The demands on environmental systems in commercial buildings will inevitably change to meet the needs of tenants, and to facilitate changes in building use. In recent years, many companies have restructured, resulting in a change in their building’s use and a reorganisation of its internal layout. This inevitably alters the pattern of cooling loads, requiring HVAC systems to be redesigned or adapted to satisfy the new demands. Even where there is no particular change in a building’s use, the environmental systems will often evolve because of technological advancement, or legislative obligation.
This article will consider how these changes may be planned for in the layingout of variable refrigerant volume/variable refrigerant flow (VRV/VRF) systems, as well as looking at how legacy systems may be brought up to current standards.
When a new tenant occupies a building, changes to the existing layout can have a significant impact on the arrangement of the building services. Even with new buildings, the change from a Category A to Category B fit-out (see box overleaf), can result in multiple cellular offices being built within a space that was designed for single open-plan use.
Typically, in ‘Cat A’ designs, fan coils – increasingly commonly served by a distributed VRV/VRF – are placed around the perimeter, with larger (cooling) capacity units towards the middle of the conditioned space. When tenants move in, the design often changes, requiring fan coils to be moved and placed in other areas – for example, local to cellular offices, meeting rooms and other newly created spaces.
When considering VRV/VRF systems, there are decisions that can be made early on in the design process to ensure systems can be altered over short timescales – to reflect the change in building use – with minimal disruption, and without incurring a significantly high initial investment.
As these systems use refrigerant, and sophisticated pressure and flow controllers, proper pipe sizing is key to their operation. As the refrigerant distribution system reaches further into the building, pipe sizes will normally reduce to maintain the correct volumetric flow rates and pressures. Subsequently, moving fan coils to new positions – or adding and removing fan coils – can alter the required pipe sizes, and so necessitate a physical change to the distribution piping.
By careful consideration of future use – and, so, future flow and distribution requirements – such changes can be obviated. For example, since the majority of VRV/VRF systems in temperate regions, such as the UK, are heat recovery systems, the positioning of the distributed control boxes – that dictate whether the attached fan coil(s) are in heating or cooling mode – needs careful consideration. Manufacturers produce distributed control boxes in various single and multi-port configurations, so that they may accommodate a wide variety of potential building layouts. Each individual port can usually support multiple fan coils, so that different fan coils in the same physical ‘control zone’ are maintained in similar operating modes, to ensure that there is no attempt at concurrent heating and cooling – they are not ‘fighting’ each other’s operation.
Typically, multi-port boxes are most suited to places that require a large number of fan coils in a local area, as this can reduce the amount of copper tubing required during installation, whereas single-port boxes are well suited to long runs – such as hotel corridors. However, it is important that the system design is guided by selecting the type that will provide the most-effective and efficient operation – which will normally be that with the shortest overall pipe length to the room fan-coil. Ensuring that the initial system design considers the required flexibility to adapt readily to changing building use – or user – will reduce the disruption when the inevitable change occurs. Manufacturers of VRV/VRF systems have devised solutions to ensure flexibility and longevity of their systems. They consider1 that by properly addressing the challenges of reorganisation – with informed consideration in the preliminary design stage – more than 50% of the cost and time can be saved that would otherwise be expended in a Category B fit-out (as illustrated in Figure 1).
Figure 1: The two distribution boxes have been carefully positioned to satisfy both the category A and B fit-out requirements
For example, it is possible to eliminate the de-gassing of the systems – the vacuum removal of refrigerant gas from the distribution system – when alterations are made. When using multi-port boxes, highquality, non-leak ball valves can be fitted and used to isolate the ports that are not in use. If, for example, in an open-plan Category A office fit-out the space requires five centrally placed fan coils to meet the load, if an eight-way multi-BS box is placed into the space to serve these five fan coils, it will leave three ports available for future alterations. By placing ball valves on these ports, it is then possible that when – for example – cellular offices, extended reception areas or new meeting rooms are built, the contractor only needs to connect the new pipework to the stubs of the available ports. The new pipework requires only to be vacuumed and leak-checked before adding additional refrigerant gas for these sections, using Schrader valves. This approach can save considerable time, money and resources for building services alterations.
Consideration also needs to be paid to the life-cycle of VRV/VRF systems. On average, systems should last around 15 years; indeed, there are some systems, still installed and working, that are more than 20 years old. There are now many options available from manufacturers to enable quick and convenient replacement.
From 1 January 2015, a prohibition2 comes into effect on the use of both new and recycled hydrochlorofluorocarbons HCFCs (including the commonly used R22) in the maintenance and servicing of refrigeration and air conditioning equipment. It is permissible to carry on using equipment that contains HCFCs beyond this date, but it is prohibited to replace any lost HCFC refrigerant. It is estimated that 10,000 to 20,000 VRV systems still operate using R22, which – after the end of this year – will be unserviceable if any intervention in the refrigerant circuit is required. Working with their installers, a major VRV system manufacturer determined that there are still a considerable number of these R22 installed systems in place where the building owner has no particular replacement plan. An indicator of the extent of the work that needs to be undertaken was evidenced within the past three months, when they received an enquiry from a municipal council that had ‘just become aware’ of the ban, and had identified 1,300 sites within its borough that were affected.
