Moisture transport processes and control of relative humidity in refrigerated facilities : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering at Massey University, Palmerston North, New Zealand

Increasingly air relative humidity (RH) is becoming an important design and operational variable for refrigerated facilities. An integrated dynamic model of the main heat and moisture transfer mechanism in a refrigerated facility was developed. Specific features of the model that enabled RH to be predicted were: • Multiple air zones to represent variation of temperature and RH with position. • A single zone evaporator model with dehumidification based on a straight line approach to the saturation condition at the surface temperature. • Condensation and evaporation of water from surfaces and structures in the facilities. • Evaporator defrost assuming that a fraction of the defrost heat melts frost and the rest heats the evaporator and refrigerant mass. • Hot gas bypass with liquid refrigerant desuperheating to prevent the compressor operating into vacuum. • Moisture sorption by packaging associated with the product. The model was validated against data collected from a walk-in cool store 3.3m wide by 4.4m long by 3.0m high. The cool-store was cooled by an air cooled direct expansion HFC-134a refrigeration system with electric defrost, a suction line heat exchanger and electronic evaporation pressure regulating (EPR) valve for temperature control. To mimic the different design and operating conditions extra sensible and latent heat loads were provided by the cool store lights, up to 5 kW of electric heaters, and an ultrasonic humidifier. For the validation room trials fan speed, coil size, sensible load, latent loads and temperature set point were varied. Other conditions were held constant as far as possible and the room was operated for at least two defrost cycles. For the coolstore the model computed about 70 ordinary differential equations and more than 160 algebraic equations which were solved using Matlab 6.5, with the ODE45 solver. The measured and predicted store air temperature, RH, refrigerant suction and discharge temperatures and pressures showed good agreement for most of the trials during both pull-down and the mainly steady-state operation between defrosts. Differences in measured and predicted RH and refrigeration system operating conditions were largely explained by uncertainty in model input data, measurements and calibration; and imprecision of the actual refrigeration control system and particularly the hot gas bypass capacity control and the expansion valves. This suggests that the model is a useful tool for the design and optimisation of passive or active RH control strategies for refrigerated stores. Trials were also undertaken to quantify the effect of defrost frequency on the coolstore performance. Defrost efficiency and defrost duration were both proportional to defrost interval and doubled as defrost interval increased from 6 hours to 30 hours. For short defrost intervals; temperature control was poorer due to the frequent pull-downs. For longer defrost interval the room RH was lower and temperature control was poorer due to frost induced decline of evaporator performance The optimal defrost interval for the particular cool store was 8 to 12 hours. Overall energy use did not change significantly due to the use of EPR temperature control and the low latent heat loads used

Ceiling-fan-integrated air conditioning: Airflow and temperature characteristics of a sidewall-supply jet interacting with a ceiling fan

Ceiling-Fan-Integrated Air Conditioning (CFIAC) is a proposed system that can greatly increase buildings’ cooling efficiency. In it, terminal supply ducts and diffusers are replaced by vents/nozzles, jetting supply air toward ceiling fans that serve to mix and distribute it within the room. Because of the fans’ air movement, the system provides comfort at higher room temperatures than in conventional commercial/ institutional/retail HVAC. We have experimentally evaluated CFIAC in a test room. This paper covers the distributions of air-speed, temperature, and calculated comfort level throughout the room. Two subsequent papers report tests of human subject comfort and ventilation effectiveness in the same experimental conditions. The room’s supply air emerged from a high-sidewall vent directed toward a ceiling fan on the jet centerline; we also tested this same jet on a fan located off to the side of the jet. Primary variables are: ceiling fan flow volumes in downward and upward directions, supply air volume, and room-vs-supply temperature difference. Velocity, turbulence, and temperature distributions are presented for vertical and horizontal transects of the room. The occupied zone is then evaluated for velocity and temperature non-uniformity, and for comfort as predicted by the ASHRAE Standard 55 elevated air speed method. We show that temperatures are well-mixed and uniform across the room for all of the fan-on configurations, for fans both within or out of the supply jet centerline. The ceiling fan flow dominates the CFIAC airflow, and even though non-uniform is capable of providing comfortable conditions throughout the occupied area of the room

Thermography and Sonic Anemometry to Analyze Air Heaters in Mediterranean Greenhouses

The present work has developed a methodology based on thermography and sonic anemometry for studying the microclimate in Mediterranean greenhouses equipped with air heaters and polyethylene distribution ducts to distribute the warm air. Sonic anemometry allows us to identify the airflow pattern generated by the heaters and to analyze the temperature distribution inside the greenhouse, while thermography provides accurate crop temperature data. Air distribution by means of perforated polyethylene ducts at ground level, widely used in Mediterranean-type greenhouses, can generate heterogeneous temperature distributions inside the greenhouse when the system is not correctly designed. The system analyzed in this work used a polyethylene duct with a row of hot air outlet holes (all of equal diameter) that expel warm air toward the ground to avoid plant damage. We have observed that this design (the most widely used in Almería’s greenhouses) produces stagnation of hot air in the highest part of the structure, reducing the heating of the crop zone. Using 88 kW heating power (146.7 W∙m−2) the temperature inside the greenhouse is maintained 7.2 to 11.2 °C above the outside temperature. The crop temperature (17.6 to 19.9 °C) was maintained above the minimum recommended value of 10 °C

