Consulting-Specifying Engineer - January 2009 - (Page 16) M/E/P Roundtable Smith: Ventilation requirements are application driven and as such there is no standard practice for meeting the ventilation requirements. Every solution is different, but with VRV/VRF systems, there are plenty of options even before separate systems are considered. For example, many of the indoor fan coil units can easily accept outside air and deal with the requirements of the space, and manufacturers offer OA processing units or ERV that tie in seamlessly to the VRV/VRF systems. If separate ventilation systems are incorporated, there are also options as to how much or how little they actually tie into the VRV/VRF system, with a solution being to use the VRV/VRF system to condition the space and the separate ventilation system just providing constant ventilation air. CSE: How easy are VR systems to install, operate, and maintain? What makes them harder or easier to maintain than chilled water (CHW) or rooftop unit (RTU) systems? Agulles: Some people claim that VR systems are no more difficult to install than a typical DX split system. For the systems installed without heat recovery capability, that is a fair statement, except that you need to pay more attention to how the joints and connections are piped. On the refrigerant piping side, VR systems can be a little less forgiving than conventional systems. For systems with heat recovery, some contractors do not have much experience dealing with the branch controller/selector component of the system. There are also some nuances regarding how different VR manufacturers put their systems together that can be tricky for an installing contractor. For example, some of the heat recovery systems are threepipe systems; others are two-pipe systems. Some controllers require a condensate drain connection; others do not. I think that the manufacturers realize that the success and growth of VR systems, in terms of proliferation into the U.S. market, is partially dependent on good support for the contractor community. As far as maintenance, with VR systems, the user has distributed equipment with multiple, smaller compressors to maintain, rather than few, large centralized compressors in a chiller plant. With VR systems, there are no pumps in the system to be maintained. In comparison to a RTU system, VR systems have distributed fan coil units to maintain, including filters and fans rather than a series of VAV boxes within the space. From an ongoing operations standpoint, there are two important factors that come into play with VR systems. One is equipment life; the second is replacement equipment and parts. With good maintenance, central chiller plants can have an operational life of 25 years or longer. VR systems have a shorter operational life, closer to 15 to 20 years. Unlike central chilled water systems, with VR systems, you are making a longterm commitment to one manufacturer. Components are not interchangeable among different manufacturers. After a system is installed, parts and replacement equipment must come from the same manufacturer. Brantley: VR systems utilize modular outdoor units, unlike large package equipment. The systems do not require balancing like chilled water or VAV systems. Soft copper can be used throughout the system for easier installation. The entire control system is a simple twowire installation. Finally, VR manufacturers offer system installation and startup training to ensure the highest level of quality from the very beginning. Smith: A VRV/VRF system is delivered to site with the installation 80% complete. The installing contractor takes the factory engineered components and places them in the necessary locations and joins everything together from a piping, electrical, and communications perspective. To simplify the piping process, pipe sizes are provided with drawings furnished for the equipment, and special refrigerant fittings are also provided to reduce the amount of field piping manipulation required on-site. Minimal test and balancing is required, and commissioning is commonly an automated function built into the VRV/VRF system. Operation is simple in that each zone can be in control of its own mode and temperature via a simple-to-use LCD controller. As the system comprises DX type equipment, the normal maintenance cycle consists of a simple cleaning of filters and condensing unit heat exchangers. Roy: I agree that the primary advantage for these systems is the ease of installation. The evaporator units are typically mounted in a lay-in ceiling with a cassette-type unit or mounted side wall in the space. The only connections are the two or three refrigerant pipes, depending on cooling only or heat/cool units, a condensate drain, and a power feed from a nominal 208V/1 phase circuit. The primary disadvantage of VR systems is substantially higher maintenance resources for the distributed evaporator units in terms of filter changes, blocked condensate drains, etc. However, the distributed units are also one of the many benefits of the system in that system failure is usually limited to the area served by the evaporator units. Failure of the condensing unit is an equal burden to centralized systems such as at an RTU or chiller unit. In virtually every maintenance aspect, the modular design of a VR system allows for quick and efficient replacement of component failures. Web extra: For extended interviews, additional questions, and participants, visit www.csemag.com 16 Consulting-Specifying Engineer • JANUARY 2009 http://www.csemag.com
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