Performance evaluation and life cycle cost analysis of earth to air heat exchanger integrated with adobe building for New Delhi composite climate

This paper aims to develop thermal model of a vault roof building integrated with earth to air heat exchanger (EAHE). The building under consideration is made of brick vault and adobe (or mud) structures. The methodology adopted for developing thermal model of this building with six interconnected rooms is presented in this paper. The energy balance equations were solved simultaneously using fourth order Runge-Kutta numerical technique. The results from the thermal model were validated using experimental observed data. Experimental results showed that the room air temperature during winter was found 5-15 °C higher as compared to ambient air temperature while lower during summer months. The results show that annual energy saving potential of the building before and after integration of EAHE were 4946 kWh/year and 10321 kWh/year respectively. The seasonal energy efficiency ratio (SEER) for EAHE was determined as 2-3. This considerable increase in annual energy savings potential of building due to EAHE leads to mitigation of CO₂ emissions about 16 tons/year and the corresponding annual carbon credit of building was estimated as € 340/year. The life cycle cost (LCC) analysis shows that the payback period is less than 2 years for the investment on EAHE system.     

Determining the optimal design of a closed loop earth to air heat exchanger for greenhouse heating by using exergoeconomics

This investigation deals with an exergoeconomic evaluation of the earth to air heat exchanger (EAHE) application for determining the optimal design greenhouse heating in Izmir, Turkey. The exergy destructions in the system are quantified and illustrated using tables for a reference temperature of 6 °C. The results indicate that the exergy destructions in the system occur primarily as a result of blower losses and heat exchanger losses. These average losses account for 85% and 4.5%, respectively. Both COP and exergy efficiency of the overall system was investigated to analyze and improve the systems performance. The average COP and exergetic efficiency were determined to be 10.51 and 89.25%, respectively. The results may provide useful insights into the relations between thermodynamics and economics for the EAHE heating systems.     

Performance evaluation of a hybrid photovoltaic thermal double pass facade for space heating

This paper presents the performance evaluation of a hybrid photovoltaic thermal (Semi transparent PVT) double pass facade for space heating. The thermal model has been developed by using the energy balance equations of the proposed hybrid photovoltaic thermal double pass facade under quasi-steady state condition. Numerical computations have been carried out for the composite climate of New Delhi, India. An analysis has been carried out to calculate annual energy and exergy gain for the hybrid photovoltaic thermal double pass facade. On the basis of numerical results it has been observed that the annual thermal and electrical energy are 480.81 kWh and 469.87 kWh respectively. The yearly overall thermal energy generated by the system has been calculated as 1729.84 kWh. It is also observed that the room air temperature increases by 5-6 °C than the ambient air temperature for a typical winter day.     

A heat pipe photovoltaic/thermal (PV/T) hybrid system and its performance evaluation

Building-integrated photovoltaic/thermal (BIPV/T) system has been considered as an attractive technology for building integration. The main part of a BIPV/T system is PV/T collector. In order to solve the non-uniform cooling of solar PV cells and control the operating temperature of solar PV cells conveniently, a heat pipe photovoltaic/thermal (PV/T) hybrid system (collector) has been proposed and described by selecting a wick heat pipe to absorb isothermally the excessive heat from solar PV cells. A theoretical model in terms of heat transfer process analysis in PV module panel and introducing the effectiveness-number of transfer unit (?-NTU) method in heat exchanger design was developed to predict the overall thermal-electrical conversion performances of the heat pipe PV/T system. A detailed parametric investigation by varying relevant parameters, i.e., inlet water temperature, water mass flow rate, packing factor of solar cell and heat loss coefficient has been carried out on the basis of the first and second laws of thermodynamics. Results show that the overall thermal, electrical and exergy efficiencies of the heat pipe PV/T hybrid system corresponding to 63.65%, 8.45% and 10.26%, respectively can be achieved under the operating conditions presented in this paper. The varying range of operating temperature for solar cell on the absorber plate is less than 2.5 °C. The heat pipe PV/T hybrid system is viable and exhibits the potential and competitiveness over the other conventional BIPV/T systems.     

Modeling and comparative thermal performance of ground air collector and earth air heat exchanger for heating of greenhouse

The potential of using the stored thermal energy of ground for space heating has been investigated with the help of two buried pipe systems, i.e., ground air collector and earth air heat exchanger, integrated with the greenhouse located in the premises of Indian Institute of Technology, Delhi, India. The total length of the buried pipes in both the arrangements was kept same for making a comparative study. A complete numerical model has been developed to predict and compare their thermal performance for choosing a suitable heating method in the composite climate of India. Experiments were conducted extensively during winter period from November 2002 to March 2003, but the model was validated against the clear and sunny days. Performance of these two arrangements was compared in terms of thermal load leveling and total heating potential. Temperatures of greenhouse air with ground air collector were observed to be 2–3 °C higher than those with earth air heat exchanger. The temperature fluctuations of greenhouse air were also less when operated with ground air collector as compared to earth air heat exchanger. Predicted and computed values of greenhouse air temperatures in both the systems exhibited fair agreement. Finally ground air collector was chosen as a suitable option for heating of greenhouse in the above climate.     

