Outdoor Fresh Air Research Articles

Design and analysis of a BIPV/T system with two applications controlled by an air handling unit

A building integrated photovoltaic thermal (BIPV/T) system was designed and analyzed. The BIPV/T system is composed of multiple PV/T air collectors integrated into the building facade and connected to an air handling unit (AHU) to control the air flow. The system operates with two applications, an application for cold weather and an other for hot weather. In cold weather, the BIPV/T system recovers heat from the PV modules to preheat the outdoor fresh air. While in hot weather, the cool air exhausted from the conditioned spaces of the building is used to decrease the PV cells temperature, instead of ambient air as in conventional PV/T air collectors. An experimental tests were conducted to see the effect of using the cool exhaust air as coolant for the PV cells instead of ambient air. In order to predict thermal and electrical performance of each PV/T air collector under real climatic conditions, a theoretical model of a single pass PV/T air collector was developed and validated against experimental observations from previous literature. The theoretical and experimental comparison between the case of using exhaust air as coolant and the case of using ambient air as coolant showed an important decrease in PV cells temperature. The maximum decrease value in PV cells temperature obtained from the simulation is 9.46°C in a selected day from August, while the electrical simulation showed that the average increase value in electrical efficiency in a selected day from August is 0.350. The simulation of the BIPV/T system in cold weather indicated that the average rate of saved useful thermal energy when using preheated outdoor fresh air in a selected day from February is 24.20%. Furthermore, the PV/T air collector performances were compared for the optimal tilt angle and the complete vertical position. The results revealed that installing the PV/T air collector at optimal tilt angle showed much better performances than a one installed at a complete vertical position, especially the electrical performance in Summer.

A study on variation laws of infiltration rate with mechanical ventilation rate in a room

Mechanical ventilation system is commonly used or recommended to supply the outdoor fresh air for both centralized and non-centralized air-conditioning buildings. ASHRAE requires a positive pressure (i.e., zero infiltration rate) for mechanically ventilated rooms. In fact, positive pressure is difficult to be maintained under poor building airtightness or low mechanical ventilation rates. When the positive pressure is not achieved, the existence of air infiltration brings two problems—the outdoor air pollutants infiltrating indoors and the excessive fresh air cooling/heating load. In order to solve the above problems, air purifiers can be used to remove the indoor pollutants, and the mechanical ventilation rate should be reduced to prevent the excessive ventilation. Therefore, in order to determine the Clean Air Delivery Rate (CADR) for the air purifier and to calculate the amount of mechanical ventilation that should be reduced, the influence of mechanical ventilation on the room infiltration rates must be figured out. This study investigates the variation laws of the infiltration rate with the mechanical ventilation rate, and then theoretically deduces the relational expressions between the two rates for stack effect and wind dominant ventilation models. The theoretical derivations were validated by tests in actual rooms. From a practical perspective, this study can be used to improve the indoor environment and ventilation rates for mechanically ventilated rooms, demonstrated by the case study.

Development of a CFD model for simulating vehicle cabin indoor air quality

As the level of CO2 within the vehicle cabin increases, the risk of accidents as a result of driver drowsiness and a slowing of the reactions also increases. Accordingly, a CFD simulation model was developed in this study to explore the effects of outdoor air ventilation rate on vehicle cabin indoor air quality and the amount of outdoor air required for each person in a vehicle. The results show that using the outdoor air supply rate recommendations of ASHRAE Standard 62.1 (i.e. 2.5 l/s per person) the mean CO2 concentrations in the cabin are around 2850 ppm. The results also show that using the outdoor air supply rate recommendations of 4.0 l/s per person for improved human wellbeing, the corresponding mean CO2 concentrations in the cabin are around 1810 ppm. Moreover, the present study found that an outdoor fresh air flow rate of 9.2 l/s per passenger was sufficient to reduce the carbon dioxide concentration within the cabin to a safe value of 1000 ppm. Furthermore, an outdoor fresh air flow rate of 3.6 l/s per passenger resulted in a carbon dioxide concentration of around 2000 ppm.

