Conventional All-air System Research Articles

Quantifying the energy flexibility potential of a centralized air-conditioning system: A field test study of hub airports

Centralized air-conditioning systems are widely considered a major energy consumer with high energy flexibility, contributing to renewable penetration and power system regulation. Nevertheless, a lack of understanding of their system components' abilities limits the utilization of their full potential. Hereby, we took the centralized air-conditioning systems of two hub airports as typical examples and quantified their energy flexibility potential by cooling load reduction potential (qmax), cooling energy storage capacity (Q), based on field test. Cooling plants had the highest potential (qmax = 70–110 Wc/m2; Q = 500∼1500 Whc/m2), followed by terminal devices with building thermal mass (qmax = 2–11 Wc/m2; Q = 10–40 Whc/m2) and transmission & distribution networks (qmax = 50–200 Wc/m2; Q = 10–20 Whc/m2). Various air-conditioning terminal devices utilize building thermal mass to different degrees. During the investigation, the conventional all-air system used 7.8 %∼18.7 % of the building's thermal capacity, whereas that of the radiant floor system significantly increased to 38.9 %∼48.3 %. Consequently, the systems of the hub airports can participate in demand response programs with a cooling load reduction of 2∼15 MWe, for 6–20 h using different operating strategies. These findings shed light on demand-side flexibility characterization and exploitation to support a decarbonized energy system.

Evaluation of the energy flexibility potential of radiant ceiling panels with thermal energy storage

This study focuses on evaluating the energy flexibility potential of an innovative cooling technology that consists of a standard radiant ceiling panel incorporating macro-encapsulated phase change materials (PCM). The incorporated PCM allows shifting the energy demand for building cooling. A simulation case study is implemented to investigate the energy flexibility of an office building conditioned by the proposed system in a hot and humid climate. At first, the thermal storage properties of the macro-encapsulated PCM were determined by using the standard ASTM C1784-20. The obtained properties were then used in a whole-building simulation model validated using measurements in a real size walk-in chamber. Three different performance indicators were used to quantify energy flexibility: available storage capacity, storage efficiency, and power shifting capacity. Results show that with an average panel to ceiling ratio of around 66%, the radiant ceiling panel has an average sensible heat storage capacity of around 430 Wh/m2day and average annual storage efficiency of 86%. Results also show that the proposed system can shift the electric power demand for conditioning by 8 h compared to a conventional all-air system. These results confirm the benefit for implementing Demand-Side Management strategies that can exploit the energy demand flexibility of radiant ceiling panels incorporating PCM.

A novel variable refrigerant flow system with solar regeneration-based desiccant-assisted ventilation

Variable refrigerant flow (VRF) based air-conditioning systems provide better thermal comfort with respect to the conventional all-air systems involving either constant air volume (CAV) or variable air volume (VAV) technique. In this study, a novel VRF strategy involving potential of improved indoor air quality has been proposed by integrating solar energy with desiccant-assisted dedicated outdoor air system (DOAS). DOAS is responsible for ventilation and humidity control. An indirect evaporative cooling arrangement is incorporated in the path of supply air from desiccant for reducing the load on the VRF system. Using Energyplus simulations, thermal and electrical energy characteristics of the proposed system have been investigated for three climatic conditions. A comparative assessment of the novel system has been made against the conventional VRF and all-air VAV air-conditioning system. Results show that for warm-humid climate, electrical energy saving potential of the proposed solar energy-assisted VRF system is around 23.9 % and 9.5 % than the conventional all-air VAV and VRF systems, respectively. Under composite climate the saving offered by the proposed system with respect to VAV and VRF is determined as 13.8 % and 9.4 %, respectively. Finally, the energy saving obtained with solar energy based VRF for the hot-dry climate is 17.5 % and 11.6 % against conventional all-air VAV and VRF systems, respectively. Excellent solar fraction is observed for composite and hot-dry climates, whereas for warm-humid climate, it is determined as 0.97. A comparative analysis with conventional cooling coil assisted DOAS-VRF system also shows energy savings by the proposed system.