Condenser heat recovery with a PV/T air heating collector to regenerate desiccant for reducing energy use of an air conditioning room

This paper presents an experimental test along with procedures to investigate the validity of a developed simulation model in predicting the dynamic performance of a condenser heat recovery with a photovoltaic/thermal (PV/T) air heating collector to regenerate desiccant for reducing energy use of an air conditioning room under the prevailing meteorological conditions in tropical climates. The system consists of five main parts; namely, living space, desiccant dehumidification and regeneration unit, air conditioning system, PV/T collector, and air mixing unit. The comparisons between the experimental results and the simulated results using the same meteorological data of the experiment show that the prediction results simulated by the model agree satisfactorily with those observed from the experiments. The thermal energy generated by the system can produce warm dry air as high as 53 °C and 23% relative humidity. Additionally, electricity of about 6% of the daily total solar radiation can be obtained from the PV/T collector in the system. Moreover, the use of a hybrid PV/T air heater, incorporated with the heat recovered from the condenser to regenerate the desiccant for dehumidification, can save the energy use of the air conditioning system by approximately 18%.     

The cooling potential of earth–air heat exchangers for domestic buildings in a desert climate

A theoretical model of an earth–air heat exchanger (EAHE) is developed for predicting the outlet air temperature and cooling potential of these devices in a hot, arid climate. The model is validated against other published models and shows good agreement. A sub-soil temperature model adapted for the specific conditions in Kuwait is presented and its output compared with measurements in two locations. A building model representative of a typical Kuwaiti dwelling has been implemented and all the models have been encoded within the TRNSYS-IISIBAT environment. A typical meteorological year for Kuwait was prepared and used to predict the cooling loads of the air-conditioned dwelling with and without the assistance of the EAHE. Simulation results showed that the EAHE could provide a reduction of 1700 W in the peak cooling load, with an indoor temperature reduction of 2.8 °C during summer peak hours (middle of July). The EAHE is shown to have the potential for reducing cooling energy demand in a typical house by 30% over the peak summer season.     

Modeling of energy performance of a house with three configurations of building-integrated photovoltaic/thermal systems

A theoretical and experimental study of energy performance of three different open loop air heating building-integrated photovoltaic/thermal (BIPV/T) systems that utilize recovered heat for home heating is presented. The configurations are: Configuration 1: base case of unglazed BIPV with airflow under it; Configuration 2: addition of 1.5 m vertical glazed solar air collector in series with Configuration 1; Configuration 3: addition of a glazing over the PV. The model developed has been verified against experimental data from a solar research house for Configuration 1. Obtained relationships for BIPV/T system exiting air temperature as function of solar irradiance and air speed in PV cavity may be used for developing fan airflow control strategies to achieve desired outlet air temperature suitable for different applications. For Configuration 1, preheated air is suitable for HVAC system and domestic hot water (DHW) preheating. Higher outlet air temperatures of the PV cavity suitable for DHW might be achieved by utilizing Configurations 2 or 3. With Configuration 2, significant outlet air temperatures are achieved in winter along with enhanced thermal efficiency making it suitable for coupling with a rockbed heat storage. Finally, Configuration 3 significantly reduces electricity production and may lead to excessively high PV panel temperatures.     

Energy and exergy analysis of photovoltaic/thermal integrated with a solar greenhouse

In this paper, an attempt has been made to validate the thermal model with experimental results of a typical day August, 25, 2006 for clear weather condition of New Delhi. An energy and exergy analysis for the prediction of performance of a photovoltaic/thermal (PV/T) collector integrated with a greenhouse at I.I.T, Delhi, India has been carried out. The analysis is based on quasi-steady state condition. Experiments have been conducted extensively during period from June 2006 to May 2007, for annual performance. Numerical computation has been carried out for a typical day only for validation. It is observed that the theoretical value of solar cell, tedlar back surface and greenhouse room air temperatures is approximately equivalent to the experimental values. The predicted and measured values of solar cell, tedlar back surface and greenhouse air temperatures have been verified in terms of root mean square of percent deviation (7.05–17.58%) as well as correlation coefficient (0.95–0.97) and both exhibit fair agreement. Exergy analysis calculations of the PV/T integrated greenhouse system show an exergy efficiency level of approximately 4%.     