Performance evaluation of a photovoltaic thermal-compound thermoelectric ventilator system

External fixed shading devices are generally used to adjust solar influx radiation and save energy in summer. However, they could block the beneficial solar radiation in winter. In this paper, a photovoltaic thermal-compound thermoelectric ventilator (PVT–TEV) system is proposed and investigated. The PVT–TEV system not only could prevent direct solar radiation from going into buildings in summer, but also could heat fresh air by the air-type PVT coupled with a thermoelectric ventilator system in winter. A PVT–TEV system was built in a room for testing the system. Results demonstrate that the performance of the PVT–TEV system is mainly affected by solar radiation when the system works in the sunny days of winter. The stronger the solar radiation is, the more the heat of PVT–TEV system gains and the higher the fresh air temperature is. The average electrical efficiency of PVT is 10%, the average thermal efficiency of PVT–TEV is 26.7% and the average COPh of PVT–TEV is 6.4. In the rainy day, the outdoor fresh air is heated when it flows through heat pipe exchangers of the thermoelectric ventilator. The higher the working voltage is, the more the heat TEV system gains and the lower the COPh of the TEV system is. The average COPh of PVT–TEV system is 1.73 when the operating voltage is 24 V. The PVT–TEV system provides an active and green method for building exterior shading device and supplying fresh air.

Improving indoor air quality and thermal comfort in office building by using combination filters

Poor indoor air quality and thermal comfort condition in the workspace affected the occupants’ health and work productivity, especially when adapting the recirculation of air in heating ventilation and air-conditioning (HVAC) system. The recirculation of air was implemented in this study by mixing the circulated returned indoor air with the outdoor fresh air. The aims of this study are to assess the indoor thermal comfort and indoor air quality (IAQ) in the office buildings, equipped with combination filters. The air filtration technique consisting minimum efficiency reporting value (MERV) filter and activated carbon fiber (ACF) filter, located before the fan coil units. The findings of the study show that the technique of mixing recirculation air with the fresh air through the combination filters met the recommended thermal comfort condition in the workspace. Furthermore, the result of the post-occupancy evaluation (POE) and the environmental measurements comply with the ASHRAE 55 standard. In addition, the level of CO2 concentration continued to decrease during the period of the measurement.

Energy Saving Potential of Hybrid Liquid Desiccant and Evaporative Cooling Air-conditioning System in Hong Kong

Abstract The hybrid liquid desiccant dehumidification and evaporative cooling system, short for LDD-EC system, is regarded as a promising energy-saving air-conditioning (A/C) scheme for hot and humid regions. Unlike most previous reported LDD-EC system based on traditional indirect evaporative cooler (IEC) and 100% fresh air system, the LDD-EC system with partial circulation air was explored by fully making use of dry return air from air-conditioned space. The regenerative indirect evaporative cooler (RIEC) is used to sensibly cool the return air. The outdoor fresh air is firstly dehumidified in the LDD unit to have the latent heat removed, and then further cooled by RIEC. The LDD model, EC model and space model were established separately to facilitate the hybrid system simulation under the typical hot and humid condition in Hong Kong. The energy saving potential of the proposed system is quantitatively evaluated with respect to the conventional vapor compression A/C system. The results show an attractive energy saving ratio of 23.5% under Hong Kong weather condition. The energy saving ratio increases to 70% if the waste heat could be utilized.

Investigation on a Photovoltaic Thermoelectric Ventilator

Abstract A novel photovoltaic thermoelectric ventilator (PV-TEV) was proposed and investigated in this paper. In PV-TEV system, the outdoor fresh air is firstly heated up by PV airflow channel, and then heated up further when it flows through the hot side heat sink of thermoelectric ventilator into the indoor room. At the same time, the exhaust air cooled down the heat sink on the other side of the TEM when it is pumped out of the indoor environment. The electricity power of PV array is storage in battery, which can used to power the thermoelectric ventilator through voltage controller. The PV-TFAV system model was set up to calculate system performance with the actual solar radiation intensity and environment condition. The results show that the COPs and the fresh air temperature supplied for indoor is increased as the solar radiation intensify increase. The COPs are between 2.90 and 3.35 and the fresh air temperature is between 18.3 °C and 31 °C. This simply and environmentally friendly system is promising and worthwhile being applied to for low carbon buildings fresh air supply.

Controlled mechanical ventilation systems in residential buildings: Primary energy balances and financial issues

The aim of this paper is to investigate the technical, energy and financial convenience of Controlled Mechanical Ventilation (CMV) systems in residential units. With reference to a residential unit belonging to an apartment block, a mechanical ventilation system is first conceived according to different possible configurations (constant or hygro-adjustable flow, single or double flow). All the proposed configurations are suitable to provide fresh outdoor air and dilute indoor pollutants; this preliminary analysis allows to evaluate the overall costs for installation.Then, the paper determines the energy consumption for the operation of all the proposed configurations, both in terms of electricity to feed the blower fan and of fuel to preheat the cold air stream up to the indoor air temperature. Finally, these results are compared to the energy needs for a building without CMV systems, where air renewal is left to the occupants, who open and close windows at will. This analysis is proposed for three different sites in Italy, that show different climatic conditions.The results suggest that the adoption of controlled mechanical ventilation in residential units is a convenient practice under several points of view. Indeed, they undeniably allow to save primary energy, and the financial payback time is fairly low, particularly in cold climates.

