High-temperature Chilled Water Research Articles

Assessment of energy saving and CO2 emission mitigation of low-lift cooling in computer hardware manufacturing industry: A case study in Thailand

Abstract Released heat from production process contributes the largest proportion of cooling load in computer hardware manufacturing industry. According to traditional design practice, chiller plant produces chilled water at a temperature of 7°C to treat the entire load from the production process and from the comfort air-conditioning in buildings. However, the heat from the process is solely the sensible component where high-temperature chilled water (e.g., 15°C) can be used for the heat removal, the chillers equipped with low temperature-lift technology thus offer a great opportunity to improve the plant’s cooling performance. Under the critical global warming situation and the need of decarbonizing industry, this paper investigated the energy saving and CO2 emission mitigation potential of the low-lift technology by which the chiller plant of high-temperature chilled water (15°C) is dedicated for the production process cooling, and the traditional chiller plant of the low-temperature chilled water is used to serve the building air-conditioning. The study site was a large factory of computer hardware manufacturing in Thailand. Through detailed energy auditing, the cooling load profile of the production process was established, and it was used to design the low-lift chiller plant. The annual simulation results showed that in our study case the low-lift chiller plant together with variable motor speed control had 31.6% higher cooling performance than the traditional chiller plant. The plant could reduce the energy consumption by 5,550 MWhelec/year. As the CO2 emission of the grid power in Thailand was 0.47 kgCO2/kWh in 2023 and it was expected to reduce to 0.35 kgCO2/kWh in 2050, the CO2 emissions from implementing the low-lift cooling could be reduced by 49,400 TonCO2 over a course of the 20-year project lifetime. The study results encouraged the low-lift cooling technology as a practical energy efficiency measure in computer hardware manufacturing industry. To our knowledge, while past research focused on the low-lift cooling in building air-conditioning, the study was the first potential assessment project of the low-lift cooling as a deep decarbonization technology for the computer hardware manufacturing industry in Thailand.

Experimental study on the operating characteristic of the desiccant cooling systems with the potential of condensing heat recovery

The requirement for extra regeneration heat is a significant issue limiting the energy efficiency of desiccant cooling systems. To avoid the additional energy consumption, this study analyses two systems that use condensing heat to regenerate the desiccant. The experiments for the heat pump-assisted type are executed at different indoor load profiles. A comparative experiment is carried out on a water loop-assisted type. Experimental results show that the heat pump-assisted type obtains a maximum regeneration temperature of 40.4 °C and a minimum supply air humidity ratio of 3.5 g/kg DA at the outdoor temperature below 26 °C. However, the thermal imbalance problem leads to uncontrollable indoor temperatures under 50 W/m2 load conditions. The proposed operation mode automatic switching control can improve indoor temperature by switching the system between dehumidification and cooling modes. Compared to the heat pump-assisted type, the water loop-assisted type has the same dehumidification capacity and a more stable indoor thermal environment control using high temperature chilled water above 14 °C and reduce the total primary cooling energy consumption by 58%. This study analyses the feasibility of recovering condensing heat from the perspective of thermal energy analysis, and expands the research on desiccant cooling systems without extra regeneration heat sources.

Analysis of a low-temperature small approach open cooling tower integrated with radiant cooling and displacement ventilation for space conditioning in temperate climates

ABSTRACT Evaporative cooling, using cooling tower systems, has the potential to offer an alternative approach for producing high temperature chilled water, particularly for buildings located in temperate climates. The current paper examines the performance of an integrated cooling system, where an open forced draught counter flow cooling tower is used for the provision of chilled water for a radiant cooling and displacement ventilation system. For this purpose, a low temperature low approach direct evaporative cooling tower is used which can provide cooling water with low approach temperatures (1-3 K), which defines the temperature difference between the tower water outlet temperature and ambient wet bulb temperature. The performance of the proposed cooling system has been investigated for internal buildings loads up to 66 W·m-2 in order to examine the limitations of the cooling system. Space thermal comfort conditions and system performance metrics were assessed for four different temperate climate types as follows: cool and dry (Helsinki), cool and semi-humid (Birmingham), warm and dry (Prague), and warm and humid (Paris). The assessment shows that for the proposed system, where a radiant floor was used, can provide acceptable thermal comfort conditions for approximately 80% of the occupant hours over the respective cooling seasons.

