Domestic hot water timer doing crazy things on my Grant Aerona3 10kW air source heat pump - Domestic Hot Water & Cylinders

RE: Domestic hot water timer doing crazy things on my Grant Aerona3 10kW air source heat pump

Mellow — Mon, 22 Jul 2024 20:50:24 +0000

Thanks @allyfish for the pics and info. Spoke to the installer today and will be returning to replace what is probably a faulty thermostat. I will send details of yours and hopefully they will fit the same.

RE: Domestic hot water timer doing crazy things on my Grant Aerona3 10kW air source heat pump

AllyFish — Mon, 22 Jul 2024 18:38:40 +0000

Hi @mellow, pics of our Grant thermostat below. Rotary control but digital setting. Standard on their pre-plumb cylinders I believe. First one we had was faulty, Grant had to change it out.

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RE: Domestic hot water timer doing crazy things on my Grant Aerona3 10kW air source heat pump

Mellow — Mon, 22 Jul 2024 13:38:34 +0000

Hi @Mellow, I hope I can help, as I have the same Grant 10kW ASHP, Grant branded Heatmiser 4 channel DHW thermostat and a 210L Grant pre-plumbed cylinder.

As you have a similar system @allyfish just wondering what DHW cylinder thermostat you have. From what you have said yours must be a digital one. Ours isn't - Manual cylinder thermostat, Code 542902 - with a dial 25degC to 65degC. I would be interested to know the details of yours if possible please.

Don't know why but I'm thinking that digital is better perhaps.

Thanks.

RE: Domestic hot water timer doing crazy things on my Grant Aerona3 10kW air source heat pump

Derek M — Sat, 20 Jul 2024 18:53:09 +0000

Thanks @derek-m - will research volumiser tomorrow.

[/quote

It is merely a tank through which the return water to the heat pump normally flows, in at the top and out at the bottom. When the heat pump is operating the volume of water within the tank is heated, and therefore acts as a store of thermal energy. When the heat pump performs a defrost cycle some of this thermal energy is used by the heat pump to melt the ice.

RE: Domestic hot water timer doing crazy things on my Grant Aerona3 10kW air source heat pump

Mellow — Sat, 20 Jul 2024 18:45:18 +0000

Thanks @derek-m - will research volumiser tomorrow.

RE: Domestic hot water timer doing crazy things on my Grant Aerona3 10kW air source heat pump

Derek M — Sat, 20 Jul 2024 18:33:01 +0000

@mellow

While it may have a label stating buffer tank, it appears to be piped as a volumiser.

RE: Domestic hot water timer doing crazy things on my Grant Aerona3 10kW air source heat pump

Mellow — Sat, 20 Jul 2024 16:29:27 +0000

@allfyish Reassuring to know a secondary pump may not be needed - can't see one on my system. Have just read the installation manual and it does state that an additional water pump is an optional extra. Think it's related to "water flow rate" and "difference between flow and return water temperatures".

@derek-m There are 2 pipes attached. It does say "Buffer Tank" on the label and 25L - small white tank on wall to the left.

7676

Thanks.

RE: Domestic hot water timer doing crazy things on my Grant Aerona3 10kW air source heat pump

Derek M — Fri, 19 Jul 2024 14:25:01 +0000

@mellow

I doubt that it is a buffer tank if you do not have a secondary water pump, since the system would struggle to work correctly. It may be a volumiser. How many pipe connections are fitted to this tank?

RE: Domestic hot water timer doing crazy things on my Grant Aerona3 10kW air source heat pump

AllyFish — Fri, 19 Jul 2024 13:42:18 +0000

@mellow that will be fine to have the internal pump running on, it will be to remove residual heat and pressure from the condenser inside the ASHP, and thereby the refrigeration circuit. The Grant ASHP controls this pump. It's good to just one internal circulator pump, with no LLH or secondary pump, as that's an efficient set up. Often secondary pumps are fitted where there's little need and the built in circulator can do the job - tends to be a lazy option by installers not familiar or competent at doing basic hydraulic pressure loss calcs to check the capacity of the built-in pump. The buffer vessel is a means of meeting minimum volume in the circuit, usually to aid defrost in winter when the heat source is the water circuit.

RE: Domestic hot water timer doing crazy things on my Grant Aerona3 10kW air source heat pump

Mellow — Fri, 19 Jul 2024 13:04:34 +0000

I was more surprised than anyone that I found a solution. Can't take all the credit though as comments here prompted me to try something different - needing an @derek-m OFF time and @allyfish a heating period every day of the week.

I have looked for a "low loss header" but can't see one. There is a 25L buffer tank. Cannot see a secondary pump either.

Very warm today so the water got to temperature 45degC quickly, about 35 minutes. Tap, fan and compressor symbol turned off but pump symbol stayed on for about 15 minutes. (Black triangle in a circle) symbol. I could hear the pump running and the motorised valve which has an indicator light was open.

I will run again and do some more accurate observations.

Might be useful if I upload pictures of our setup in detail.

Liking the technical explanations of various systems - all above my head but after reading through them something usually sticks.

Thanks one and all.