Experimental evaluation of the cooling performance of radiant ceiling panels with thermal energy storage

Demand-side management (DSM) strategies in buildings generally rely on short-term heat storage in structural thermal mass. However, the thermal storage capacity is limited by the available thermal mass as buildings are increasingly built using lightweight technologies. In addition, the structural thermal mass generally has a low heat storage and release rate, limiting the ability to manage building thermal loads. To overcome these limitations, we propose an innovative, flexible cooling system that can be installed in office buildings to replace conventional all-air systems. The system utilizes the high thermal energy storage capacity of macro-encapsulated phase change materials (PCM) discreetly incorporated below the serpentine copper coil of standard radiant ceiling panels (RCP). A walk-in dual climate chamber was used to evaluate experimentally the ability of the RCP-PCM system to shift cooling loads to off-peak hours. In addition, the heat removal capacity rate and the resulting indoor thermal environment improvements are assessed. The measured passive cooling power ranged between 11 W/m2 and 31.4 W/m2, with an average of around 17.3 W/m2. Results indicate that the RCP-PCM system can shift the cooling loads to off-peak hours while maintaining acceptable thermal comfort conditions during work hours (8:00 to 18:00). During the testing period, the system was able to passively absorb heat gains between 180 and 230 Wh/m2 during the day and operate actively only at night during unoccupied periods. This load-shifting capability of the RCP-PCM system can be of great help in planning DSM strategies for increased penetration of renewable electricity in building cooling applications.

Design and control of radiant ceiling panels incorporating phase change materials for cooling applications

Experimental and numerical studies have demonstrated that thermally activated building systems (TABS) may lead to significant energy savings. However, TABS are generally incorporated into the building during the construction phase, limiting their adoption to new buildings. To encourage the application of TABS during building refurbishments, the authors have developed a radiant ceiling panel (RCP) with macroencapsulated phase change materials (PCM). This study aims to provide the criteria to design, size, and control the newly proposed RCP-PCM system. A simplified method to size and design the RCP-PCM system for cooling applications is developed from a set of parametric dynamic simulations. At first, the thermal storage properties of the macro-encapsulated PCM were determined using the standard ASTM C1784-20. The obtained properties were then used in a whole-building simulation model validated using measurements in a small test chamber that replicates the conditions of an actual test room. The PCM panel thickness of 0.015 m and a supply water temperature of 15 ℃ showed the best results in terms of thermal comfort and effective thermal energy storage capacity. The implementation of the simplified method in a case study showed that the RCP-PCM system maintained room conditions within the specified thermal comfort range (−0.5 < PMV < 0.5) for more than 90% of the occupied periods in all of the evaluated cooling-dominated climates. Moreover, yearly-round, the PMV values never reached values higher than 0.8 or lower than −0.6, confirming the effectiveness of the proposed method for designing a RCP-PCM system. The results show that energy savings of 22% could be obtained in a very hot and humid climate using an RCP-PCM system instead of a conventional all-air system. In conclusions, this paper offers a new system to promote energy flexibility and Demand-Side Management (DSM) strategies to modulate the energy demands in retrofitted buildings.

Early-design sensitivity of radiant cooled office buildings in the tropics for building performance

The research community has worked on improving the design, performance, and operation of radiant system technologies; however, the interactions between architectural design decisions and radiant cooling systems design in the tropics – where radiant system design and operation represents a challenge due to high external heat gains and latent loads – have been left unexplored by existing work. This manuscript (1) addresses the holistic early-design of effective radiant cooling systems and the architectural environments that they serve in hot and humid tropical climates, (2) analyses how different design choices and their interaction affect buildings performance compared to conventional all-air systems, and (3) proposes preliminary early-design indications of the parameters values to adopt when designing radiant cooled office buildings in the tropics to achieve high multi-objective design goals. Morris sensitivity analysis is used to analyse the impact of 13 different building and system design parameters on comfort, system and energy performances for 3 radiant systems typologies applied to a parametric office building in the tropical climate of Singapore. The elementary effect (EE) of each parameter is analysed based on 8200 individual EnergyPlus simulation models being run, and the impact, interactions & (non) linear effects of different design factors are assessed. It is found that radiant cooling systems require different early-design phase considerations than conventional air-based cooling systems since different parameters prove to be dominant or significant. All three radiant system typologies, if coupled with efficient operational strategies and a complimentary set of design variables, ensure high multi-objective building performance, showing how the implementation of radiant cooling technologies could be beneficial for a tropical climate. The window solar heat gain coefficient and the façade window-to-wall ratio play a key role in this effort with respective values falling below or equal to 54% and 57%. The system set-point temperature has an increased importance for operational efficiency allowing high dry-bulb room temperatures ranging from 24.8 °C to 27 °C.

