A museum storeroom air-conditioning system employing the temperature and humidity independent control device in the cooling coil

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Abstract

For conservation of cultural heritage, HVAC systems are often necessary for museums to maintain suitable indoor environment with precise control of indoor thermal-hygrometric parameters and air velocity. Large deviations of these parameters from the design values should be prevented, because they may cause degradation of artworks. So, more energy consumption is inevitable.

This paper presents a novel temperature and humidity independent control (THIC) device and its associated control method in a museum storeroom air-conditioning system. Compared with the conventional HVAC system with the cooling coil (CC), where the apparatus dew point is usually fixed, this system adopting the THIC device can achieve independent temperature and humidity control in an energy saving way. The experiment study shows that this system can reduce the energy consumption by 21.7%, compared with the conventional HVAC systems using reheat and humidify for an indoor thermal-hygrometric environment, and the temperature and humidity in the storeroom are also kept stable and at a higher precision level.

Highlights

► A temperature and humidity independent control (THIC) device for cooling coils is developed. ► The THIC device can achieve independent temperature and humidity control with higher precision. ► Reliable PID-based control logic for the THIC is developed. ► The THIC device can save running energy consumption by about 20–30%.

Introduction

Conservation of artworks requires precise control of the indoor microclimatic conditions. Thus, a suitable HVAC system with reliable control is often necessary for a museum, to maintain acceptable indoor thermal-hygrometric parameters and air velocity and also to minimize the deviations of these parameters from the design values. So it is indispensable for the museum air-conditioning system to comprise heating, humidifying, cooling, dehumidifying and automatic control units to control the temperature and humidity at the same time. Considering that the HVAC system in museum always has to be operated continually during all the year and 24 h per day, a suitable technique is necessary to obtain considerable energy saving [1], however, guaranteeing a good indoor thermal-hygrometric microclimate. It is shown by some literatures [2], [3], [4], [5] that the energy consumption will be reduced by about 10–50%, if the HVAC system adopts a suitable energy-saving technique.

For conventional HVAC system, customarily, the dew point temperature is fixed on the cooling coil (CC) in the air-handling process, which makes the air after the CC be over-cooling to guarantee both the temperature and the humidity ratio are lower than the supply air parameters, and then results in much more energy compensation for reheating and re-humidifying. To reduce that compensation, it is necessary for the CC to reduce the over-cooling capacity, so the temperature and humidity independent control (THIC) technique has been studied in many literatures. Generally, substituting desiccant dehumidification for cooling dehumidification in the CC, the THIC technique uses solid desiccants [6], [7], [8] or liquid desiccants [3], [9], [10], [11]. But how to realize independent control of temperature and humidity in the same cooling coil in HVAC system is a worthwhile problem, and there are few literatures about this THIC technique.

In this paper, an HVAC system employing the THIC device in the CC is proposed and designed. With the PID split-range control, only one of the two air thermal-hygrometric parameters after CC, i.e. temperature or humidity ratio, is to be controlled below the supply air, in order to make the over-cooling capacity as little as possible. And some experiment tests were done to validate the THIC device.

Section snippets

THIC device

The THIC device presented in this paper can be used in the CC of both existing and new conventional HVAC systems, as shown in Fig. 1.

Fig. 2 shows the schematic diagram of the THIC device. For temperature control, the CC adjusts the mass flow rate of the chilled water according to the sensible cooling load; and for humidity control, it adjusts the temperature of the chilled water according to the dehumidification load, or the latent load. Before and after the CC, an electric controllable

Experiment setup

An HVAC system employing the TIHC device was manufactured and installed to air-condition a museum storeroom, the main parameters are listed in Table 1. It comprises the following subsystems: (1) AHU with a CC, a heater, a humidifier and a constant flow rate fan, and the details of the CC are listed in Table 2; (2) Air distribution duct system; (3) A storeroom (22 m × 16 m × 4 m) equipped with the HVAC system in order to maintain the suitable thermal-hygrometric parameters for cultural heritage

Results and discussion

Table 3 shows the experimental results of 5 cases under different indoor heat loads but the same temperature and relative humidity of the storeroom (22 °C, 60%). When the storeroom temperature and relative humidity was fixed, the parameters of the supply air should be adjusted along with the change of storeroom heat load. The working conditions are listed as follows:

Objective temperature and relative humidity of the storeroom:22 °C, 60%
Ambient temperature and relative humidity:25 °C, 76%
Flow

Conclusions

For saving energy of the HVAC system, a temperature and humidity independent control (THIC) device is proposed in this paper, and the THIC device is implemented in a real HVAC system for a museum storeroom. Through the experiment and analysis, some conclusions can be drawn as follows:

  • (1)

    The THIC system can guarantee both the temperature and the relative humidity of the conditioned storeroom are at a higher precision level under different working conditions.

  • (2)

    The THIC device ensures that only two of

Acknowledgements

The research work presented in this paper was supported by a research grant (A-PJ13) in the Hong Kong Polytechnic University, the Major State Basic Research Development Program of China (973 Program) under contract No. 2011CB706501, and the third batch subsidies of the Zhejiang provincial cultural relic protection in 2008 (No. 614841).

References (11)

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