All-air System Research Articles

Energy saving potential of fresh air pre-handling system using shallow geothermal energy

To reduce the energy consumption for fresh air handling, a novel fresh air pre-handling system that fully exploits the shallow energy to precool and preheat fresh air is proposed in this study. The model of a typical all-air system with a pre-handling system is built on the TRNSYS platform. The energy saving potential of this fresh air pre-handling system is simulated based on the diverse climate of China. The results show that the ratios of the cumulated heat transfer capacity of the fresh air pre-handling system to the annual total of cooling and heating load range from 35% to 45% in the temperate zone and the subtropical zone, such as Shenyang, Beijing, and Shanghai, while the ratio in the tropical zone is approximately 10%. The energy saving rates are approximately 30% in most climate zones, but less than 5% in Guangzhou, the tropical climate zone. Moreover, the payback periods are within 4 years in the temperate and subtropical zones. However, the system is not economical in the tropical zone. All these results indicate that the fresh air pre-handling system with shallow geothermal energy is quite promising in most climate zones except in the hot summer and warm winter region with a tropical climate.

Energy and thermal comfort performance evaluation of PCM ceiling panels for cooling a renovated office room

The performance of suspended ceiling panels with phase change materials (PCM) for comfort cooling applications in office rooms was studied. The panel consisted of a metal casing, which encapsulates the PCM. Water can circulate through the pipes embedded in the panel to influence the latent energy storage of the material. To evaluate the performance of the PCM panels, a comparison with an all-air system and a thermally active building system (TABS) was made. Using TRNSYS 17, a recently renovated room in the Technical University of Denmark was modelled. The room was simulated during the cooling season with each of the three cooling systems in which the thermal environment and the corresponding energy use were determined. Operative temperature was maintained between 22°C to 27°C at least 90% of the occupied period with each system. Similarities were observed between the PCM and TABS systems. Energy savings of 15% and peak cooling power reduction of 30% compared with the all-air system were observed. This study proved the common claim that PCM ceiling panels and TABS perform similar in terms of the created thermal indoor environment and energy savings, as well in terms of heat removal from the indoor space. Therefore, PCM ceiling panels could be used as an alternative for TABS in renovation projects while providing similar benefits to TABS.

Side-by-side laboratory comparison of space heat extraction rates and thermal energy use for radiant and all-air systems

Radiant cooling systems extract heat from buildings differently than all-air cooling systems. These differences impact the time and rate at which heat is removed from a space, as well as the total amount of thermal energy that a mechanical system must process each day. In this article we present measurements from a series of multi-day side-by-side comparisons of radiant cooling and all-air cooling in a pair of experimental testbed buildings, with equal heat gains, and maintained at equivalent comfort conditions (operative temperature). The results show that radiant cooling must remove more heat than all-air cooling – 2% more in an experiment with constant internal heat gains, and 7% more with periodic scheduled internal heat gains. Moreover, the peak sensible space heat extraction rate for radiant cooling (heat transfer at the cooled surface, not the cooling plant) must be larger than the peak sensible space heat extraction rate for all-air systems, and it must occur earlier. The daily peak sensible space heat extraction rate for the radiant system was 1–10% larger than for the all air system, and it occurred 1–2 hours earlier. These findings have consequences for the design of radiant systems. In particular, this study confirms that cooling load estimates for all-air systems will not represent the space heat extraction rates required for radiant systems.

Energy analysis of a hybrid radiant cooling system under hot and humid climates: A case study at Shanghai in China

A conventional radiant panel system offers advantages in terms of energy savings; however, compared with an all-air system, it has limitations such as moisture condensation risk, slow air movement, difficult space zoning, slow air pollutants removal from a highly polluted room, and time delay in start-up of the radiant panel system. This research performs an energy consumption analysis of a hybrid radiant cooling system for buildings in summer. The hybrid radiant cooling system combines a typical radiant panel with a decentralized air convector connected in series. The hybrid radiant panel system generates additional cooling output through its air convector, dehumidifies indoor air, increases indoor air movements, and reduces the time delay in start-up and a filter in the air convector removes air pollutants. This study exhibits the energy performance of the hybrid radiant cooling system compared with an all air system and a typical radiant panel system via numerical modeling using experimental data. This hybrid radiant panel system is effective for energy-saving, because it has a higher cooling impact ratio, and larger coefficient of performance of the chiller, and because the air movement increases the offset effect of the operation indoor temperature rise by an enhanced mixed convection effect. Thus it can reduce cooling energy consumption. The hybrid radiant cooling system can be used very effectively for saving energy in the summer season.