Analysis of the energy and thermal performance of a radiant cooling panel system with integrated phase change materials in very hot and humid conditions

This study evaluates the energy and thermal performance of a radiant cooling panel system with integrated phase change materials (PCMs) for application in building retrofit projects. The focus is on the energy saving potential of using two different strategies to avoid condensation in very hot and humid climate conditions. The cooling energy consumption of a DOE medium office prototype building model with a conventional all-air system is used as a baseline for comparing the proposed configurations. The results show that the radiant system yielded energy savings of around 48% compared to the all-air system for existing office buildings. Results also show that the proposed system is able to operate only during the night-time, which improves the plant efficiency. Thus, the energy savings are mainly due to a reduction in the energy consumption of the cold generation system and lower energy use for ventilation compared with conventional air systems.

Conditioning using ceramic floor panels with capillary tube mats and solar thermal panels on the Mediterranean coast: Energy savings and investment amortisation

Radiant floor conditioning installations that distribute water through PPR capillary tube mats bring about significant energy savings and high standards of comfort. Their design usually includes air-water heat pumps and fan-coil dehumidification. They also allow incorporating solar thermal panel energy. In summer mode, they can also be combined with absorption systems with lithium bromide, or solar cold based on lithium chloride. In this way, annual energy demand is further reduced by low water channel transport and reduced heat flows through the enclosures. This study focused on the application of large-format radiant floor thermal ceramic panels (TCP), with capillary tube mats, in the Museum of the University of Alicante (MUA). The water distribution system was made of two heat pumps combined with a solar thermal panel rooftop installation. Using thermal simulation tools, the MUA's annual energy demand was quantified over various scenarios. An energy saving of 24.91% was obtained compared to conventional all-air systems, and a 60.79% saving was obtained with the use of solar panels. User comfort levels and the energy consumptions of the various elements of the installation were also comparatively quantified. To finish, we calculated the investment amortisation periods for the TCP panels and solar panels.

Performance Evaluation of Hybrid Radiant Cooling System Integrated with Decentralized Ventilation System in Hot and Humid Climates

Air-conditioning systems account for nearly one-third of the energy consumption in tropical buildings. In summer, mechanical cooling systems become a must especially in office buildings to keep the indoor environment comfort. In this study, a normal office room is designed to evaluate a novel cooling system based on a hot and humid climate. This novel cooling system is considered to serve such climate, which integrates radiant cooling panel, decentralized ventilation, and an Airbox convector. The Airbox convector is designed to deal with condensation risk and provide additional cooling output. In order to evaluate this novel system, it is compared with conventional all-air system and normal radiant system with decentralized ventilation regarding to the system capacity, energy consumption and thermal comfort. Results show that this novel system is adaptable to such climates and capable to reduce the condensation risk and overall cooling energy consumption.

Analysis on combinations of indoor thermal microclimate parameters in radiant cooled residential buildings and drawing of new thermal comfort charts