To provide a solution for the many systems that are still employing R22 as the working fluid, there are three broad routes for action, as illustrated in an example office installation in Figure 2. These scenarios are not absolute, but provide an indicative comparison of the principal choices available, as explained below. The first option is to ‘do nothing’. As Figure 2 indicates, it may be possible to keep an R22 system running for a while. However, at some point, an intervention into the refrigerant circuit would be required – such as a compressor failure, a leak of some sort, or maybe even something simple, such as a pressure switch requiring replacement. At this point, the system becomes redundant, as R22 cannot be put back into the refrigerant circuit after it has been removed. So a replacement will be required, inevitably causing unplanned downtime of the HVAC system, leading to office disruption and a lack of any heating or cooling. Also, as the older systems are less efficient than modern systems, the operating cost will be more for the same level of air conditioning than for new installations. The graph shows a large increase in cost approximately two years after the ban, providing some indication of the increased capital cost associated with replacing the system – and the additional cost of the disruption to the workplace – that can be avoided by planning the replacement.
The second option is to use ‘drop-in’ replacement refrigerants that are not subject to the same restrictions as R22. Daikin1 has had an R22-based unit on test, running a drop-in refrigerant, for several years, and the company is monitoring the power input, power output (for efficiency), and also the wear and tear on the system (by recording the requirement to replace parts). The system runs, on average, 10% less efficiently with the drop-in refrigerant when compared to its original R22 operation, with a 5% increase in power input and 5% less capacity, depending on conditions. As the dropin refrigerant has different thermodynamic characteristics from that of R22, it has adversely affected the system’s control regime. This has caused excessive wear to the compressor – requiring two replacements in four years – that adds considerably to the cost of system operation. Eventually, this system will also require replacement, shown by the costs for 2018/19, indicated in Figure 2.
Figure 2: Comparison of relative cost for options to meet the impending prohibition of R22 in existing VRV systems
The third option is to plan the replacement as soon as possible. This allows a managed installation, outside of working hours – causing no downtime to the occupants – with the benefit of significantly reduced running costs (potentially 40-50% lower, as shown). This is likely to prove the most cost-effective – and, possibly, the soundest environmental option – for maintaining a system that meets the requirements of the original design.
Manufacturers have developed systems that can replace existing R22 and R407c VRV units, while keeping the original pipework. Manufacturers’ tests have indicated that appropriately installed copper refrigerant pipework has a working life in excess of 30 years. (A recent report produced by the US GSA3 ignored any pipe replacement costs over a 30-year life-cycle analysis, indicating that it concurred with this expectation). Keeping the installed pipework, and replacing the indoor and outdoor units, shortens the installation time – by about 33% – for replacement VRV systems, and enables floor-by-floor, or system-by-system, replacement out of normal business hours to maintain the tenants’ operations without disruption.
Due to the increased operational pressure of R410a equipment – and to conform with the European Pressure Equipment Directive4 – refrigerant pipework sized at 1” 1/8 (28.6mm) that was commonly used for R22 installations needs to have the wall thickness checked to ensure it is suitable for R410a pressures. This may be practically impossible, so some manufacturers produce replacement R410a systems that operate at a reduced pressure, obviating the need for this particular check. The pipework must still be checked for leaks at the operating pressure of the new equipment, but no dye – which is occasionally used for leak detection – should be present in the pipework. (POE oil used as a lubricant in refrigeration systems includes anti-wear and anti-oxidation additives that have an unpredictable performance if mixed with other chemicals, such as dyes). For any retrofit, it is particularly important to check the individual recommendations of manufacturers.
The efficiency of these replacement systems has improved significantly since they were first introduced, contributing to reduced running costs and resultant CO2 emissions, compared with the original systems. This is indicated in Figure 3, which compares the energy efficiency ratio (EER) of 28kW (output) VRV systems based on R22, R407c and R410a, all at the same nominal condition. The EER is a single-point value of the system’s cooling performance – part-load efficiencies of newer systems have significantly improved, compared with older systems, so a comparison of a specific application’s seasonal energy efficiency ratio (SEER) is likely to show even larger relative improvements between new and old systems.
Figure 3: Comparative cooling performance for a 28 kW output VRV unit operating with different refrigerants
A case study of replacement VRV in Japan – of 24 R407c systems, including 126 indoor units – reduced the client-measured system running costs by 44.6%, indicating that there is great opportunity for reducing the ongoing operating costs of VRV/F systems.
There is no standard definition of how the
‘shell and core’ of a commercial building
is finished (known as categories of ‘fitout’).
However, in broad terms:
Category A sets the building so that it
provides a basic level of services ready for
customisation by the tenants. It is likely
to include: raised floors and suspended
ceilings; basic finishes and decoration
to surfaces; and core distribution of
mechanical and electrical services to
provide basic environmental control.
Category B completes the fit-out
of the internal space to the tenant’s
requirements. This is likely to include:
the partitioning to make offices, meeting
rooms and communal areas; chosen
decorative finishes and furnishings; and
the installation of specific services to meet
the tenant’s needs – such as electrical,
lighting, IT, AV and HVAC to satisfy more
detailed environmental control.
© Tim Dwyer, 2014.
Thanks to Richard Green, of Daikin UK, for providing core information for this CPD.
- Private communication, Richard Green, Daikin UK, June 2014.
- EC Regulation 2037/2000, On substances that deplete the ozone layer, EU 2000.
- Thornton, B. and Wagner, A., Variable Refrigerant Flow Systems, US General Services Administration, December 2012.
- EC Directive 97/23/EC, The approximation of the laws of the Member States concerning pressure equipment, EU 1997.