Comparing temperature and acoustic satisfaction in 60 radiant and all-air buildings

There is little knowledge from occupied buildings of the impact of radiant heating and cooling systems on indoor environmental quality aspects such as thermal comfort, indoor air quality, and acoustics. We present indoor environmental quality survey results from 3892 respondents in 60 office buildings located in North America; 34 of which used all-air systems and 26 of which used radiant systems as the primary conditioning system. In the current study, we present the survey results of 1645 occupants in buildings with radiant systems. To our knowledge, this is the largest dataset used in a comparison of occupant satisfaction in radiant buildings. We used an existing database to extract a subset of occupant responses from all-air buildings whose key characteristics match those radiant buildings. The results indicate that radiant and all-air spaces have equal indoor environmental quality, including acoustic satisfaction, with a tendency towards improved temperature satisfaction in radiant buildings.

Thermal and ventilation performance of combined passive chilled beam and displacement ventilation systems

Chilled beams provide sensible cooling to an occupied space by using chilled water flowing through modular beams mounted to a room ceiling. Previous studies show that active chilled beam systems can achieve larger sensible cooling than all-air systems. However, most studies have focused on active chilled beams and little information is available for performance of passive chilled beam (PCB) under varied ventilation conditions. The objective of the present study is to investigate ventilation and air conditioning performance of combined PCB and displacement ventilation systems. Using a validated and verified computational fluid dynamics (CFD) model, parametric analyses were performed to examine the ventilation and air conditioning performance depending on five major operating parameters: 1) ventilation strategy, 2) PCB cooling output, 3) supply air temperature, 4) supply diffuser type, and 5) internal heat source arrangement. The results show that thermal comfort and ventilation performance of a combined PCB-DV system notably vary with the PCB cooling output and supply air temperature. When the PCB cooling output increases from 33% to 53% of the total cooling load, air change effectiveness decreases from 1.6 to 1.2 and vertical temperature difference decreases from 4.0°C to 1.5°C in the breathing zone. However, spatial heat source distribution has a marginal effect on the air mixing and temperature distribution. The results suggest that a relatively high PCB cooling output (>50% of the total cooling) combined with a low supply air temperature (e.g., 17°C) could disrupt thermal stratification of displacement ventilation and increase draft rate in the occupied zone.

Operational performance of an Air Handling Unit: insights from a data analysis

Space heating and cooling is one of the most relevant causes of energy consumption in both residential and tertiary sector buildings. In particular, service buildings and offices are mostly served by all-air HVAC systems in which control logics are fundamental to guarantee reliability and performance. Building automation systems are therefore becoming more and more relevant as a support tool for reducing the energy consumption in these contexts. For this reason, the detailed analysis of operational data from real units can help in understanding the main variables that affect the performance and functioning of all-air systems. This paper presents some results from operation data analysis of an Air Handling Unit (AHU) serving a large university classroom. The main drivers of the energy consumption are highlighted, and the classroom occupancy is found to have a significant importance in the energy balance of the system. The availability of historical operation data allows performing a comparison between the actual operation of the AHU and the expected performance from nominal parameters. An example of fault detection is proposed, considering the operation analysis of the heat recovery unit over different years.

Thermal Ceramic Panels and Passive Systems in Mediterranean Housing: Energy Savings and Environmental Impacts

This research examines the benefits of designing a living space in a basement, as a method of passive temperature control in summer, combined with thermal ceramic panels (TCP) on some walls. These panels incorporate a capillary system of polypropylene tubes which work with cold water. We studied a detached house on the coast of Alicante, where the moderate temperature of the ground tempered interior conditions of comfort using the flow of air from the basement, significantly reducing energy demand and environmental impacts. This reduction was quantified through simulations using the Design Builder tool, having previously monitored the state of the building, on scenarios of a house without a basement, a house with a basement and an all-air system, and a house with a basement and radiant surfaces, using TCP panels on walls. This latter passive system led to a 10.25% reduction in annual energy demand. When we combined it with the two possible air conditioning systems, comfort achieved using the TCP panel system improved by 45.8% compared to the all air system in the living room on the ground floor and by 17% in the basement living room. In addition, annual energy demand and environmental impacts deriving from the use of the installation decreased by 31.8% with the TCP system.