The performance of a desiccant wheel air conditioning system with high-temperature chilled water from natural cold source

A novel desiccant wheel air conditioning system that uses high-temperature chilled water from natural cold source (DWACS + HCW) is proposed. The proposed system integrates the renewable regeneration heat source and natural cold source, which are beneficial for energy saving. A model of the proposed system was developed, and the main components and the overall model were experimentally validated. The performance and the effects of the important parameters of the system under high humidity (32 °C, 80% RH), moderate humidity (32 °C, 60% RH) and low humidity (32 °C, 40% RH) conditions was studied numerically. The results showed that the system could achieve the supply air to the required temperature and humidity ratio in high, moderate and low humidity conditions, and compared to conventional solar desiccant wheel air conditioning systems (SDWACS), the energy performance is more efficient mainly due to high cooling and dehumidification capacity of surface air-cooler with high temperature chilled water.

Exergy and energy analysis of a novel dual-chilling-source refrigerating system applied to temperature and humidity independent control

This paper proposed a novel dual-chilling-source refrigerating system using R407C applied in the temperature and humidity independent control system. The theoretical model was established to analyze the performance of this system regarding the coefficient of performance, exergy loss and exergy efficiency in comparisons with a single-chilling-source refrigerating system. The results showed that the dual-chilling-source refrigerating system had obvious advantages over the single-chilling-source refrigerating system. The dual-chilling-source refrigerating system improved the coefficient of performance and exergy efficiency by about 25% and 30%, respectively, and decreased exergy loss by around 25%. The outdoor relative humidity had the most significant effects on the system exergy loss. With the outdoor relative humidity increasing from 40% to 90%, the exergy loss value was increased by about 43% and 42% for the single-chilling-source refrigerating system and dual-chilling-source refrigerating system, respectively. The effects of low-temperature chilled water temperature on the coefficient of performance, exergy loss and exergy efficiency were more remarkable than those of high-temperature chilled water temperature. Overall, the dual-chilling-source refrigerating system had significant potential in saving energy and improving exergy efficiency, especially for the high humidity load area.

High efficiency ‘low-lift’ vapour-compression chiller for high-temperature cooling applications in non-residential buildings in hot-humid climates

Over the last decade, building engineers have begun implementing sensible-latent de-coupled air-conditioning systems in non-residential buildings in hot-humid climates. Typically, a de-coupled system consists of a dedicated outdoor air sub-system for ventilation and high-temperature radiant cooling sub-system for space cooling. This approach has lowered cooling energy demands and fan energy consumption in buildings. However, the complete energy saving potential of de-coupled systems, specifically high-temperature space cooling sub-systems, can only be realized by using low-lift chillers that supply chilled water which matches the high-temperature radiant cooling application.This paper discusses the results of a retro-installation of a prototype modular low-lift chiller to provide high-temperature chilled water (at 17 °C) to the radiant cooling units. The paper presents temperature and cooling load profiles, control methodology and energy efficiency improvements of the low-lift cooling system. The paper also further discusses the influence of various parameters on the performance of the chiller. Despite having a cooling capacity of only 20 kW, the modular low-lift chiller is consistently able to achieve a Coefficient of Performance (COP) of 8. By operating at a low-lift (20 K) compared to a high-lift (29 K), the sensible cooling electrical consumption (at the chiller) is reduced by 23% despite being compared to a high-lift low-temperature chiller with 100 x higher cooling capacity. When normalized for cooling capacities, this reduction is between 29–30%. The project is the first known installation of low-lift cooling for building comfort control in hot-humid climates, and first reported publication of low-lift cooling in a real-life scenario - i.e., non-laboratory conditions or modelling exercise.