This paper proposed to discuss some issues about indoor microclimate parameters design in radiant cooled residential buildings. Based on the thermal comfort model, the relationships between low mean radiant temperature and other thermal microclimate parameters such as indoor air temperature, air velocity, and relative humidity were analyzed. The improved and reasonable combinations of four thermal microclimate parameters including radiant cooling surface temperature, air temperature, air velocity, and relative humidity were further derived. Furthermore, a number of new thermal comfort charts using radiant cooling surface temperature and air temperature as dominant parameters were drawn. The results show that the air temperature can be increased 1–3℃ within the recommended thermal comfort range when the mean radiant temperature is reduced 3℃. Under the design goal of thermal neutral, when the chilled ceiling surface temperature is in the range of 16–26℃, the air temperature should be set at 25.3–29.3℃; when the chilled floor surface temperature is in the range of 19–26℃, the air temperature should be set at 25.8–29.2℃. The design values of air velocity and relative humidity are not recommended to be changed, and still can follow the design standards for conventional all-air systems. Practical application : In this paper, some issues about indoor microclimate parameters design in radiant cooled buildings were discussed. A number of new thermal comfort charts using radiant cooling surface temperature and air temperature as dominant parameters were provided, and the design values of indoor air temperature, mean radiant temperature, air velocity, and relative humidity for radiant cooling system in residential buildings were also suggested. The research results can provide a more intuitive reference for the design of radiant cooling systems in residential buildings.

Performance evaluation of radiant cooling system integrated with air system under different operational strategies

The paper describes a study developed to estimate the energy savings potential of a radiant cooling system installed in a commercial building in India. To evaluate thermal performance and energy consumption, simulations were carried out using FLUENT and EnergyPlus software, respectively. The building model was calibrated using the measured data for the installed radiant system. Then this calibrated model was used to simulate the energy consumption of a building using a conventional all-air system to determine the proportional energy savings. For proper handling of the latent load, a Dedicated Outside Air System (DOAS) was used as an alternative to Fan Coil Unit (FCU) that was installed in conjunction with the radiant cooling system. A comparison of energy consumption calculated that the radiant system was 17.5% more efficient than a conventional all-air system and that a 30% savings was achieved by using a DOAS system compared with a conventional system. The Computational Fluid Dynamics (CFD) simulation showed that a radiant system offers more uniform temperatures, as well as a better mean air temperature range, than a conventional system. To further enhance the energy savings in the radiant system, different operational strategies were analyzed based on thermal analysis using EnergyPlus.

설비형 칠드빔 시스템 및 일반 공조 시스템 적용 공간의 온열환경 균일도 비교 평가

It is one of major objectives to achieve a uniform thermal environment and to minimize the local discomfort, when designing or operating air distribution systems. An active chilled beam (ACB) system, which is gaining much popularity owing to reduced fan energy consumption, needs to be evaluated in terms of uniform thermal environment, because it is operated with much smaller air flow rate than conventional all-air systems. The uniform thermal environment, or thermal uniformity, can be evaluated by analyzing air diffusion performance index (ADPI), local discomfort parameters within conditioned space. This study presents an evaluation method on the thermal uniformity in a room with different air distribution systems. To do this, a test bed facility was constructed so that four different air distribution systems, including ACB system, can be separatively operated. The ADPI of the ACB system was 80.7%, which is lower than that of all-air system, however, it could satisfy the recommended level (80%) of ADPI by ASHRAE. Although the ACB system resulted in the relatively low draught risk, averagely 6.7%, it was found that some regions near the chilled beam can be exposed to the draught risk due to the descending cold air. Vertical air temperature difference was not higher than , showing that the ACB system resulted in efficient air mixture in the vertical direction. It can be concluded that the ACB system can attain an acceptable thermal uniformity with much less air flow rate than other conventional air distribution systems.

Applicability of a heat and moisture transfer panel (HAMP) for maintaining space relative humidity in an office building using TRNSYS

Radiant panel systems have one of the highest technical energy savings compared to other HVAC systems and they achieve high comfort levels. However, they are unable to maintain the indoor relative humidity as they only transfer sensible heat. In order to overcome this problem, a novel heat and moisture transfer panel (HAMP) is developed and tested. In this paper, the applicability of the HAMP is tested using the TRNSYS simulation program. The impact of the HAMP on space relative humidity is investigated by modeling a one-storey office building in four North American cities (Chicago, Miami, Phoenix, and Saskatoon) as representatives of four major climatic conditions. The validity of the HAMP and resulting energy savings is represented and compared against the same building operating with two other HVAC systems: a conventional all-air system and a radiant ceiling panel (RCP) system with 100% outdoor air. The HAMP is able to control the relative humidity in the building between 25% RH and 60% RH in Chicago, Saskatoon, and Phoenix, and between 40% RH and 62% RH in Miami. The results also show the potential of the RCP system with the HAMP to reduce the total energy consumed by the conventional all-air system in different climates.

