Here is my heat pump installation with questionable COP in Italy

Air Source Heat Pumps (ASHPs)

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materox345

(@materox345)

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Topic starter 19/11/2025 11:47 am

Hi everybody, this is my first post here, I've been watching the podcasts for a while and I hope it's ok to write here even if I'm not in the UK but in Italy, hills around Florence to be precise.

So I had my heat pump installed 4 years ago and my installation was a disaster. My installer was very very new to heatpumps and had no idea how they worked or how to configure it properly. Due to the lack of expertise, I turned to the internet and with a lot of struggles I've been using somewhat succefully for the past 2 years but, as you know, I'm alwasy monitoring and ttrying to see if I can Improve efficency. A little summary of my setup. I have a viessman 100-s 8kwh (more on that later), connected to a 40L buffer, from the buffer I have 2 wilo para pumps (regulated to low speed), one goes to the radiator circuit and the other to a fancoil circuit (hydronic split? I'm not sure how they're are called in english).

My house is old, it was built in 1823 and had several upgrade trough the years, it's about 80 square meters but on 3 floors + small attic (less than 10 sqm) with the inside unit of the heatpump (it's a split model), water cylinder 300L. My roof is insulated and all the windows are double glazed but pretty old (18 years). The walls are all stone and brick (mixed) and avergae about 70cm thick , 80cm in some spots. Now I know perfectly that I need to upgrade the windows, unfortunately because of town regulations I could'nt insulate the walls, and I can't install PV on my roof (crazy stupid italian legislation).

I upgraded radiators (apparently not enough) when I renovated 4 years ago and installed the heatpump, and installed the fancoils, 4 total. In the summer I use the fancoils to cool and they work very well, here it gets very very hot in summer. In winter I use both radiators and fancoils to heath the house. The system is setup trough weather compensation, and I have no thermostat but several temp sensor in each room for monitoring.

After years of trial and error and research I understood the logic behind my veissman HP, and I can change almost all parameters. This model unfortunately is oversized for my house, it's a nominal 8kw but it's more like a 12kw, meaning that the minimum heat it can generate it's around 4kwh. regarding the logic, basically the whole heating cycle is based on the buffer temperature. The heatpump heats the water to bring it to the target (set by weather comp) and it can increase that temperature based on a tolerance that I can change, after many tests I set it to 4 degrees up or down. This way I drastically reduced the on/off as you can see from the graphs, unfortunatly this setup I think it's not great for efficency (no buffer would be better) but I can't do it differently because of the dual circuit. So In a situation like the graphs attached, the heatpump is constantly running at it's minimum which is 25hz or 28% capacity, and it can run for hours.

The delta T in this cased is calculated by the heat pump that regulates it's secondary pump to the buffer to mantain 5K spread constantly. The problem I have is that the COP is pretty low, as you can see. My data is based on Thermal energy (from heatpump data), electrical energy (shelly em that measures also the 2 pumps on the buffer). I can also see the heat pump's COP as a datapoint and of course that one is higher. Last night it was around 4-6C and the cop was under 3. Am I just unlucky that my model has low efficency? I know that lowering supply temperature will of course increase COP, but I feel there is more to it. Any idea is appreciated . Sorry for my english as it isn't my first language.

I forgot to mention that the target room temperature is achieved and mantained pretty well, but since I live in a moderate climate (maybe it goes below zero a handful of times a year), I was wondering if I can get better COP

This topic was modified 2 hours ago by materox345

This topic was modified 1 hour ago by Mars

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