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Experimental evaluation of the ventilation effect on the performance of a VRV system in cooling mode--part I: experimental evaluation.

Article Excerpt
INTRODUCTION

Air conditioning and ventilation for residential and commercial buildings are highly demanded due to concerns of thermal comfort and healthy environment of the living space in modern society. A multi-split air-conditioning system, featuring variable refrigerant volume (VRV) technology--the so-called multi-split VRV system--with one outdoor and several indoor units, is finding its way into residential and commercial buildings since it provides precise capacity control with an inverter-driven compressor and individual electronic expansion valves (EEVs) for each indoor unit. Since the first multi-split VRV system was installed more than 20 years ago in Asia (Goetzler 2007), this technology has been widely studied experimentally (Xia et al. 2002; Masuda et al. 1991; Hai et al. 2006; Hu and Yang 2005; Choi and Kim 2003; Zhou et al. 2007a, 2007b; Watanabe et al. 2004) and numerically (Wu et al. 2005; Xia et al. 2003, 2004; Shi et al. 2003, 2008; Park and Min 2001; Zhou et al. 2008; Shah et al. 2004; Shao et al. 2008). Previous studies mostly focused on control strategies of the variable-speed compressor and EEVs. It was observed that the compressor frequency and the EEV openings should be controlled simultaneously (Masuda et al. 1991; Hu and Yang 2005; Choi and Kim 2003; Wu et al. 2005; Shi et al. 2003; Shah et al. 2004; Lin and Yeh 2007). On the contrary, it was also claimed that the major control parameter was the EEV opening (Park and Min 2001). In addition to the studies related to the control strategy, the performance of the multi-split-type systems has been investigated (Hai et al. 2006; Shi et al. 2003; Park and Min 2001).

Despite the large number of previous studies, there is not an operational study under varying outdoor conditions except the work by Aynur et al. (2006), which did not consider the effect of ventilation on the performance of the multi-split VRV system. Since the multi-split VRV systems cannot provide any ventilation required by ASHRAE regulations (Goetzler 2007), additional ventilation systems are necessary to be installed. This is why the integration of the multi-split VRV system and the ventilation system gains importance in actual applications. In this study, a field performance evaluation of a multi-split VRV system integrated with a heat recovery ventilation (HRV) system is investigated experimentally under varying outdoor conditions.

EXPERIMENTAL SETUP AND INSTRUMENTATION

Experimental Setup

Two multi-split VRV systems and four HRV units were installed in an actual office suite for the field performance measurements. The layouts of the multi-split VRV and HRV units in the office suite are provided in Figures 1a and 1b, respectively. As can be seen from Figure 1a, System1 consisted of outdoor unit 1 (OU1) and indoor units located in the zones of Rooms A, B, C, and D, served to the southern side of the floor. System2 consisted of outdoor unit 2 (OU2) and indoor units located in the zones of elevator, receptionist, aisle, and Room E, served to the northern side of the floor. OU1 and OU2 are identical and consist of two compressors, one of variable speed and one of fixed speed. The indoor temperature control was performed by individual thermostats located in each zone. The detailed information can be obtained for the internal load sources from Aynur et al. (2007). The catalog data of the outdoor unit and indoor units of the multi-split VRV system are provided in Table 1. As can be seen from Figure 1b, two HRV units, HRV1-1 for Rooms A and B and HRV1-2 for Rooms C and D, were used for ventilation of the southern side. Two additional HRV units, HRV2-1 for elevator, receptionist, and aisle and HRV2-2 for Room E, were used for the ventilation of the northern side of the office suite. The total ventilation rate for the office suite was determined based on ANSI/ASHRAE Standard 62.1-2007, Ventilation for Acceptable Indoor Air Quality, (ASHRAE 2007) for a maximum expected occupancy profile, and each...

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