Modeling and Simulation of Temperature Control System of Coating Plant Air Conditioner

The air conditioning system is an important external condition for coating production. Effectively controlling the air conditioning system temperature could ensure the external conditions required during the production process of the coating line, thus to ensure product quality. Due to the large temperature difference change rate of outdoor fresh air at some areas, the traditional PID control method can’t meet the temperature control requirements of the air conditioning system. In order to solve above problem, an actual plant air conditioning model was built based on the structure features of the truck coating plant air conditioning. An intelligent adaptive control algorithm was designed, then we performed matlab simulation on this model. Through the simulation, the experimental results show that the adaptive algorithm can meet the control requirements.

Investigation on the performance of a heat recovery ventilator in different climate regions in China

In recent years, haze becomes a choking problem in northern China in winter. A HRV (heat recovery ventilator) is an effective device to provide clean indoor environment by supplying fresh outdoor air to residential and commercial buildings, but the HRV system must be combined with an air filter to remove the fine particular matter of the outdoor air. There is limited information regarding this integrated system. This paper investigates the influences of an air filter on the performances of the HRV system in three modes by experiment and the application potential is also reported for this integrated system in five climate zones of China. The experimental results show that the integrated system can meet the required threshold value of 75 μg/m3, but the installation of an air filter reduces the air flow rate and increases the power of the fan. Compared to the HRV system, the sensible heat efficiencies of the integrated system are increased; and the total sensible heat transfer capacities are slightly decreased in the three modes. The case study shows that in Harbin and Beijing, the integrated system can recover more energy than that in other three cities in winter.

Optimal operation condition division with profit and losses analysis of energy recovery ventilator

Energy Recovery Ventilator (ERV) is one of the efficient ways to reduce fresh air load. However, there is a major concern, which energy recovery cannot trade off ERV's fan power consumption, even with causing counteraction to precool (preheat) fresh air in winter (summer). In this study, energy recovery is quantitatively evaluated during cooling season and heating seasons for an office building in Chongqing by employing TRNSYS. Based on the ERV's fan power consumption and energy saving which is converted to chiller's electricity consumption, outdoor fresh air is divided into four zones (zone I, zone II, zone III and zone IV) on a psychometric chart (ID chart). The results show that ERV which only operates in profit zones (zone III and zone IV) can increase electricity saving by 65.23% and reduce operating time by 31.18% than that operating throughout heating and cooling seasons. The proposed operation condition zones method can help identify profit pattern, minimize the energy consumption of ERV and air conditioning system.

Theoretical energy saving analysis of air conditioning system using heat pipe heat exchanger for Indian climatic zones

Heat pipe heat exchanger (HPHX) is an excellent device used for heat recovery in air conditioning systems. The Energy Conservation Building Code (ECBC) – Bureau of Energy Efficiency (BEE) India classifies Indian climatic zones into five categories viz., Hot and Dry (e.g. Ahmedabad, Jodhpur etc), Warm and Humid (e.g. Mumbai, Chennai etc), Composite (e.g. Nagpur, Jaipur etc), Cold (e.g. Guwahati etc) and Temperate (e.g. Bengaluru etc). The literature review indicated that very limited information is available on annual energy saving analysis of air conditioning system with HPHX for Indian climatic zones. The paper investigates the possible energy savings using HPHX for heat recovery in air conditioning system for Indian climatic zones. The analysis is carried out for total 25 Indian cities representing different climatic zones. The analysis is performed for a 6 row HPHX and assuming outdoor air quantity as 1 m3/s, return air dry bulb temperature as 23 °C and compressor power as 1 kW/TR. This paper discusses the use of HPHX only for the heat recovery application (exchange of sensible heat between fresh outdoor air and conditioned return air). The annual energy savings with HPHX for a particular city is calculated for number of hours when outdoor air dry bulb temperature exceeds 25 °C. The maximum energy saving potential is revealed for hot and dry, warm and humid and composite Indian climatic zones.