Efficient Operation of Heat Source using High-temperature Chilled Water in an Advanced Office Building

In recent years, energy conservation has become a major focus in the industrial sector. Many office buildings in Japan achieve energy savings by introducing highly efficient equipment and systems, such as high-temperature cooling water (14 °C), which increases heat source efficiency. However, such equipment requires adjustments to increase operational efficiency. In this case study, the efficiency of equipment using high-temperature cooling water was further improved through operation control optimization. The energy efficiency before and after the improvement was compared. The target building has chilled and hot water supplied to each floor from district heating and high-temperature chilled water supplied from cooling chillers on the rooftop. The energy consumption of two floors was evaluated: a subjective floor with equipment using high-temperature cooling water installed, and a common floor with a conventional system. After on-site verification, changes were made to the operation control of the cooling towers, condenser pumps, primary pumps, secondary pumps, and air handling units. As a result, the coefficient of performance of the water-cooled chiller and the whole system improved by 0.40 and 0.45, respectively. The flow rate of the air conditioning equipment using high-temperature cooling water decreased while maintaining an equivalent amount of heat extraction. In conclusion, the efficiency of the equipment was further improved by operation control optimization.

Entransy analysis on the performance of the counter-flow heat exchangers for a double evaporating temperature chiller

The double evaporating temperature (DET) chiller has been considered as a credible method to realize temperature and humidity independent control (THIC). Energy performance optimization is of great significance for the extensive application of the DET chiller. In this paper, entransy method is employed to analyze heat transfer performance of heat exchangers based on the extremum principle of entransy dissipation (EPED) and the minimum entransy dissipation-based thermal resistance (EDTR). The entransy dissipation rate and EDTR are discussed in detail to indicate the impacts of tl,c, th,c (i.e., temperature of low temperature chilled water, high temperature chilled water), MC(R32): MC(R236fa) (i.e., mass concentration ratio of R32 to R236fa), and structural parameters on heat transfer performance of heat exchangers. The results indicate that the lowest entransy dissipation rate of heat exchangers are achieved when MC(R32): MC(R236fa) is 40%: 60%. The design tl,c/th,c are suggested to be set at 7/16 °C to reduce the entransy dissipation rate and EDTR of heat exchangers, which is beneficial to strengthen energy utilization of the chiller for energy saving. Considering the significant effect of heat capacity ratio of two steams on the EDTR, mr (i.e., mass flow rate of refrigerant) and ml,c/mh,c/mc (i.e., mass flow rates of low/high temperature chilled water/cooling water) should be increased and decreased, respectively.

Exergy and energy analysis of a double evaporating temperature chiller

Temperature and humidity independent control (THIC) has been demonstrated as an effective way to improve the performance for air-conditioning systems. As an alternative option of THIC method, a double evaporating temperature (DET) chiller using zeotropic mixture refrigerants of R32 and R236fa has been proposed to substitute the traditional water-cooled chiller. The low temperature chilled water of 7 °C and high temperature chilled water of 17 °C will be produced simultaneously by this DET chiller, and the latent and sensible cooling loads of buildings can be afforded by the produced low temperature chilled water and high temperature chilled water respectively. In this paper, the experiments with different concentration ratios of R32 to R236fa are carried out on a 4.0-kW DET chiller. To further improve the energy performance of the DET chiller, the exergy analysis is used to investigate the effects of chilled water temperature and mass concentration of zeotropic mixture on the DET chiller. The exergy loss for each component is discussed in detail to identify the inefficient components, and then indicate the ways to improve the performance of DET chiller. The results show that the DET chiller achieves the lowest exergy loss and highest exergy efficiency when the mass concentration ratio of R32 to R236fa is 40%: 60%. Furthermore, the design temperature of high temperature chilled water should be at 16 °C to improve the energy utilization of DET chiller. This study will help to understand the design and operation for the DET chiller based air-conditioning systems.

