Domestic Air Source Heat Pump Project of the year 2020, Sheffield Passivehaus

2020 National Heat Pump Awards

Air Source Heat Pump, Redevelopment Project, Sheffield

Natural Heating


Project Overview provided by Matrix Energy

First of 14 Private Developments with Matrix Energy Systems Ltd and Viessmann systems.

Customer Requirements

The client and Sheffield City Council agreed to develop an old industrial area on the outskirts of Sheffield and aim to achieve the passiv haus standard.

The client, a firm believer in renewable technology had a vision of what they wanted to achieve; to be as carbon neutral as possible. Matrix Energy Systems helped the client realise this vision by working through all of the options available and eventually settled on proposing an air source heat pump to work with mechanical ventilation, solar PV and a battery.

The very nature of the passiv haus standard means that the super insulative properties of all the elements will keep as much energy in the building as possible

The pilot house for this project had to be special and demonstrate the technology working correctly, just like in a show home. This first house would then show interest parties the benefits of the technology mix and its benefits, not only to them financially but also to the environment.

The control of the internal environment was crucial and the selection of the right technology mix to deliver this a major factor in the selection of it. 

The plant equipment had been designed into a small location housing hot water cylinder, buffer vessel and the ventilation fans; it would be a tight squeeze. The PV inverter and the battery were to be fitted in the older section of the garage where a retained brick wall has to integrated into the garage.


The client already had a basic understanding of the benefits of renewable technology but did not understand the many ways in which the technologies could be integrated in order to achieve synergy.

The redevelopment of the area played an important role in the selection of technologies as it is on the edge of the green belt area of Sheffield.

The control of the internal environment meant that system integration was of the upmost importance. Individual components that worked alone and potentially fought against each other would not be an economic solution, but more importantly, they would not be able to maintain the comfort levels necessary.

Ground source heat pump technology was not an option as there was not enough land space for surface collectors, it would have been possible to drill within the property boundary, but the client did not want the disruption.

After discussing available options, it was settled on Viessmann technology as the breadth and range of equipment manufactured by Viessmann would cover all the needs in the property from the heating system, the heat generator, the ventilation and the Solar PV integration. The battery solution settled with was by another German manufacturer called Sonnen.

The client didn’t want to use underfloor heating in the property due to the thermal lag of the system and the heat retention in the thermal mass. Therefore, a radiator system was proposed and designed to run at 35 degrees celcius; this in a normal property would not be effective, but in a property aiming for passiv haus standard, it was more than enough. 

The MVHR system, used rigid metal ducting to distribute pre heated fresh air around the system during winter with a build in bypass for summer months to allow a cooling effect. A Heat exchanger is present in the ventilation so that heating may be applied in the winter months if deemed necessary; this is twofold so that heating can be provided without any increased heat in the radiators or instead of the radiators, again, to quickly control the ambient temperature.

  1. Viessmann Vitotrol 300-B - Remote Control and Diagnostics, Smart PV activation & integration, Ventilation control & integration, Heating control & integration
  2. Viessmann Vitocal 200: 6kW Monobloc ASHP system Integrated Hydraulics with: Hydrobox
  3. Viessmann Vitovent 300-W Type HR A300 Domestic MVHR System
  4. Viessmann Vitocell 100-W: 200L Buffer Vessel
  5. Viessmann Vitocell 100-E: 300L Direct DHW cylinder
  6. Solis Inverter: 3.68kW PV Inverter
  7. Radiator System: GF and FF Designed to work at max 35 degrees celcius
  8. Sonnen Battery: 15kWhours 9.43 AC coupled system

Energy and Environment

Every consideration is given to energy and environment at Matrix as we use an advanced piece of software to model all customers projects, the software is called CYMAP and is a steady state modelling system that allows us to visualise the project in CAD and then apply insulation values to all the fabric elements:

Once we have a complete picture of the peak power demand and the annual energy consumption, then we set to task to deliver this in the most efficient way possible within our customers budget.

Although a large property of 160m2, the aspiration to reach passiv haus standard gives this property less than half the peak heat demand of a comparative building to the existing building regulations. The Peak heat demand of 3.66kW @ -2.2 degree celcius drove the decision to use the 6kW Vitocal 200-A as this was more than enough for the heating and allowed rapid heating of the cylinder with an oversized external heat exchanger.

The ventilation system recovers heat form around the house and uses this to pre heat incoming fresh air, this also takes the demand away from the heat pump and again allows it to operate more efficiently when needed and less frequently during winter months. The addition of a separate heat exchanger into this system allows the heat pump to directly heat the air an become an active heating system rather than just a passive heating system.

The solar PV system can power the entire heating and hot water generation system as well as the ventilation system and all the hydraulic high efficiency pumps. The energy consumption of the system was specified so that it is way below the PV generation capability allowing the system to use PV as much as possible during daylight hours.