Application of radiant floor cooling in a large open space building with high-intensity solar radiation

Radiant floor cooling is suitable for environmental control in large space buildings with high-intensity solar radiation caused by a large transparent envelope. A simple method for predicting the performance of radiant floor cooling systems with solar radiation in steady state is proposed in this paper, and the key factors that influence performance are obtained. Cooling capacity of the radiant floor is significantly increased with high-intensity solar radiation and high-temperature building envelope surfaces in large space buildings. The effect of shelter of indoor furniture (such as chairs) on the performance of radiant floors is analyzed. The lowest floor surface temperature is located at the sheltered floor, and the cooling capacity of the sheltered radiant floor is also lower than that of the unsheltered radiant floor. A case study applying radiant floor cooling in a large space building is then analyzed, and the results are compared with those of a conventional all-air jet ventilation system. At the same indoor air temperature, the radiant cooling system can provide better thermal comfort at a lower operative temperature, and it presents a significant improvement in energy efficiency, with total energy demand 20–30% lower than the conventional all-air system.

Primary energy and comfort performance of ventilation assisted thermo-active building systems in continental climates

This article presents a simulation study comparing the primary energy and comfort performance of ventilation assisted thermo-active building systems (TABS) relative to a conventional all-air (VAV) system in a compact office building featuring good thermal envelope performance, heat recovery, and solar gain control for the continental climate of Omaha, Nebraska with pronounced heating and cooling periods. TABS heating is accomplished using a geothermal heat pump and TABS cooling using a geothermal heat exchanger without an additional vapor compression cycle required. It was found that the coordination of the TABS and VAV systems is crucial, i.e., supply air temperature and active layer temperature setpoints and reset schedules greatly affect the performance of the overall system. The small contribution of TABS in the heating case shows the need for the adaptation of the ventilation system configuration to the TABS system. Annual cooling energy demand for the ventilation assisted TABS is higher than for the pure VAV system, which is due to lower occupied period room operative temperatures and thus a higher comfort provided. While a 4% useful energy penalty for the combined TABS/VAV was recorded, the VAV case requires 20% more delivered energy than the TABS case because of the displacement of compressor driven coil loads with low-exergy cooling through the ground heat exchanger in the TABS case. A primary energy intensity of 189 kWh/m 2 a was recorded for the TABS case; in contrast, the conventional all-air (VAV) equipped building incurs a primary energy intensity of 229 kWh/m 2a, which represents a penalty of 20%. Clear advantages of the TABS approach can be observed with respect to thermal comfort: during summer cooling periods, the mean radiant temperature of the TABS case is on average 2 K below that of the VAV case. Moreover, the VAV system is associated with a fairly constant predicted mean vote (PMV) value of 0.75, which is quite warm, while the TABS equipped system reveals an average of 0.56, which results in only 12% instead of 17% of people dissatisfied. Based on these results, ventilation assisted thermo-active cooling systems appear to be a very promising alternative to conventional all-air systems offering both significant primary energy as well as thermal comfort advantages provided the TABS is mated with low-exergy heating and cooling sources.

A combined system of chilled ceiling, displacement ventilation and desiccant dehumidification

Different types of heating, ventilation, and air-conditioning (HVAC) systems consume different amounts of energy yet they deliver similar levels of acceptable indoor air quality (IAQ) and thermal comfort. It is desirable to provide buildings with an optimal HVAC system to create the best IAQ and thermal comfort with minimum energy consumption. In this paper, a combined system of chilled ceiling, displacement ventilation and desiccant dehumidification is designed and applied for space conditioning in a hot and humid climate. IAQ, thermal comfort, and energy saving potential of the combined system are estimated using a mathematical model of the system described in this paper. To confirm the feasibility of the combined system in a hot and humid climate, like China, and to evaluate the system performance, the mathematical model simulates an office building in Beijing and estimates IAQ, thermal comfort and energy consumption. We conclude that in comparison with a conventional all-air system the combined system saves 8.2% of total primary energy consumption in addition to achieving better IAQ and thermal comfort. Chilled ceiling, displacement ventilation and desiccant dehumidification respond consistently to cooling source demand and complement each other on indoor comfort and air quality. It is feasible to combine the three technologies for space conditioning of office building in a hot and humid climate.

