What is Wrong with our Heat Pump Installation?

Ken Bone

Heat pumps are touted as a sustainable solution for home heating, but transitioning from traditional boiler systems can introduce significant challenges. In our case, the switch to a heat pump was far from seamless. Initially thought to be a moderately well-installed system, it turned out our ASHP was only about 60% effective. This discovery unfolded over years of trial and error, coupled with numerous conversation with professionals and with other homeowners on the Renewable Heating Hub Forums, highlighting a significant potential for improvement.

Realising the complexity of the issue, we engaged Ken Bone (@kenbone) from Ultimate Renewables. His thorough inspection revealed that our system was not only inefficient but also costly to operate. This scenario is not uncommon in homes where legacy heating systems may not be fully compatible or optimally configured for new technologies like air source heat pumps.

During a casual chat (see below) Ken discussed the nuances of our existing system’s failures. Key issues included undersized piping that couldn’t handle the required output, leading to inefficient heating, especially noticeable at the far end of our house where radiators struggled to reach the desired temperature. Our system’s Coefficient of Performance (COP) was also underwhelming at 2.7.

Ken proposed several adjustments to enhance the system’s performance – we’ll be scheduling the work in, in due course. These included resizing and reallocating flow to balance the distribution between the underfloor heating and radiators. He also suggested revisiting the system’s buffer tank configuration to reduce heat loss and increase overall efficiency. His goal was to raise our COP from 2.7 to between 3.5 and 4.

The remediation involved not just technical adjustments but also a reevaluation of the control systems governing the heat pump and distribution network. Ken aimed to create a more ‘open loop’ system to decrease reliance on unnecessary pumps and valves that added complexity and cost. These changes promised not only to improve energy efficiency but also to enhance the comfort levels across different zones of our house.

This experience highlights a broader issue in renewable energy adoption: the necessity of proper design and installation. It underscores the importance of professional expertise, particularly when retrofitting modern systems like ASHPs into existing homes not originally designed for them.

Transitioning to renewable heating systems involves more than just replacing equipment; it requires a deep understanding of both the new technology and the existing home infrastructure. Our story is a poignant reminder of the value of getting the details right the first time around. For homeowners considering similar transitions, thorough professional assessments and interventions can significantly rectify initial inefficiencies, leading to better performance and greater satisfaction.

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Graham
Graham
1 month ago

I have the same problem,i am happy with heatpump. But the pipes in my house are 8mm upstairs with 10mm downstairs.
The engineer told me the 8mm would have to be changed, but the 10mm was ok.
No one told the installer, until i mentioned it to them.
After the work was completed, in 2 days.
No one came to check their work.
I had the system checked during a yearly service, and the engineer was appalled at the quality of the job.
The header tank which i top up when needed,is supported by a woven strap,screwed onto the joist behind it. If the strap fails my house would be flooded.from the loft down.
But as normal these companies are now gone.
My independent engineer is going to address the problems, with 22mm pipe runs instead of 10mm to get the heated water to rads quicker.
My house is cold because of the lower running temp.
I would have also liked an extra immersion heater that was separated from the heat pump. So i could independently control the hot water. Without running a 10kw heat pump in the summer.

Toodles
5622 kWhs
Reply to  Graham
1 month ago

Having to run the heat pump during the summer for DHW should not be a financial penalty; the heat pump should still have a respectable COP and better than using the grid to feed an immersion heater – unless you intend to use solar PV via a diverter to heat the water, your pump would still be the better plan. Regards, Toodles.

Andrew Scott
10 kWhs
1 month ago

I agree entirely that the design of heat pump installations is critical, and of the few plumbers I enquired with and even the technical support from the heat pump supplier did not inspire me with confidence. As a mechanical engineer, I had read and understood all the information and found a heating engineer who was MCS accredited and someone I could discuss the design with and we could work together. Our system has now been in reliable operation for over 7 years, and I am generally pleased with the performance. However, it is not without some issues that if they could be resolved would improve it’s efficiency. Bearing in mind that this is despite us designing and building our own house to include a heat pump and underfloor heating It was probably a couple of years of observation and fiddling before I could see where it could be improved. The system design was 100% compliant with the Heat Pump supplier’s schematics and also the underfloor system design. The main issue I have is short cycling which is caused by two inadequacies. The first is of my own making. Due to the design of the house being quite small, the location of the buffer tank is compromised being above the heat pump rather than beside it and the resulting plumbing design means that very little flow goes via the buffer tank. The second problem is the main issue, and that is that the proprietary control system for the UFH is very basic. Currently when a thermostat calls for heat, the control system starts the UFH circulation pump and opens the respective circuit valve. It also sends a start signal to the heat pump. The heat pump is controlled by both this remote start signal and internally by the return flow temperature settings. If the flow settings are below its lower set point, and it receives the remote start signal the heat pump will start. It will then stop when either the remote signal switches off (i.e. room stats no longer calling) or the high set point for the heat pump flow temperature is reached. I have discussed this in length with the heat pump supplier and installer, but neither have been particularly helpful. What is required in my opinion is that when the room stats stop calling, the underfloor valves should close and stop heating the house, but the circulation pump and heat pump should continue to run until the flow temperature upper set point is reached. In this scenario, the flow would bypass through the buffer tank, until the buffer tank temperature is up to the upper set point. The volume of heated water in the buffer tank will then supply the next demand, until the return flow temperature drops to the lower set point. The overall effect is that the heat pump will run less frequently, but a little longer on each occasion. this will reduce the number of ‘starts per hour’ which will increase it’s operational efficiency. What is now required is an improved control system which I have yet to locate, and a fairly simple plumbing modification. My apologies for this rather long winded explanation, but it does demonstrate that despite our best efforts the importance of experienced and competent design, and that the technology suppliers are not without limitations. Hopefully technology has advanced since our installation.

AllyFish
3153 kWhs
28 days ago


unless you intend to use solar PV via a diverter to heat the water, your pump would still be the better plan.

With BESS the ASHP is best. Charge battery for free from solar, then run ASHP in HW mode for an hour = free hot water + COP advantage that direct immersion via solar diverter doesn’t give! 😀

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