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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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heat pump

Mars

(@editor)

Illustrious Member Admin

Joined: 6 years ago

Posts: 4809

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.

New to heat pumps? Take the Heat Pump Fundamentals course and use INTRO50 at checkout for 50% off.
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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: 6 years ago

Posts: 4809

02/03/2024 10:49 pm

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

New to heat pumps? Take the Heat Pump Fundamentals course and use INTRO50 at checkout for 50% off.
Rewritten and updated for 2027
📘 From Zero to Heat Pump Hero
🛠️ Bodge Buster

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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?