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The case for the low loss header
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The case for the low loss header

At the beginning of this year, Grant UK launched its combined volumiser/low loss header for installation with the Aerona³ air source heat pump. In this blog, Neil Sawers, Commercial Technical Manager at Grant UK, explains the design of this unit and provides a case for its place in heat pump installations.

Although I may sound like a broken record, I really don’t think this point can be emphasised enough and that is that installing an air source heat pump is not the same as installing a gas or oil boiler. Over the coming years, the number of heat pump installations is expected to significantly grow and the number of installers entering the market will also increase as the number of fossil fueled appliance installs decline. It is crucial for all heat pump installers that they understand not just how to install, but why they should install a heat pump system in a specific way. Grant, like all manufacturers, need to equip installers with this knowledge and provide products to help achieve this success in the field.

Just as there are many types of system to consider (old or new, underfloor or traditional radiators, micro or mini bore pipe) there are many solutions available to the installer, each one with a different feature or benefit to assist the system operation. Some installers may prefer using a large 250 litre buffer, if they have the space (or a small 30 litre one if they don’t!), some may prefer complete hydraulic separation by using a plate heat exchanger and some that see the benefits of a traditional low-loss header.

This leads me onto Grant’s new combined volumiser/low loss header which was designed after analysing the most common issues our installers were experiencing in the field. There are many factors that can affect the performance of a heat pump – incorrect flow rate, high pressure drop in the pipe work or heat emitters, lack of control to balance the flow rate in each zone, to name but a few. Failure to address one or all of these could affect the performance of the heat pump and could be expensive to remedy after the event. While I am not discounting the benefits of utilising a buffer or plate heat exchanger (although the latter would still need a buffer on the heat pump side to provide the minimum water volume required for the heat pump) I have seen, at first hand, the benefits (not to mention the ease of installation) of using the Grant volumiser/low-loss header.

The Design
The Grant combined volumiser/low loss header is larger than a standard low loss header because it holds 11.5 litres of system volume and accommodates a 3kW back-up heater. The unit, which is manufactured using 3mm mild steel, incorporates 50mm insulation. It is also supplied with a 16A relay, two 28mm isolating valves, a ½” drain cock, a ¼” manual air vent, a reducing bush and four blanking plugs. It has a white, powder coated case, designed to be wall mounted and installed internally and can be piped up to and from either side. The heater can be controlled by the heat pump, the system controls or by a separate air thermostat.

The Function
This unit has multiple functions but principally it serves as a volumiser and hydraulic separator. It provides an extra 11.5 litres to the system volume connected to the heat pump and it also gives hydraulic separation of the primary circuit of the heat pump from the secondary system circuit. This means that the flow rate/differential through the heat pump can be maintained, irrespective of the flow rate/differential required on the system side. The size of the unit also helps to minimise the internal turbulence that can occur when the system mass flow of water exceeds that for the primary heat pump circuit. Furthermore, its factory-fitted 3kW electric immersion element provides a back-up/supplementary heat source if required.

(You can download the electrical and hydraulic schematics for the Aerona³ Installation Packs A, B and C - which incorporate this low loss header and volumiser - in the Grant Heat Pump Installation Manual available to download here.)

The Benefits
The Grant combined volumiser/low loss header enables installers to separate the heat pump from the rest of the system and this is beneficial in many ways. First and foremost, the performance of the heat pump will be protected because the volumiser/low loss header is allowing the heat pump to maintain the target flow temperature while the system side can achieve whatever flow rate/differential is required to deliver the heat to the emitters. Secondly, the header can be used to pair two heat pumps together for larger systems or even a heat pump with an oil or gas boiler. Perfect for even larger systems where the heat pump could only be expected to satisfy a portion of the overall heat loss.

Hopefully I have provided some insight into Grant’s combined volumiser/low loss header, the thinking behind it and an explanation as to why we feel it has a worthy place in a heat pump installation. As I have said already, it is not the only way to install a heat pump and there are experienced engineers who have their own methodologies which work extremely well too. The low loss header is just one way but hopefully it provides engineers with an installer-friendly solution to future-proof their heat pump installations.

You can listen to Neil discussing this topic in further detail in Episode Three of the Net Zero Heating Show and follow the link here to read more about Grant’s heat pump installation kits which include the low loss header.

The case for the low loss header
The Grant Combined Volumiser/Low-Loss Header - Part Code: HPIDSYSLLHKIT
Neil Sawers
Commercial Technical Manager at Grant UK