Modelling of enhanced passive and conventional cooling systems

This study modelled a recently completed typical steel-framed speculative office development in the UK. It investigated the comparative performance of the building for various servicing regimes. These included natural and mechanical ventilation, two types of active fabric energy storage (FES) system (AirDeck and AirCore), air-conditioning (a conventional all-air system and chilled ceiling with mechanical ventilation), and mixed-mode solutions combining some of the above approaches. The assessment covered both summer and winter (heating) performance. The main objective was to evaluate overall performance of these systems in terms of thermal comfort and energy use and to compare the findings with more conventional servicing options for the same building. The study demonstrates that active FES can enhance thermal comfort while reducing energy use and emissions. In comparison with conventionally and naturally ventilated systems, the studied FES systems reduced temperature excess hours and peak temperatures, supplied cooler air as a result of overnight cooling, and reduced chiller consumption and boiler ratings as well as emissions. The annual operating costs of these active FES systems increase energy costs by only 13% over that of the naturally ventilated option. The mixed-mode solutions reduce them by over 35% when compared with all-mechanically cooled alternatives.

Indoor humidity behaviors associated with decoupled cooling in hot and humid climates

Radiant cooling with independent air dehumidification/ventilation is a complementary cooling and ventilation technology that has the potential to provide better thermal comfort, air quality and energy consumption than conventional all-air systems. However, in hot and humid regions, fears for the risk of condensation on ceiling panels limit its market penetration. To address this problem, in this paper, indoor humidity behaviors associated with decoupled cooling in hot and humid climates are investigated. Room mean temperature, mean humidity, maximum RH on the ceiling panel surfaces, annual condensation hours and annual primary energy consumptions are predicted with systems combining chilled ceiling with various air dehumidification and ventilation strategies, using a building energy simulation code ACCURACY. The effects of night air infiltration rates and the ratios of air flow rates of return air to those of fresh air on the indoor humidity performance and annual condensation hours are discussed. The results indicate that dehumidification and ventilation prior to cooling panels operation is required to reduce condensation risks in hot and humid climates. It is also revealed that a 1 h in advance dehumidification/ventilation in summer could completely eliminate the condensation problems.

Energy savings potential of chilled-ceiling combined with desiccant cooling in hot and humid climates

An heating, ventilating and air-conditioning (HVAC) system combining chilled-ceiling with desiccant cooling is proposed for hot and humid climates where air dehumidification is required to maintain the indoor air humidity within a comfort zone and to reduce the risk of water condensation on chilled panels. With this system, temperature and humidity control are decoupled by using desiccant wheel for moisture removal and ceiling panels for temperature control. To evaluate the system performance and the energy savings potential, another three systems: conventional all-air system, all-air system with total heat recovery, and radiant cooling with air handling unit (AHU), are considered for a typical office in Hong Kong. The hourly sensible load is calculated by a building energy simulation code ACCURACY and the latent load is predicted by moisture balance in the room. Through hour-by-hour simulations, the annual energy consumptions of the four systems are calculated and analyzed. The results indicate that chilled-ceiling combined with desiccant cooling could save up to 44% of primary energy consumption, in comparison with a conventional constant volume all-air system. More interestingly, more than 70% of annual operating hours for desiccant regeneration could be accomplished by low-grade heat of less than 80 °C.

99/03955 Thermal comfort and energy consumption of the radiant celling panel system. Comparison with the conventional all-air system: Imanari, T. et al. Energy and Buildings, 1999, 30, (2), 167–175

99/03955 Thermal comfort and energy consumption of the radiant celling panel system. Comparison with the conventional all-air system: Imanari, T. et al. Energy and Buildings, 1999, 30, (2), 167–175