Evaluation of low-lift sensible cooling in the tropics using calibrated simulation models and preliminary testing

This article addresses an opportunity to improve Low Exergy air-conditioning system efficiencies in the tropics by incorporating ‘low-lift’ chillers. This paper builds on the 3for2 Project in Singapore, the region's lowest energy consuming office. Using calibrated energy models, laboratory measurements of the low-lift chiller and preliminary on-site testing, the performance of a low-lift chiller was studied in relation to a high-lift chiller. The paper concludes that the complete energy saving potential of high-temperature radiant cooling panels can be realized only if the high-temperature chilled water is produced directly by a low-lift chiller. The preliminary indicate that the peak and annual aggregate of radiant sensible cooling can be reduced by 22.8% and 13.5%

Experimental and theoretical study on a novel double evaporating temperature chiller applied in THICS using R32/R236fa

A novel chiller with double evaporating temperatures is proposed in this paper, which can be applied in temperature and humidity independent control system (THICS). A zeotropic mixture R32/R236fa is selected as the refrigerant, and chilled water with two different temperatures is produced. The experimental coefficient of performance (COPexp), theoretical coefficient of performance (COPth), and second law efficiency (η) of the chiller are studied. The performance of the chiller is studied by varying the mass fraction of R32 in the R32/R236fa (W(R32)), chilled water temperature, and the flow rates of the heat transfer media (chilled water and cooling water). The results show that the high temperature chilled water (TH,out) can be at 15–18 °C, and the low temperature chilled water (TL,out) can be at 6–8 °C. When TH,out is 17 °C and TL,out is 7 °C, the maximum COPth and COPexp are 4.73 and 3.97, respectively. Second law efficiency, η, increases to 31% as W(R32) increases from 0.3 to 0.6.

Performance comparison of temperature and humidity independent control air-conditioning system with conventional system

The energy consumption of centralized air-conditioning systems represents a large percentage of total building energy consumption in commercial buildings. The temperature and humidity independent control system, regulating indoor temperature and humidity separately through different approaches, is a feasible improvement to conventional systems. This paper focuses on the performance discrepancies between the temperature and humidity independent control systems and the conventional systems. A typical office building in Guangzhou is chosen for case study and energy performances of three temperature and humidity independent control systems with different outdoor air handling processes are investigated. Compared to the conventional system, energy efficiency ratio for the entire air-conditioning season of temperature and humidity independent control system I using condensing dehumidification is about 10% higher if the dry fan coil unit is adopted; of temperature and humidity independent control system II with high-temperature chilled water for precooling is about 16% higher, and energy efficiency improvement of temperature and humidity independent control system III with heat pump driven liquid desiccant air handling processor is about 22%. For other three cities in China, the energy saving ratio of temperature and humidity independent control system I is about 10%, about 15%–17% of temperature and humidity independent control system II and 20%–23% of temperature and humidity independent control system III. Practical application: THIC air-conditioning system is supposed to be an effective approach for energy saving in buildings. Chosen a typical office building as an example, this paper gives the energy performance discrepancies between the conventional system and the THIC systems for researchers and designers. Annual energy consumptions for different air-conditioning systems are compared, and the energy saving ratios of THIC systems are obtained. The research will be helpful for designing and constructing an energy efficient central air-conditioning system for buildings. In these typical cities or cities with similar climate, THIC system III with the highest energy efficiency is recommended just from the perspective of energy saving.