A study of the actual airflow over a physical conical tensile membrane model

Knowledge of the airflow pattern and rate in and around fabric membrane structures is still relatively unknown compared to the existing knowledge of more conventional structures. This paper reports qualitative wind tunnel experiments, which were conducted using a number of physical models representing a simple conical membrane structure. Horizontal, inclined, open and closed apex cases were explored for a variety of cone rise/diameter ratios and apex height/diameter ratios. Monitoring of the air velocity was carried out on a grid of 84 different points for each configuration. In this paper only six of the cases monitored in the wind tunnel are reviewed. Using these results, the possible use of a conic tensile membrane structure’s topology and orientation to enhance ventilation rates and airflow velocities within the covered space is discussed. It is concluded that there is a need for further research in this area, in order to fully realise the potential benefits offered by tensile membrane structures for modifying airflows in their vicinity

Decay of airborne contamination and ventilation effectiveness of cleanrooms

This article reports an investigation into the ability of the air supply in non-unidirectional cleanrooms to aid recovery from episodes of airborne contamination, and minimise airborne contamination at important locations. The ISO 14644-3 (2005) recovery test, which measures the rate of decay of test particles, was assessed and a reinterpretation of the test results suggested. This allowed air change effectiveness indexes to be calculated and used to evaluate the ventilation effectiveness of the cleanroom’s air supply. Air change effectiveness indexes were measured in various designs of cleanrooms, and reasons for deviations in the value of the indexes investigated

Aerodynamic effects in ink-jet printing on a moving web

This work was sponsored by EPSRC grant number RG5560

Environmental scrutiny of traditional Mediterranean forms for contemporary application (an empirical study)

Traditional architecture has successfully created a desirable indoor environment with minimal energy consumption and compatible with social and cultural contexts. The proper use of environmental passive design strategies that were widely employed in regional, traditional and vernacular architecture is crucial. However, employing traditional architecture vocabularies within contemporary buildings requires a proper understanding of their forms’ environmental-behaviors. Consequently, modifying forms, geometries, and design-concepts may enhance their environmental performance. On the same time such traditional forms will stand for architectural identity that appropriately serves environmental, cultural and social contexts. A building that respects cultural and social beliefs of the people is believed to address more practically the issue of sustainability. The undertaken review and investigation in this paper seeks a better understanding and application of traditional architecture forms and geometries in Egypt’s northern-coast contemporary architecture. The investigations highlight the methodological approach carried out, to seeking a better understanding of the thermal and solar performance of these traditional passive systems regardless of their construction materials and colors. This is done, as a contribution towards improving their physical qualifications and energy efficiency performances. Furthermore, the paper is a low-energy architecture approach for more energy efficient and passive buildings (particularly low-rise buildings) in the new communities that are being developed recently in Alexandria, Egypt and other hot-arid parts. Therefore, it establishes an architectural approach to resist the rapid growth of international styles and produce an environmentally, culturally, and socially appropriate architecture. In order to verify whether these forms are environmentally and climatic sound quantitative analysis needs to be carried out. The paper is part of continuing research work carried out on certain traditional roof forms. This is discussed through empirical and experimental tests for number of traditional forms (domes, vaults and cones) in the contemporary built environment of Alexandria city and Egypt’s northern-coast. The paper focuses on the methodology and approach used in the analysis of the chosen forms

Effects of Air-Injection Pressure on Airflow Pattern of Air Sparging

Air sparging is a remediation technology for treating soil/groundwater contaminated with volatile organic compounds (VOCs). VOC removal during air sparging is rendered less effective because of the random formation of air channels, creating preferential paths for airflow, thus limiting remediation to these channels, referred to as a zone of influence (ZOI). Pulsation is a popular method used to improve the effectiveness of air sparging through cyclic operation, with the hope that air channels would form elsewhere. Pulsation makes air sparging more time-consuming. This paper studies the effects of one cycle of pulsation and air pressure on the airflow pattern and presents a laboratory study that investigated the effects of initial and further increases in the injected air’s pressure on the airflow pattern within a glass-bead medium used as a medium analogous to the soil. Digital images of airflow patterns were collected; these images show a larger radius of influence (ROI) and ZOI due to the initial air-pressure increase, particularly when a higher overburden pressure (i.e. the stress due to the partially saturated layer on top of the saturated soil-simulant layer) exists above the water-saturated zone. Further air-pressure increases seem to have no measurable effect on the ROI and the shape of the ZOI