Heating systems
in the heating system is fundamental to the comfort and wellbeing of the workforce. The correct design and accurate implementation of central heating and chilled water systems (CHW), will provide the right balance for optimum comfort levels and effective temperature control all year round. Heating systems in public spaces such as
office blocks, retail outlets, hotels, hospitals and schools come under much stress, with multiple variants potentially compromising the smooth running of a system. Therefore it is crucial that systems in
commercial buildings must be designed to accommodate the movement of people, the use of electronic appliances, open windows and doors, and potentially individuals tampering with thermostatic controls. As well as causing huge inefficiencies in the heating system, a combination of all of these factors contributes to an environment which can be either too hot or too cold, have drafts, or not enough ventilation. In a work environment, poor temperature
control can have the knock-on effect of poor performance, with overzealous use of heating, as well as icy blasts from CHW units, which are both troublesome and uncomfortable for a workforce. In order to achieve a comfortable
environment and enhance the wellbeing of those within it, the focus for heating engineers should be on balance and control. In engineering terms ‘T set’ is the
desired room temperature that needs to be controlled exactly at all times of year and throughout all times of the day. With poor balance and control, the
system swings become too great, which causes extreme temperatures in the environment resulting in energy wastage. A properly balanced variable volume
system can only be achieved with the correct set of dynamic balancing and control valves. These ensure the correct distribution of flow throughout the whole system irrespective of any pressure changes or the partial system load that will inevitably occur for the vast majority of the building’s operational life. If the system is not balanced properly it
22 June 2017
A balancing act F
or HVAC engineers working in office environments and other public buildings, striking the right balance
will result in unequal distribution of the flow, so there will be a surplus effect in some of the terminals and not enough in others. The result of this will be that the desired heating or cooling will not be delivered in all parts of the installation. One solution is the use of Differential
Pressure Control Valves (DPCVs) which have proved to be extremely efficient in helping to stabilise the temperature in heating systems. The Thermostatic Radiator Valve is another essential tool for heating engineers to help create a comfortable environment with greater efficiency. The TRV with a temperature sensor head is designed to reduce and eventually shut-off flow to the radiator when the temperature reaches set-point. It is apparent that in each circuit when this temperature control happens, with all other conditions remaining the same that differential pressures will increase. With a traditional static balancing valve
approach, this increase in pressure will not be controlled so that more flow will occur in the branch - resulting in wasteful overflow on those radiators. Variable speed pumps will also help by
speed reduction and subsequent differential pressure lowering. This regulation is only local to the pump that must always deliver sufficient performance for the index circuit. The index circuit position changes within variable volume designs to the extent that absolute pump regulation within all sub- circuits is impossible to achieve, and a degree of over pressure is inevitable. Interestingly, modern airtight
commercial buildings with high occupancy,
Albion Valves, technical specifications manager, Paul Wightman considers the aspect of comfort in modern heating systems, and the technical challenges faced by UK heating engineers to maintain a comfortable and healthy climate for people to live and work in
numerous electrical appliances and high lighting levels dictate heating loads which are often small even in the traditional heating season of winter. If a radiator circuit such as above
requires approximately 15-20kPa differential pressure for design duty flow rate then this should be maintained at all duties ranging from design load (<2% frequency) through partial load down to near 0 load (high frequency). Inclusion of DPCVs removes these
pressure fluctuations, so enabling all TRVs within the circuit to maintain good temperature control, as the differential pressure across them is relatively stable irrespective of other circuit’s control valve operations or pump speed changes. This is particularly important for control valves like TRVs that are low flow and self- acting devices as differential pressures of circa 35-40kPa may create potential noise issues within the TRV due to fluid velocity. The maximum DP that a typical TRV can close against is 60kPa. Clearly if this is exceeded then there will be no control and temperature set-points will be exceeded and energy wasted, not to mention the complaints regarding lack of comfort and TRV and pipework noise. The DPCV creates a robust system that not only simplifies commissioning, as each DPCV controlled circuit and can be balanced in isolation, but also allows for future expansion and phased installation without the need for re-commissioning as would be necessary with traditional static balancing. TRVs come with lockable, tamper-proof
temperature settings which make them suitable for commercial environments. In addition, a pre-setting valve position allows individual radiator or emitters to be flow- set at the design stage and so reducing installation time by avoiding the cumbersome and time-consuming lock shield valve commissioning approach. Similarly, in installations that require
Paul Wightman, Albion Valves’ technical specifications manager
balance to be controlled in a specific location, e.g. one point of delivery to a room, Pressure Independent Control Balancing Valves (PICVs) can be used. These are particularly effective on 4-pipe heating and chilled water units e.g. Fan Coil Units (FCUS) that can overheat the space or emit chilly blasts when over-circulating chilled water in the system.
www.heatingandventilating.net
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