Performance analysis of a low approach low temperature direct cooling tower for high-temperature building cooling systems

For certain temperate climate types, cooling towers have the potential to produce high temperature chilled water, which when used in conjunction with radiant and displacement cooling technologies, have prompted interest in this concept as a potential approach for the conditioning of buildings. The feasibility of the proposed system depends largely, on achieving low approach water temperatures within an appropriately designed cooling tower, at acceptable levels of energy performance. Using a validated mathematical model, the current paper examines the performance of such a cooling tower for four different temperate climate conditions. The current assessment shows for building water return temperature of 22°C, for temperate climates that are considered warm and humid, the limitations on cooling tower operation are when ambient conditions exceed 25°C and 75% RH. Two strategies were investigated to allow the smallest practicable approach to the wet bulb temperature to be achieved: (i) increasing the tower air flowrate, (ii) decreasing the tower water flowrate. For a temperate climate that is warm and humid, operating the cooling tower with an approach of 1.0K was found to be not practicable for all encountered weather conditions, but use of a 2.0K approach was found to be practicable for all conditions.

On-site measured performance of a radiant floor cooling/heating system in Xi’an Xianyang International Airport

In large space buildings such as airports, radiant floor systems are an attractive alternative to conventional all-air jet ventilation systems due to their advantages in thermal comfort and energy efficiency. This paper focuses on the operating performance of the radiant floor system in Terminal 3 of Xi’an Xianyang International Airport, the first airport terminal in China to adopt radiant floors for cooling. In summer, the typical cooling capacity of the radiant floor is 30–40W/m2 with a mean chilled water temperature of 18°C; this range increases to 110–140W/m2 with solar radiation of 120–170W/m2. The incremental effect of the solar radiation on the cooling capacity of radiant floor is analyzed with simple calculation methods. In winter, the radiant floor provides a heating capacity of 30–70W/m2 with a hot water temperature of 35–40°C, which is sufficient to satisfy the heating requirement. Compared with the jet ventilation system adopted in Terminal 2 of the same airport, indoor thermal comfort is significantly improved with the radiant floor system in Terminal 3 in both cooling and heating modes. Moreover, the novel system’s indoor air temperature distribution throughout the whole space and its utilization of high-temperature chilled water and low-temperature hot water reveal its potential for energy conservation.

Mathematical modeling of a low temperature low approach direct cooling tower for the provision of high temperature chilled water for conditioning of building spaces

Recent interest in cooling towers, as a means of producing chilled water in conjunction with radiant systems for cooling in buildings, has prompted interest in evaporative cooling in temperate maritime climates. For such climates, evaporative cooling has the potential to offer an alternative approach to refrigeration-based air-conditioning systems for producing chilled water, where conventional refrigeration-based systems can, for certain buildings, be considered to be an over engineered solution and where passive cooling is insufficient to offset cooling loads. The thermal efficiency of evaporative cooling systems is a key performance indicator, as a measure of the degree to which the system has succeeded in exploiting the cooling potential of the ambient air. The feasibility of this concept depends largely however, on minimizing the approach water temperatures within an appropriate cooling tower, at acceptable levels of energy performance. Previous experimental work for a full scale evaporative cooling system has shown that it is possible to produce cooling water with low approach temperatures (1–3 K), at the higher temperatures required in radiant and displacement cooling systems (14–18 °C), with varying levels of annual availability for different temperate climate locations. The current paper is concerned with the development of a mathematical model which describes the behavior of such a low temperature low approach direct evaporative cooling tower. The mathematical model is evaluated against experimental data reported for a number of open tower configurations, subject to different water temperature and ambient boundary conditions. It is shown that the discrepancies between the calculated and experimental tower outlet temperatures are to within ±0.29 °C for a low temperature cooling water process (14–18 °C), subject to temperate climate ambient conditions and ±0.57 °C for a high temperature cooling water process (24–30 °C), subject to continental climate ambient conditions. Considering the associated tower cooling loads, predicted results were found to be within a 6.93% root-mean-square difference compared to experimental data. Furthermore, the influence of different cooling tower coefficients on water outlet temperature and heat rejection of tower is investigated.

