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Hacking a heat pump to increase heating range over 38C

Air Source Heat Pumps (ASHPs)

Last Post by PercyPenguin 2 years ago

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PercyPenguin

(@percypenguin)

New Member Member

Joined: 2 years ago

Posts: 4

Topic starter 02/03/2024 5:47 pm [#1406]

Hi Everyone,

This is a bit out of the ordinary but I am looking to "hack" my heat pump's controller - let me explain.

I have bought a heat pump to heat my hot tub, it came from liquidated stock so it's unlikely I can return it. I read the instruction manual online before I bought it and it states that the operating range of the water temperature is 9-40 deg C which I took to mean it can heat the water to up to 40 deg C. However, when I received the heat pump there was a sticker on the box saying "Temperature Range Heating 9-35 deg C" which isn't quite hot enough, a hot tub should be 38 deg C or so.

I'm wondering if there's a way to "hack" the controller to make it go the extra 3 degrees. Is there a button combination to put it into a special mode for configuration etc.

I know there's a hundred reasons not to tamper with this stuff but from my perspective there's one really good reason to do it, my wife - she'll kill me if I can get this thing to work!

The heat pump is a Hydro-Pro P8/32.

Any help would be hugely appreciated 🙂

Percy P.

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Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4704

02/03/2024 10:38 pm

Welcome to the forums @percypenguin - this is indeed an odd (but intriguing) question. I’ll put some feelers out and see what the feedback from the pros is.

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PercyPenguin

(@percypenguin)

New Member Member

Joined: 2 years ago

Posts: 4

Topic starter 02/03/2024 10:44 pm

Many thanks @mars I'd really appreciate that. I've been looking at the controller and it's a touch screen device made by Topband and based around a STM32F103 microcontroller if that's of any additional help.

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Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4704

02/03/2024 10:49 pm

@percypenguin have you already installed and tried it to see if it’ll get to 38C?

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HughF

(@hughf)

Honorable Member Member

Joined: 4 years ago

Posts: 489

03/03/2024 7:58 am

Most hot tub heatpump controllers allow you to offset the flow temperature sensor by a fixed value…

failing that you can just fudge the resistance.

disassembling the code and reflashing would be a faff.

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

👍

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PercyPenguin

(@percypenguin)

New Member Member

Joined: 2 years ago

Posts: 4

Topic starter 03/03/2024 4:15 pm

This sounds like it could be a workable solution. I must admit I wasn’t relishing the idea of poking around with code etc.

Is it only possible to fudge the sensor with a resistor if it’s an analogue sensor? I imagine a digital sensor would not play?

I’ll have a look at the settings on the controller to see if there’s an offset setting. I have noticed anything in the manual but then it doesn’t seem to go into great detail.

many thanks 👍

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PercyPenguin

(@percypenguin)

New Member Member

Joined: 2 years ago

Posts: 4

Topic starter 05/03/2024 8:41 pm

@HughF, I've been looking at the heat pump and the manual. I can't see any way of inputting a temperature offset so I've been investigating fudging the sensor.

It looks like the output temperature is monitored by a thermistor near the outlet pipe connection. The thermistor is a 5k ohm by the looks of it but I'm not sure if it's a positive or negative temperature coefficient type so I don't know if I need to increase or decrease the resistance in order to offset the temperature by say +3 degrees C and I also don't know if the thermistor's output is linear.

Do you have any suggestions about what sort of value resistor I should try first? Would it be a good idea to use a variable resistor so that I can trim it or should I just put in a fixed value and set the temperature accordingly?