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Thinking in multiples

Dharmesh Sawant, pointing out to the limitations of installing one VRF outdoor unit per apartment in high-rise projects, proposes the approach of multiple apartments connected to one VRF system and shares the benefits of this arrangement for stakeholders…

| | Apr 16, 2019 | 1:41 pm
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Dharmesh Sawant

I have been in the HVACR industry for 17 years and witnessed how the AC industry, in general, and Variable Refrigerant Flow (VRF) systems, in particular, have evolved over the last couple of years. The year 2008 was when the United Arab Emirates started looking at implementing sustainability in the construction industry. Dubai and Abu Dhabi were at the forefront when it came to walking the green talk, with the introduction of Green Building regulations like Estidama. MEP consultants and local developers quickly understood the social and environmental responsibility required of them and started looking at energy-efficient AC systems in their projects. That’s when everybody started looking at VRF systems as one of the obvious solutions. It still wasn’t easy-going, though. I quite vividly remember the time when I used to present VRF technology, only to hear consultants and contractors say that it would not catch up here, as the initial capex outweighed the sustainability and lifecycle costs. They were right as, initially, the cost of VRF systems was high, due to a limited number of VRF suppliers. To counter that, we as suppliers had to go to lengths to explain how VRF systems would be economical from a holistic – lifecycle cost – perspective. After years of pegging away, today, VRF systems are viewed as one of the preferred choices in low-rise apartment buildings. There is no need to explain the basics of VRF systems, as most of the consultants/developers are well-versed with the technology. But of course, we need to grow further. And for this, let us consider low- to mid-rise apartment buildings (2-12 storeys). So far, most of the developers have been showing a preference for one VRF outdoor unit per apartment. The design eliminates the number of outdoor units on the roof by 50% on an average. This means saving valuable real estate footprint in the roof-space area, lower pipe lengths between outdoor and indoor units, lower connected electrical load and lower operating cost for the tenants. However, there is a downside to it. Most of the outdoor units for such a type of application are of smaller capacity, usually adopting single compressors. Any failure in the compressor would lead to the failure of the AC system for the whole apartment. However, the probability of such an occurrence is very rare, as the inverter compressors are more stable, and there are low failure rates in tropical climatic conditions. Another drawback is that we cannot take any diversity into account with such a small capacity (7–20 kW), defeating the very purpose of the VRF technology. The situation is further compounded by the fact that lately, the higher supply in the property market and an increase in land prices are putting pressure on the selling price, and many developers are looking to go vertical. The choice of AC systems for a developer of high-rise residential buildings (12-25 storeys) is either an air-cooled chiller or a VRF system. In today’s challenging times for the construction industry, VRF becomes the obvious choice, as it offers lower capex and opex compared to its counterparts. But, as explained earlier, if we adopt the current design of one VRF outdoor per apartment, there are several limitations. Having too many outdoor units on the roof (the number of VRF outdoor = number of apartments) will put too much pressure on the designers/installers to accommodate all the utilities on the roof. Longer piping and cabling lengths will be required between outdoor units on the roof and the respective apartments, eventually increasing the piping, insulation and cabling cost. No diversity is applied, and the outdoor capacity is the same as indoor units. This leads to an overall increase in the capacity and eventually leads to increased connected electrical load. A final limitation is that there is no redundancy. The one big advantage of challenging times is that it makes the engineers think and come up with innovative ideas. In order to counter the aforementioned limitations in some high-rise projects, the proposal I wish to make is for multiple apartments to be connected to one VRF system.

Benefits for Building owners

So, what are the benefits for building owners through such an approach. Typically, they would include a reduction in the outdoor space that would need to be allotted – and this would be a 60% reduction. With this approach, instead of one VRF outdoor unit per apartment, the whole floor can be connected, and generally, these are top discharge outdoor units. The units can be located much closer to one another, compared to side discharge. The saving in the roof can provide space for a rooftop swimming pool, garden or solar panel installation. There can be a reduction in the electrical installation cost. With one whole floor connected to one VRF outdoor unit, diversity can be applied, as all the apartments and all the rooms will not operate at the same time. This offers lower connected electrical load by 10-15% compared to one VRF outdoor per apartment. This can greatly reduce the connected fee. Also, since the outdoor units are connected to the building owner’s DB, there is no need to run the power cabling between each apartment to the roof. This reduces the electrical cabling cost. This can result in lower operating cost. Annual maintenance cost for this arrangement is 15-20% lower compared to one VRF per apartment, owing to fewer outdoor units.

Benefits for contractors

The benefits for contractors would include reduction in the installation cost. Fewer outdoor units would greatly reduce the piping, control cabling lengths and number of circuit breakers. Additionally, there would be a need for fewer Sub Main Distribution Boards (SMDBs). Over and above that, the AC installation work would be much faster, with fewer outdoor units and smaller piping lengths.

Benefits for architects and consultants

The benefits for architects and consultants would include relative simplicity in design, as it would be easy for the consultants to accommodate fewer pipe risers in shafts and other services in them. And fewer outdoor units on the roof would mean a significant reduction in costs related to the civil foundation. An added benefit would be fewer challenges in deciding the electrical and piping routes.

Benefit for the end-user

The benefit for the end-user is that of redundancy. Since the whole floor is connected to one VRF system, it generally has multiple modules (3-4 per system). Even if one module fails, there would be two or more modules available to give sufficient cooling to all the apartments.

Limitation in this arrangement

There is, however, one limitation in this arrangement. The AC electricity will be billed to the building owner, since the outdoor units are connected to his DB, much like the case with a chiller. However, all VRF manufacturers have their own billing system, which helps in distributing the proportional AC electrical consumption to each tenant. The building owner also has a choice of recovering the AC consumption charges, either as a service charge or as part of the rent. A further means of mitigating the limitation could be for the authorities concerned to introduce a standard to recognise or formalise a uniform billing methodology for all VRF manufacturers.

Dharmesh Sawant is Sales Director, Hisense VRF, Qingdao Hisense Hitachi Air-conditioning Marketing Co., Ltd. He may be contacted at dharmesh.sawant@hisensehitachi.com.

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