Thermal modeling of a greenhouse with an integrated earth to air heat exchanger: an experimental validation

A simplified analytical model is developed to study the year round effectiveness of a recirculation type earth air heat exchanger coupled with a greenhouse located in IIT Delhi, India. The performance of the system was evaluated in terms of thermal load leveling and coefficient of performance. Calculations were done for typical winter and summer day in year 2002. Temperatures of greenhouse air were found to be on an average 6–7 °C more in winter and 3–4 °C less in summer than the same greenhouse when operating without earth air heat exchanger. Predicted and measured values of greenhouse air temperatures exhibited fair agreement.     

Power consumption benchmark for a semiconductor cleanroom facility system

Benchmarking is an important step in implementing energy conservation in a semiconductor fabrication plant (hereafter referred to as “fab”). A semiconductor cleanroom facility system is complicated, usually comprised of several sub-systems, such as a chilled water system, a make-up system, an exhaust air system, a compressed air system, a process cooling water (PCW) system, a nitrogen system, a vacuum system, and an ultra-pure water (UPW) system. It is a daunting task to allocate energy consumption and determine an optimum benchmark. This study aims to establish the energy benchmark of a typical 8-in. DRAM semiconductor fab through field measurement data. Results of the measured energy consumption index were: chilled water system (including chiller, chilled water pump and cooling tower): 0.257 kW/kW (=0.9 kW/RT) in summer and 0.245 kW/kW (=0.86 kW/RT) in winter air recirculation air system: 0.00018 kWh/m³ make-up air system: 0.0042 kWh/m³ general exhaust air system: 0.0007 kWh/m³ solvent exhaust air system: 0.0021 kWh/m³ acid exhaust air system: 0.0009 kWh/m³ alkaline exhaust air system: 0.0025 kWh/m³ nitrogen system: 0.2209 kWh/m³ compressed dry air system: 0.2250 kWh/m³ process cooling water system: 1.3535 kWh/m³ and ultra-pure water system: 9.5502 kWh/m³. These data can be used to assess the efficiency of different energy-saving schemes and as a good reference for factory authorities. The PCW system's status before and after implementing energy conservation is discussed.     

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/m² a was recorded for the TABS case; in contrast, the conventional all-air (VAV) equipped building incurs a primary energy intensity of 229 kWh/m²a, 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.     

Thermal modeling for greenhouse heating by using thermal curtain and an earth–air heat exchanger

In this paper, a thermal model for heating of greenhouse by using different combinations of inner thermal curtain, an earth–air heat exchanger, and geothermal heating has been developed. The analysis incorporates the study of thermal performance of three-zone greenhouse. The calculations have been made for a typical production greenhouse in southern part of Argentina; available climatic data has been used. The thermal performance of a greenhouse having thermal curtain and an earth–air heat exchanger has been compared with a greenhouse having thermal curtain and geothermal energy. It is seen that the fluctuations in temperature in the vicinity of plants are comparable in the two cases. From the results, it is seen that an earth–air heat exchanger might prove an alternative source for heating of greenhouse when geothermal energy is not available. It has also been observed that, the increase in temperature of zone I is more for the greenhouse with geothermal than the greenhouse with an earth–air heat exchanger.     

Exergetic performance assessment of a solar photovoltaic thermal (PV/T) air collector

In this paper, an attempt is made to evaluate the exergetic performance of a solar photovoltaic thermal (PV/T) air collector. A detailed energy and exergy analysis is carried out to calculate the thermal and electrical parameters, exergy components and exergy efficiency of a typical PV/T air collector. Some corrections are done on related heat loss coefficients. An improved electrical model is used to estimate the electrical parameters of a PV/T air collector. Further, a modified equation for the exergy efficiency of a PV/T air collector is derived in terms of design and climatic parameters. A computer simulation program is also developed to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Finally, parametric studies have been carried out. It is observed that the modified exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature. It is also found that the thermal efficiency, electrical efficiency, overall energy efficiency and exergy efficiency of PV/T air collector is about 17.18%, 10.01%, 45% and 10.75% respectively for a sample climatic, operating and design parameters.     

1st Environmental conference of Thessaly region, 8–10 September 2012, Hotel Skiathos Palace,Koukounaries, Skiathos Island,Greece

This study was conducted with the aim to assess the potential performance of a photovoltaic thermal mechanical ventilation heat recovery (PV/T MVHR) system. The device is currently considered for the application to the Z-en house project undertaken by Scottish homebuilder. The house’s whole energy demand was calibrated based on the UK Government’s standard assessment procedure for energy rating of dwellings, while the PV/T performance was estimated using an ‘EESLISM’ energy and environmental design simulation tool developed by Kogakuin University. This study concluded that PV generates heat, which makes the fresh air running under the PV roof 10–15?°C warmer than the outside temperature even during the Scottish winter and this warm air extracted from roof-integrated PV modules can be used to help reduce the domestic space-heating demand. Thus, the building-integrated PV/T MVHR system was considered as one of the effective means to assist the net zero energy operation of housing in cool and cold climates, whose dominant domestic energy comsumption derives from space heating.     