New hybrid system combining TEG, condenser hot air and exhaust airflow of all-air HVAC systems

One of the most promising solution for the current energy crisis is recovering lost energy. Indeed, in many energy systems the percentage of energy loss could exceed 60%. To put it another way, in some applications, recovering energy is as much beneficial as finding new source of energy. Moreover, finding new concepts of energy recovery offers wider horizons to reduce energy consumption. The present work investigates new energy recovery system that combines heat recovery and energy generation using thermoelectric generators (TEG). The proposed system is a triple Thermoelectric-Energy recovery coupled system that from one hand allows to recover the heat of condenser and to reuse the lost energy of exhaust airflow of HVAC all-air system and from the other hand it permits to produce green electricity using TEG. The air of the condenser is considered the heat source, whereas the exhaust air flow is utilized as cooler. To proceed, a mathematical tool is first developed it allows to thermally simulate TEGs for different boundary conditions. The heat and cold source are then modeled where the heat transfer coefficient is determined from the Nusselt number. Furthermore, a parametric analysis is then conducted to evaluate the power generated with the new concept when the air velocity of the exhaust airflow and that of the condenser vary. It is shown that for a space cooling load of 100kW, a 40×40cm2 flat plate is capable to generate 90W of electrical power.

Modeling and simulation of a photovoltaic/thermal air collector assisting a façade integrated small scale heat pump with radiant PCM panel

Integration of photovoltaic/thermal air-based systems into office façade retrofit projects using small scale decentralized heat pumps with low temperature short term storage using a radiant phase change material panel (RPCMP) is presented for a south facing office building perimeter zone. The concept can be applied in building façade retrofits, where both façade and mechanical systems are to be replaced. A numerical study is carried out for a case study building in Saskatoon, Canada. A numerical model is developed and the concept is theoretically compared to an all-air system for several consecutive design days. Electric power demand reduction of 14,5% for these design days can be achieved, if the façade integrated photovoltaic system would be supplying energy to the perimeter zone for heating and plug load applications. A reduction in heating coil heating power demand of 11.3% is achieved for the mentioned design days when compared to an all-air system.

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.

Cerámica y climatización saludable: paneles cerámicos radiantes en edificios. Condiciones de confort y demanda energética frente a sistemas convectivos

El gres porcelánico es un material ampliamente utilizado en edificación. En los últimos años su uso ha experimentado un nuevo espectro de líneas de innovación e invención en sus aplicaciones en la arquitectura. En esta investigación de analiza la patente Panel de Acondicionamiento Térmico Cerámico, consistente en piezas de gres porcelánico de bajo espesor, que contienen tramas capilares a base de tubos de polipropileno de 3,5 mm de diámetro, e interfaz de pasta conductora. Estos sistemas trabajan con agua fría o caliente produciendo una climatización saludable por superficies radiantes. Tras una primera experiencia de prototipado y colocación de paneles en pared en un despacho de oficina, se han realizado simulaciones en el Museo de la Universidad de Alicante, colocando los paneles en pared, techo o tipo bafle, previa monitorización del estado actual del edificio. Se han analizado los parámetros de comportamiento térmico y se han comparado con otros materiales de acabado habituales. Se han obtenido resultados de confort térmico y ahorros energéticos de forma comparativa frente a sistemas todo-aire.

Thermal comfort in buildings using radiant vs. all-air systems: A critical literature review

Hydronic radiant heating and cooling systems are considered as an energy efficient technology to condition buildings. We performed a literature review to assess if radiant systems provide better, equal or lower thermal comfort than all-air systems. We included only peer-reviewed articles and articles published in proceedings of scientific conferences. The publications found have been classified based on research methods used. These include: (1) building performance simulation (BPS), (2) physical measurements (in laboratory test chambers and in buildings) and (3) human subject testing/occupant based surveys. This review identified eight conclusive studies: five studies that could not establish a thermal comfort preference between all-air and radiant systems and three studies showing a preference for radiant systems. Very few studies were based on occupant feedback in real buildings suggesting a significant research need. Overall, we found that a limited number of studies are available and therefore a solid answer cannot be given. Nevertheless, there is suggestive evidence that radiant systems may provide equal or better comfort than all-air systems.