TRAJECTORY OF CONTAMINATED PARTICLE IN INTENSIVE CARE UNIT OF HOSPITALS USING NUMERICAL MODELING

Primary objective of air-conditioning is to create an indoor air quality and thermal condition of comfort suitable for persons / patients, with minimum energy cost. In air-conditioning system, ventilation airflow rate is the amount of fresh outdoor air introduced into the room to dilute CO2, contaminants and odours etc. Numerical model solves mass, momentum and energy equations. The contaminated particle (infection) which is simulated with a Lagrangian particle tracking model and the same has been carried out by simulation. This is usually a small part of the supply airflow rate which is introduced and distributed into the room at proper flow rate, velocity, temperature and relative humidity so as to remove the thermal loads and obtain conditions of thermal comfort. This is filtered to remove contaminants, mixed with ventilation air and conditioned by cooling / heating and humidifying / dehumidifying before introduction into the room. The study concerns about the health risk of the airborne diseases (bacteria, fungus, viruses etc.) from the patient to the other people in the ICU of hospital. By observing the movement of contaminated particle, it is advisable to keep the nurse- station and health care staff near the inlet to keep them healthy.

Experimental study on the heat recovery characteristic of a plate heat pipe heat exchanger in room ventilation

A plate heat pipe heat exchanger for use in a room ventilation system to cool or heat outdoor fresh air was designed in this study. One fresh air duct and one exhaust air duct were joined with the heat pipe heat exchanger to study the thermal performance of the thermal recovery system. A ratio of 1 for air volume flow rate between fresh and exhaust air was used to investigate the heat recovery effectiveness and the change in fresh air temperature. The fresh air temperature in the inlet duct was controlled in the range of 27 to 40°C under summer simulation conditions and in the range of 2 to 15°C under winter simulation conditions, whereas the temperature of exhaust air was controlled at approximately 24 and 18 C to simulate summer and winter conditions, respectively. The experimental results show that the temperature variations of fresh and exhaust air increase with increasing inlet fresh air temperature under summer conditions but decrease with increasing inlet temperature of fresh air under winter conditions. The maximum heat recovery effectiveness of the plate heat pipe heat exchanger was 58% in summer and 62% in winter. The change in effectiveness is moderate with different vacuum levels. At a vacuum of 1 × 10−3 Pa, the maximum effectiveness occurred when the filling ratio was 1:3. The experimental results showed that the heat pipe heat exchanger gained a high efficiency of heat recovery with low flow resistance. The energy conservation effect of this heat-pipe heat exchanger was evident.

Field testing of natural ventilation in college student dormitories (Beijing, China)

Human health demands and thermal comfort both require sufficient amounts of fresh outdoor air. Many university student dormitories in China have high residential density with no individual fresh air systems. In this kind of physical environment, natural ventilation is the primary way to obtain fresh outdoor air. However, few studies have explored ventilation under these conditions. In this paper, the ventilation rate in student dormitories (Beijing, China) was field-tested using carbon dioxide as a tracer gas. The test conditions were selected in accordance with the behavioral patterns of the occupants (students) throughout different seasons of the year. A stable CO2 release source was obtained from students in the sleep state. The results were used to create an empirical equation that could estimate the air change rate in a room. The CO2 concentration change in different dormitories was also discussed to evaluate the current ventilation and indoor air quality situation in the tested university student dormitories. Although sufficient outdoor air can be provided to dilute the indoor CO2 through single-sided natural ventilation in 82% of the testing period, nevertheless, for infiltration the indoor CO2 concentration exceeded the IAQ standard in 76% of the recorded times. The results were also factored into the design of student dormitories for better ventilation and indoor air quality.

Use of Indirect Evaporative Cooling as Pre-cooling Unit in Humid Tropical Climate: An Energy Saving Technique

Evaporative cooling system is an environmentally-friendly and energy saving technology for air conditioning. However, in hot and humid climates, it is rather inefficient due to the high wet bulb temperature of the ambient air. In order to take advantage of indirect evaporative cooling (IEC) system in humid tropical climates, we present a hybrid system that combines IEC system and vapor compression system. In the IEC unit, the exhaust air from the conditioned room is used as the working air, and outdoor fresh air is used as the product air so that the IEC unit produces pre-cooled air for vapor compression system. In this study, two types of IEC units, namely, a conventional counter flow IEC unit and a novel counter flow IEC unit based on M-cycle, have been numerically analyzed. Results have indicated that the humid outdoor fresh air can be pre-cooled to a temperature below its dew point temperature when the wet bulb temperature of the exhaust air is lower than the dew point temperature of the outdoor air. In addition, the use of IEC reduces the cooling load of the vapor compression system, as a result, the hybrid system has a large potential to reduce electricity demand and energy consumption.

