Many a times, I come across the statement that VRF technology is only suitable for villas and low-rise buildings. On further probing, I realised that the market is driven by this perception, because it is common practice to locate the condensing units on the roof to hide the so-called ugly-looking units and not to disturb the beautiful glass façade, typical of so many buildings in the GCC region. Therefore, the common understanding is that it is not feasible to use VRF technology in high- rise towers (G+30 and above) for the following reasons…
- The increase in cost in running the insulated refrigerant pipe from individual floors to the roof
- The increase in cost in running the power cable from each apartment to the roof
- The increase in the capacity to counter the piping deration
- Reduced space on the roof for the condensing unit, as the roof is narrow for high-rise towers, making it difficult to accommodate all the services.
Owing to the above reasons, the client usually turns to a chiller system and, by doing so, relinquishes the opportunity of benefiting from the following features inherent in a VRF system…
- Lower total CAPEX (15-20% lower than a chiller system)
- Direct individual billing between the utility and the tenant – in the case of buildings with a chiller system, many owners are finding their electricity bill increasing year on year with the increase in electricity tariff and slab-wise tariff.
- Ease in retrofitting – a chiller retrofit needs a heavy crane for lifting the unit to the roof
- Lower connected electrical load (25~30%)
With all the above-facts placed in front of you, now what if there is a way out by which we can utilise the above benefits by eliminating the limitations of the VRF system for high-rise buildings. Bingo!
My colleagues and I precisely did that in a project we were awarded recently. The project in question was a G+35 residential building in Wadi Al Safa. The consultant team comprised Archgroup Consultant and Consistent Engineering Consultant (CEC). The contractor was International Electromechanical.
This project was initially designed to accommodate a chiller system. The building owner had his concerns relating to the operating cost, though. Typically, buildings with a chiller system are connected to the owner’s DB (Distribution Board). This means the tenant doesn’t have to pay for the electrical consumption of air conditioning; it is understood to be included in the rent. This leads to over consumption of the air conditioning system. The rent depends on the market forces, and might increase or decrease, but the electricity consumption keeps on increasing year after year due to ageing of the equipment and to the increase in the electricity tariff, as a chiller system always falls in the highest slab of 38 fils/KWh.
At the same time, the owner wanted to reduce the project’s capital expenditure. The obvious solution was to go for a VRF system, but the increase in the piping and cabling cost and the deration due to piping loses increased the overall cost of the project. Also, the compact roof space made it difficult to accommodate all the condensing units. The owner gave flexibility to the architect for amending the design to meet the intent.
The Architect, MEP Engineering Consultant, and LG went back to the drawing board to find out space on each floor for accommodating the
condensing unit. The architect came up with the idea of utilising a dead space on each floor to accommodate the outdoor units. For proper heat exchange, they covered it with Mashrabiya (an architectural feature that emerged in Egypt, it is a type of projecting window, enclosed with delicately carved wood latticework).
The next issue was to make sure that there was no heat-island effect, as there were four outdoor units in each utility room, and we wanted to put to rest any doubt of short-circuiting of the hot air from one floor to another.
LG conducted the CFD analysis through 3D-modelling and concluded that a flat louvre with a maximum angle of 20 degrees will not cause any tripping or overheating of the condenser unit. The result of the CFD analysis is as follows…
As a result of the initiative, the client could get the following benefits…
- Saved vertical run of 37,000 metres total refrigerant piping (gas and liquid). This also made the shaft free of any refrigerant pipes.
- Saved vertical run of 18,500 metres of power cable
- Saved 10% deration in the capacity due to short piping length
- Saved 1,130 kilogrammes of R-410A refrigerant due to elimination of vertical riser from the shaft (additional refrigerant charge – 0.061 Kg/m, the total liquid pipe eliminated was 18,500 metres)
- Increased life and better performance of the condensing unit, as it is not exposed to the direct sunlight and dust
- Direct billing from DEWA (utility provider) to tenant, eliminating the need for third-party billing
The success of the project was possible only because of the following…
- The flexibility shown by the architect in creating a balance between aesthetics and utility
- The innovative and forward-thinking approach of the MEP consultant, CEC. They could foresee the potential problems in the design stage, and LG responded by clearing those concerns through undertaking CFD analysis and a feasibility study.
- Close-knit teamwork and coordination involving the architect, MEP consultant, manufacturer (LG) and the MEP contractor
Dharmesh Sawant is Senior Manager – HVAC Engineering 1 Team at LG Electronics MEA. He can be contacted at firstname.lastname@example.org.
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