The feasibility of performing high-temperature radiant cooling in tropical buildings when coupled with a decentralized ventilation system

In Singapore's hot and humid environment, air conditioning has moved from being perceived as comfort to now being a necessity. Buildings usually employ large energy-consuming air systems to condition interior spaces. The use of water-based high-temperature cooling concepts is hard to find due to fears of condensation. The objective of this research is to enunciate the decentralized approach adopted in performing space cooling and dehumidification. The experiment aims at understanding the practicability of using radiant panels with high-temperature chilled water for accomplishing sensible cooling coupled with an independent ventilation system for achieving latent dehumidification. The dew point temperature of air surrounding the radiant panels is monitored to check for condensation. The decentralized ventilation system tested was effective in reducing absolute humidity in air from 22.3 g/kg in outside air to 12.8 g/kg at the under-floor air distribution system's diffuser outlet. The associated dew point temperature and dry bulb temperature measured at the diffuser outlet was 13.9°C and 19.9°C (57°F and 67.8°F), respectively. The measured dew point temperature of air surrounding the radiant panels was 18.3°C (64.9°F), which demostrates the viability of operating radiant panels using high-temperature chilled water to achieve sensible cooling. The air exchange effectiveness of the system running at low supply air velocity was determined to be 1.12, which demonstrates a displacement ventilation system. The air change rates measured per hour using tracer gas techniques ranged between 0.9–2.2 when the supply fan speed was varied between 4000–8000 rpm. The amount of outdoor air thus supplied to the designed space ranged between 0.9–2.1 L/s-m2 (assuming the system ventilation efficiency as 1). These values are above 0.7 L/s-m2, which is the minimum requirement for ventilating office spaces according to Singapore standards.

Performance analysis on a residential radiant chilled ceiling system and evaluation on indoor thermal environment in summer: an application

The performance of a residential radiant chilled ceiling system combined with an outdoor air handling unit under steady operating conditions in summer was tested, and the stable operating characteristics of this system were analyzed. Indoor thermal environment parameters of room which employed this system were measured and analyzed and the thermal comfort evaluation of occupants was given. The results show that the composite system works well in summer, which can provide low- and high-temperature chilled water for the air supply terminal and the radiant terminal devices. Good thermal comfort can be achieved in room which employed this system, and no condensation risk occurs when it is applied in hot summer and cold winter zone of China. All the analysis provides a technical support for the popularization of the residential radiant chilled ceiling system combined with an outdoor air handling unit in China, and provides a reference for the further optimization of this system.

In situ performance of independent humidity control air-conditioning system driven by heat pumps

A liquid desiccant based independent humidity control (IHC) air-conditioning system driven by heat pumps is presented in this paper. The system consists of a liquid desiccant fresh air processor and a high-temperature chilled water system. The operating principles of the fresh air processor and the whole system are presented in detail. Based on the in situ system installed in an ecological building of Shanghai Research Institute of Building Sciences (SRIBS), a performance investigation was performed in summer, 2007. The measurement results show that (1) the indoor temperature and humidity both are in the specified range; (2) the supply water temperature of the high-temperature refrigerator is higher than the corresponding indoor air dew point temperature, so no condensed water would be formed on the fan-coil unit (FCU) surface; and (3) the average coefficients of performances (COPs) of the fresh air processor and the high-temperature refrigerator are 6.24 and 4.38, respectively, and the average COP of the whole IHC system is 5.28.

Environmental Systems at Walt Disney World

Walt Disney World constructed and operates all utility systems within its property. Particularly unique systems include AVAC, which is a pneumatic solid waste collection system, generation of electricity using aircraft-type jet engines, high temperature hot water and chilled water derived from the waste heat of the jet engines, utilidors throughout the high density area of Theme Park for utility mains, Neyerpic gates to automatically regulate water levels in canals and lakes, and sewage effluent disposal on a tree farm.