Seasonal Weather Conditions Effect on Energy Consumption and CO2 Emission for Air Conditioning Systems Coupled with Enthalpy Energy Recovery Heat Exchanger

Seasonal energy consumption and subsequent CO2 gas emission analysis of an air conditioner coupled with paper based enthalpy energy recovery ventilator has been performed. Results were then compared with a conventional air conditioning system which mixes outdoor fresh air with room return air before cooling and resupplying. Effects of the enthalpy heat exchanger and air mixing system within the air conditioning system were modeled using a modified HPRate software code. Seasonal energy analysis for different weather conditions has shown that enthalpy energy recovery system is superior in the summer season. For a 300m2 office space, a seasonal saving of up to 1.4GJ in energy consumption and 900kg annual reduction of CO2 gas emission could be achieved provided that the membrane enthalpy heat exchanger is utilized instead of a conventional air mixing and conditioning system.

Developing a model for fibrous building materials

Ventilation systems are now used to ensure optimal indoor temperature and humidity in contemporary buildings such as showrooms, museums, offices, and homes. Winter indoor humidity can be very low due to the low humidity contained within fresh outdoor air supply. Humidification becomes necessary to raise indoor humidity, which also raises primary energy demand. Three approaches have been examined in a research project to reduce humidification/dehumidification energy consumption: (1) Moisture storage (absorption and emission of moisture-peaks) (2) Air flow control optimization (3) Moisture recovery by the ventilation system This paper focuses on the first approach, air humidification and dehumidification using moisture storage. A model was developed to illustrate both the microscopic and macroscopic hysteresis of moisture storage, and transport capacities of fibrous materials. The necessary parameters for the model have been obtained using measurements from a number of different materials that were used as humidity buffers. Precise equipment to measure humidity was constructed, tested, and used over a very long measurement period, during which detailed measurements of moisture absorption and emission were measured from different types of fibreboard sheets. The simulations generated by the model showed very good agreement with the measured results.

Thermal comfort and IAQ assessment of under-floor air distribution system integrated with personalized ventilation in hot and humid climate

The potential for improving occupants’ thermal comfort with personalized ventilation (PV) system combined with under-floor air distribution (UFAD) system was explored through human response study. The hypothesis was that cold draught at feet can be reduced when relatively warm air is supplied by UFAD system and uncomfortable sensation as “warm head” can be reduced by the PV system providing cool and fresh outdoor air at the facial level. A study with 30 human subjects was conducted in a Field Environmental Chamber. The chamber was served by two dedicated systems – a primary air handling unit (AHU) for 100% outdoor air that is supplied through the PV air terminal devices and a secondary AHU for 100% recirculated air that is supplied through UFAD outlets. Responses of the subjects to the PV-UFAD system were collected at various room air and PV air temperature combinations. The analyses of the results obtained reveal improved acceptability of perceived air quality and improved thermal sensation with PV-UFAD in comparison with the reference case of UFAD alone or mixing ventilation with ceiling supply diffuser. The local thermal sensation at the feet was also improved when warmer UFAD supply air temperature was adopted in the PV-UFAD system.

Sensitivity analysis of building energy use in different climates

Key design parameters (in terms of their influences on building energy consumption) through sensitivity analysis for fully air-conditioned office buildings in five cities (Harbin, Beijing, Shanghai, Kunming and Hong Kong) representing the five major climate zones (severe cold, cold, hot summer and cold winter, mild, and hot summer and warm winter) across China have been identified. These include: i) building envelope - window shading coefficient, window U-value and window-to-wall ratio; ii) internal load – equipment, lighting and occupancy; iii) HVAC system - outdoor fresh air, summer and winter thermostat set points, fan efficiency and fan static pressure; and iv) HVAC plant – chiller COP and boiler efficiency. The influence coefficient (IC, a ratio of the percentage change in computed output (building energy use) to the percentage change in input design parameter was used to indicate likely energy savings. For instance, Hong Kong has a lighting load IC of 0.359, suggesting that a 20% reduction (e.g. from 18 to 14.4 W/m 2 ) in lighting load could result in more than 7% reduction in the total building energy use. Furthermore, Hong Kong also has a summer thermostat set point IC of -1.131, suggesting that a 5% increase in the indoor temperature during the summer (e.g. from 26 to 27.3 o C) could result in about 6% energy savings. Given the growing awareness of adaptive thermal comfort, this could be a no-cost energy-efficient measure with great energy saving potential.