Retrofitting building fire service water tanks as chilled water storage for power demand limiting

Peak demand cost usually contributes a large proportion of the total electricity bills in buildings. Using existing building facilities for power demand limiting has been verified as effective measures to reduce monthly peak demands and associated costs. Fire service water tanks exist in most commercial buildings. This paper presents a comprehensive study on how to effectively retrofit existing building fire service water tanks as chilled water storage for power demand limiting. Important technical and economic factors that may affect the implementation of the proposed retrofitting are addressed. Two retrofitting schemes, i.e. a small ΔT (storage temperature difference) scheme and a large ΔT scheme are proposed for integrating the chilled water storage system into an existing all-air system and an existing air-water air conditioning system, respectively. Two optimal demand limiting control strategies, i.e. time-based control and demand-based control, are proposed for maximizing the monthly peak demand reduction of buildings with regular and variable peak occurring time, respectively. The cost-effectiveness of different retrofitting schemes in three real buildings in Hong Kong is analysed. Results show that substantial cost savings can be achieved with short payback periods (0.7–2.6 years) for the retrofits in these three buildings. Practical application: This paper presents a techno-economic analysis on retrofitting existing building fire service water tanks as chilled water storage for power demand limiting and operational cost saving. The proposed retrofitting schemes and demand limiting control strategies enable chilled water storage systems to be readily applied to most existing buildings. Building owners can benefit from the peak demand cost saving as the monthly peak demand can be significantly reduced by using chilled water storage. The extra costs involved in tank retrofits and system integrations can be paid back within three years.

Energy renovation of an office building using a holistic design approach

This paper presents a holistic approach to perform energy renovations of office buildings. A real case study is used to demonstrate how different software can be used to facilitate the work of architects and engineers during different design stages. Initially, the moisture safety of the building is coupled to its energy performance to define the optimum insulation level. The new interior layout is based on an initial daylight study, rather than on architectural intuition. On a second stage, shading and natural ventilation are studied to eradicate any cooling demand, while the interdependence between heating energy and daylight is assessed for the use of light-wells. To demonstrate the trade-offs between visual control and electrical lighting, different shading systems are examined for a cellular office. Finally, two alternate HVAC systems are analyzed to investigate whether passive standards can be achieved with an all-air system and/or a hydronic system.

Cooling Performance Comparison of Radiant Floor System and All-air System with Solar Radiation

In large space buildings such as airports, convention centers and entrance halls, the e velope is dominated by glass facades and skylights, and the indoor thermal enviro ment is characterized by high-intensity solar radiation. The heat transf r process of radiant floor and air system are compared in this paper. During the cool ng process, radiant floor removes indoor heat not only by convection but also by radiation, while air system handles all the heat by circulating ai. It means that radiant floor can absorb the solar radiation directly. A case study comparing radiant floor and air system is analyzed, and the results show that with transient high-density solar radiation, radiant cooling system can enlarge the terminal cooling apacity more remarkably than air system. The adaptivity of radiant cooling system can help avoiding temperature fluctuations and prevent unnecessary indoor adjustment requirements.

IEA EBC Annex 59 - Possibilities, Limitations and Capacities of Indoor Terminal Units

Indoor terminal units can be defined as the building elements that use different heat transfer mechanisms and media to emit and remove heat or moisture from indoor spaces (e.g. hydronic radiant heating and cooling systems, fan-coil units, active beams). Indoor temperature and humidity fields depend on the chosen terminal units.Terminal units differ in their capabilities of addressing sensible and latent loads, methods of heat emission or removal, maximum heating and cooling capacities, medium of energy distribution, and local or total volume conditioning.In the present study, operation characteristics, possibilities and limitations of different terminal units were specified. Considered terminal units were radiant heating and cooling systems, all-air systems (mixing, displacement, and personalized ventilation), passive and active beams. The results were summarized in a table, which aims at providing a reference for terminal unit selection during the design phases of HVAC systems.

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.