water demand. 

I spoke to Grant who said I needed a Volumiser as we have no LLH. Turns Out we do of course have a volumiser vessel (18ltr) but they mean the 30 ltr external volumiser with back up immersion to get more volume into the system at to help it with defrost cycles during the colder outdoor temps. 

this is now getting retrofitted next week. I expect it should make a difference. Time will tell! 

@marvinator80 that's interesting. I know from your previous install pictures you would be struggling to make space for an internal volumiser. The 3kW immersion in the Grant LLH I've found to be a good help with the defrost days when the unit is continually frosting up and defrosting every 45-60 minutes. It's altered my opinion a little on the LLH, which I was minded to get rid of, but the built in immersion is certainly a benefit. It just helps the defrost recovery, and shoves 3kW more heat energy into the hydronic circuit after the ASHP before the emitters. That's right where I need it when the LWT from the ASHP has dropped a little too low during defrost. Also means the leaving water temperature recovers much quicker and the issue of the house not reaching an adequate internal temperature in the morning is mitigated. I also have the immersion programmed as a nuclear option to kick out 3kW if the outdoor air temperature drops to -5degC until it rises to -3degC. At those temperatures my marginally sized 10kW Aerona unit really does need a helping hand. We might see -5degC on just 2 or 3 days a year where I am, so I ignore the electricity consumption those days!

@allyfish perfect Ally. That’s exactly what I’m going for. Previous year it was fine but with the addition of the garage (I think) it was struggling last year due to frost cycles. We weren’t cold but it wouldn’t have got to 22. More like 19.5-20.5 on cold days which just feels too frugal. We would end up putting the wood burner on all day rather than just in the evening.

Posted by: @allyfish

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altered my opinion a little on the LLH, which I was minded to get rid of, but the built in immersion is certainly a benefit

Instead of LLH just configure as a volumiser in the flow from the ASHP. Have the benefits of increased water volume and benefit you see with the immersion. And none of the downsides of a LLH. And you can get rid of the secondary circuit pump.

@marvinator80

Have you considered installing an A2A heat pump to heat the garage and office? 

Posted by: @derek-m

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@marvinator80

Have you considered installing an A2A heat pump to heat the garage and office? 

I have thought about it. Or a tall radiator maybe behind my desk. There’s currently 3 radiators including a small one in the little shower room. Hot water doesn’t seem to be a problem but I think adding on 3 radiators as well as the 15 metres of underground piping might have impacted the volume. 

As you can see I had to plug in electric heaters up there a couple of days last winter.

Posted by: @johnmo

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Instead of LLH just configure as a volumiser in the flow from the ASHP. Have the benefits of increased water volume and benefit you see with the immersion. And none of the downsides of a LLH. And you can get rid of the secondary circuit pump.

Well ideally @johnmo, but I have a coupe of things that work against that; I have a 22 rad system over 3 floors, 28mm CU primary, 22 and 15mm Cu secondary. At the moment the primary pump in my retrofit Aerona 10kW is on speed setting 2, the secondary pump, a ubiquitous Grundfos UPS 3 15-50, is on speed setting 3. At those settings, the LLH is in balance and I have adequate system flow around 22-24 lpm.

I doubt the primary pump would achieve the required flow on it's own due to hydraulic capacity of the piping system that was installed for a high delta T fired boiler.

If I had the Grant Aerona 13kW installed, as was originally the plan, the pump in that unit has a higher capacity head/flow in all 3 speed settings. I probably could have got away with the in-built primary pump and could do what you suggest. It's something I've previously considered and discounted for the reasons stated - without major pipework modification I would very likely need a secondary pump anyway.

A 10kW unit is a big ask on a 3 floor 22 rad system, and it is marginally sized, perhaps a little undersized, but issues with the DNO and my 80kW main fuse, plus which Grant units were or were not 'connect and notify' at the time of installation, forced my hand. For that reason the 3kW immersion provides a welcome boost during defrost as the 10kW unit takes much longer to recover LWT than a 13kW would. The 3kW shortfall in ASHP capacity is simply substituted by the immersion.

It is what it is now, and with total energy bills for a 4-bed all-electric house at under £1K at year, I'm happy with the comfort, performance and efficiency as-is. 🙂

PS: nice man-cave @marvinator80! 

That’s the volumiser now been retrofitted. Took them 2 hours. 

I hope it’s well insulated since with a 3kW immersion outside that could increase your bills a lot. How will it be controlled for how often it comes on?

@judith 

hi Judith. The house is 8 years old and well insulated. The volumiser is also very well insulated. I doubt I would feel it hot to the touch even with water in it heated to 60 degrees. 

it probably will increase my bills in the coldest months but not by much as it will mean the house reaches comfort temperature faster on those coldest days so there will be more time when the whole heating system is off.  Last year it struggled to just about make comfort temps (because we added more heated square footage) so the pump ran 24/7 for weeks at a time.

it’s set to activate when the temp drops below 5 degrees as that is the point where defrost cycles start to happen. 

Posted by: @marvinator80

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The house is 8 years old and well insulated.

I have been generally following the thread with interest.

Couple of things I am having trouble to reconcile 

House only 8 years old and well insulated as well as requiring a big heat pump, with an additional heat source.

Is the house just very big?