A 15kWhour Sonnen battery was installed to enable maximum storage potential of the solar PV system. The nature of the passiv haus design will mean that the heat pump mainly be active for DHW generation rather than heating. This means that even towards winter months the heat pump will mainly only be generating hot water, thus allowing over generation of the PV cells to feed the battery. Any use of the heat pump during sundown will be consumed from energy stored in the battery. The plan in the future is to install an EV charging point which was also the reason for the choice of such a large battery system.

The control of this entire system is managed by the Vitotrol system which can be managed by phone app and is also monitored by remote access by Matrix Energy Systems and Viessmann.

The intelligent switching on of the heat pump will utilise free electricity when available, the control system determines when enough PV generation can run the heat pump and switches it on just like the ‘immersun’ system. The difference here is that the ‘immersun’ put in 3kw and get out 3kw; we put in 1.6kW and get out 6.2kW with an SPF of over 3.75. The battery maximises the ability of the system to do this. The proof of this system operation will allow the next 13 homeowners to make a more informed decision about the refinement and selection of the renewable mix for their homes.


This system links the control of multiple systems for the best effect; linking an ASHP, MVHR, PV, Heating, Battery all controlled from one source.

This system has also been enabled to provide cooling, but now the cooling function is not active as we are leaving the summer heating period. This cooling function can provide some cooling through the installed system, but it is mainly designed to provide cooling into the ventilation system to directly affect the air temperature in the property.

 A single control system was the choice in order to manage all the components in the system and have them working together in harmony.

1. The Viessmann Ventilation system runs all the time providing heat recovery or a bypass for

external fresh air as its basic function. The ventilation system also has a heat exchanger that is linked to the buffer vessel (like a mini radiator in the ductwork) to allow for extra heating of the ventilation air, should this be necessary. During summer months the heat pump will have cooling enabled, the heat exchanger in the ventilation system will also be able to actively cool the air into the property.

2. The Viessmann Air Source Heat Pump is the primary source of heating and cooling into the property. Running very efficiently, the system provides heating to the hot water and heating buffer. The Viessmann system has a unique frost protection system that does not require the use of antifreeze in the system; this means that the lower viscosity in the system and the higher specific heat capacity of the water allow the system to work at maximum efficiency.

3. The buffer vessel allows for an integrated immersion heater. This is a strategic backup only to be used in emergency. It will allow for 3kW of heating which is almost the amount needed by the property in winter conditions. It is also used to provide heat for the ASH defrost function, should there not be enough heat in the system to enable the ASHP to perform this cycle. Therefore, this immersion heater will remain dormant unless a fault condition or failure necessitate its use.

4. The hot water cylinder has an oversized heat exchanger for specific use with heat pumps and this also has an immersion heat for strategic backup of the system. 

5. A 3.96kW Solar PV array was installed using two peak power trackers on a flat roof to maximise the exposure to the sun and maximise generation. The PV array was installed after the March 2019 deadline for the FIT and was not installed just for a tariff benefit. Stuart wanted solar PV to give him some form of energy independence and not be completely reliant on the grid. We pointed out the benefit of generating electricity while consuming it using the heat pump and the decision was easy for Stuart to make.

6. A 15kWhour Sonnen battery was installed in order to maximise the storage of electricity for the property. The full 15kWhour storage is enough to run the entire property on average demand for 2 days including periodic heat pump use. The battery would take just under 4 hours of full sunlight to fully charge if no large demand were present in the house. The Sonnen battery is intelligent and is able to identify components around the property, recognise their consumption data and only allow them to operate if enough storage is available to run them free form grid usage, such as a washing machine, dishwasher or tumble dryer; the heat pump is also set up to run in this way for as long as possible.

7. The Sonnen Battery also has a smart grid function that will allow the end user to export and import energy on a private Sonnen network which will be more cost effective than the national grid, this system is available in Germany now and will be released in the UK in the imminent future.

8. The Viessmann Vitotrol links all the systems together to maintain a comfortable environment and will override the battery to bring on the heat pump if necessary when to use grid electricity.

9. The PV array will only need to operate at 42% output to cover the power requirements o fthe heat pump if no power from the battery is available .

10. If the battery were to solely run the heat pump, it could continuously run the heat pump for just over 9 hours. We have also provided graphical data from our data capture system installed on the project. This project has only just gone live and therefore we have picked a day that at least had a small activation for heat. The data will also be used to determine the benefits of the battery system to the end user and give data with regards to likely storage and generation for future purchase of an electric vehicle. This system uses free electricity where is can and minimises the use of grid electricity. When it does use grid electricity, the heat pump is operating at maximum efficiency in a building designed to achieve passiv haus

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