Out with the old and in with the HIU

As district heating schemes continue to grow in popularity amongst residential providers, Pete Mills, Commercial Technical Operations Manager at Bosch Commercial and Industrial, explains just how significant a role the Heat Interface Unit (HIU) plays in enhancing efficiency levels and simplifying maintenance.    

From the late 1960s onwards, district heating schemes were at the height of popularity in the UK, particularly in apartment blocks and densely sited housing. However, this type of solution seemed to gradually fall out of fashion, particularly from the mid 1980’s and onwards as Combi boilers became the preference. Over the last decade though, technology has advanced quite considerably and the solutions available for district heating schemes today are now much improved compared to those in use twenty or thirty years ago. Also a contribution to the overall heating scheme can be made from renewable and low carbon technologies such as Heatpumps, Biomass and Combined Heat & Power (CHP).

As a result, district heating schemes are once again being considered for all types of projects and are fast becoming the heating solution of choice for local authorities and housing associations looking for better ways to make energy savings, reduce the CO2 footprint of their housing stock and help lower fuel bills for tenants in a bid to tackle fuel poverty.

Wide application
From new build social housing projects to large scale refurbishments of blocks of flats and the development of existing buildings, such as old hospitals, into multiple dwellings, district heating schemes are now suitable for a broad spectrum of properties. It’s perhaps not surprising then that there are currently an estimated 250,000 homes thought to be on existing district heating schemes throughout the UK, with numbers are growing all the time.

The advantages of opting for a district heating scheme are many but ease of installation and the ability to have greater control of these types of systems is a huge driver. According to estimations made by the Government, switching to a district heating arrangement whereby HIUs are typically installed instead of individual boilers, can help deliver energy savings of between 30-40% when compared to more traditional heating arrangements.

What’s attractive about district heating schemes is that, from an installation point of view, no gas network – apart from a gas supply into a central energy centre – needs to be piped into buildings or flats. This alone makes district heating an easier option for conversion, refurbishment and new build projects. Removing the need for a complete gas network within a building also means removing the need for the maintenance of that system and any individual boilers associated with it.

Utilising high-efficiency centralised heating plant to deliver low carbon heating and hot water through a network of pipes to individual spaces, such as apartments, the main interface with the end user in any district heating scheme is typically provided by a HIU.  These units are easier to fit than boilers and installers don’t actually need to have gas training qualifications in order to install them, which makes the whole process more cost and time efficient for everyone involved. After all, there is no flue pipe and no gas connection needed!

Advantages of HIUs
Other advantages of installing a HIU include the fact that minimal maintenance is required on an annual basis and during the lifetime of the heating system. For example, if boilers were installed in individual dwellings there would always be the maintenance of those boilers to think about year on year. This would be far more complicated than any maintenance required by a HIU and would also require the engineer to gain access to each and every dwelling to carry out the work.

In a typical block of say 200 flats this presents a huge undertaking, so removing the need for annual servicing makes perfect sense. From an installation viewpoint, there is also less disruption for tenants as it is quicker and easier to fit a distribution unit than a boiler. Another important consideration for housing associations.

Whilst on the subject of ease of installation, as each individual HIU connects into a district heating network supplied from a central plant room, an additional plus-point is they do not require the installation of flue or ventilation routes within properties either. This means they are simple to integrate into a new or existing building without resulting in an unsightly building with lots of flue pipes protruding out of the side of it. Also the sitting of the HIU is simpler as we are not governed by the flue permutations and maximum flue lengths of an individual boiler.

Where lots of flues have been installed in blocks of flats other problems can arise. For example, many older kinds of blocks of flats will probably have internal U-ducts or SE-ducts. These ‘ducts’ are essentially ventilation systems where every single flue installed within a building is discharged into a central shaft to be transported to roof level and expelled into the atmosphere. Whilst this type of arrangement might have worked well with older boilers, these types of system often can’t be converted to cope with modern condensing boilers. Taking a district heating scheme approach therefore helps alleviate these types of issues as well.

In Control 
Perhaps most importantly, from a metering point of view, HIUs allow residents to have better control of the energy they use. Where older schemes were concerned, many tenants will have been used to paying a flat rate for their heat. The problem with this is there is no incentive at all for people to start saving energy.

Lack of control can lead to overproduction of heat and people opening their windows when their flat becomes uncomfortably warm in order to dump heat. In this day and age, this is not an option. Through the installation of HIUs, residents’ energy usage can be better monitored and controlled, which in turn can also help alleviate fuel poverty through more accurate charges being made. Maximum temperatures for domestic hot water and space heating can be set at the commissioning stage, while automatic control of the return temperature in the primary circuit improves system efficiency and saves energy.

As district heating solutions continue to evolve, it is now possible to use lower temperatures for heat networks, which makes the introduction of renewable technologies more feasible.  Looking ahead to the future, where densely populated areas are served by district heating schemes, the idea of being able to connect networks together is another attractive proposition. Connecting networks could mean much better use is made of waste heat sources in the future, helping bring energy usage and fuel costs down even further.

The fact these types of systems can operate independently of fuel sources, or are very straight forward to swap from one fuel type to another also means housing associations and local authorities can expect better stability when it comes to pricing. If the cost of one type of fuel starts to increase, then it would be fairly straight forward to swap over to an alternative source, helping alleviate rising fuel costs for all.

Given the possibilities, it’s not surprising then that the practice of district heating is once again on the increase and fast becoming a mainstream solution for flats and other multi-residential accommodation.

Bosch launches new and improved HIU

Bosch Commercial and Industrial has recently launched an enhanced version of its heat interface unit (HIU) to provide domestic hot water and space heating to properties that are serviced from district heating or centralised boiler plants.

The new HIU features a series of improved benefits such as an ErP compliant modulating space heating pump, and internal system filters on district, central heating and hot water circuits. The easy-to-install unit can be supplied with or without a heat meter and is compatible with the entire Bosch Commercial and Industrial product range.

The new update means the manufacturer can supply four HIU models with flow rates ranging from 14 litres/min to 21 litres/min. Additional accessories can be included with each model, with the highest output model available with summer by-pass, a Differential Pressure Control Valve (DPCV) and a premium glass outer case as standard. The hot water and heating temperature can also be fixed during the commissioning process.

A keyless filling link is also fitted as standard on all new HIU models and is connected from the district/primary side to the heating side so that treated water enters the system. What’s more, the HIU is fully insulated with EPP insulation on the front and rear of the appliance, significantly reducing heat loss and minimising system noise compared with non-insulated HIUs.


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