Energy partition and conversion of solar and thermal radiation into sensible and latent heat in a greenhouse under arid conditions

For a greenhouse thermal analysis, it is essential to know the energy partition and the amount of solar and thermal radiation converted into sensible and latent heat in the greenhouse. Factors that are frequently needed are: efficiency of utilization of incident solar radiation (π), and sensible and latent heat factors (η and δ). Previous studies considered these factors as constant parameters. However, they depend on the environmental conditions inside and outside the greenhouse, plants and soil characteristics, and structure, orientation and location of the greenhouse. Moreover, these factors have not yet been evaluated under the arid climatic conditions of the Arabian Peninsula.In this study, simple energy balance equations were applied to investigate π, η and δ; energy partitioning among the greenhouse components; and conversion of solar and thermal radiation into sensible and latent heat. For this study, we used an evaporatively cooled, planted greenhouse with a floor area of 48 m². The parameters required for the analysis were measured on a sunny, hot summer day. The results showed that value of π was almost constant (≅0.75); whereas the values of η and δ strongly depended on the net radiation over the canopy (R_na); and could be represented by exponential decay functions of R_na.At a plant density corresponding to a leaf area index (LAI) of 3 and an integrated incident solar energy of 27.7 MJ m⁻² d⁻¹, the solar and thermal radiation utilized by the greenhouse components were 20.7 MJ m⁻² d⁻¹ and 3.74 MJ m⁻² d⁻¹, respectively. About 71% of the utilized radiation was converted to sensible heat and 29% was converted to latent heat absorbed by the inside air. Contributions of the floor, cover and plant surfaces on the sensible heat of the inside air were 38.6%, 48.2% and 13.2%, respectively.     

Thermal behavior of a novel type see-through glazing system with integrated PV cells

Steady natural convective airflow in a novel type glazing system with integrated semi-transparent photovoltaic (PV) cells has been analyzed numerically using a stream function vorticity formulation. Based on the resulting numerical predictions, the effects of Rayleigh numbers on airflow patterns and local heat transfer coefficients on vertical glazing surfaces were investigated for Rayleigh numbers in the range of 10³ ≤ Ra ≤ 2 × 10⁵. Significant agreement for the Nusselt numbers was observed between numerical simulation results in this study and those of earlier experimental and theoretical results available from the literature. In addition, the effect of air gap thickness in the cavity on the heat transfer through the cavity is evaluated. The optimum thickness of the air layer in this research is found to be in the range of 60–80 mm. This novel glazing system type could not only generate electricity but also achieve potential energy savings by reducing the air conditioning cooling load when applied in subtropical climatic conditions and simultaneously provide visual comfort in the indoor environment.     

Performance analysis of earth-pipe-air heat exchanger for summer cooling

Earth-pipe-air heat exchanger (EPAHE) systems can be used to reduce the cooling load of buildings in summer. A transient and implicit model based on computational fluid dynamics was developed to predict the thermal performance and cooling capacity of earth-air-pipe heat exchanger systems. The model was developed inside the FLUENT simulation program. The model developed is validated against experimental investigations on an experimental set-up in Ajmer (Western India). Good agreement between simulated results and experimental data is obtained. Effects of the operating parameters (i.e. the pipe material, air velocity) on the thermal performance of earth-air-pipe heat exchanger systems are studied. The 23.42 m long EPAHE system discussed in this paper gives cooling in the range of 8.0-12.7 °C for the flow velocities 2-5 m/s. Investigations on steel and PVC pipes have shown that the performance of the EPAHE system is not significantly affected by the material of the buried pipe (pipe). Velocity of air through the pipe is found to greatly affect the performance of EPAHE system. The COP of the EPAHE system discussed in this paper varies from 1.9 to 2.9 for increase in velocity from 2.0 to 5.0 m/s.     

Performance analysis of earth-pipe-air heat exchanger for winter heating

Earth-pipe-air heat exchanger (EPAHE) systems can be used to reduce the heating load of buildings in winter. A transient and implicit model based on computational fluid dynamics is developed to predict the thermal performance and heating capacity of earth-air-pipe heat exchanger systems. The model is developed inside the FLUENT simulation program. The model developed is validated against experimental investigations on an experimental set-up in Ajmer (Western India). Good agreement between simulated results and experimental data is obtained. Effects of the operating parameters (i.e. the pipe material, air velocity) on the thermal performance of earth-air-pipe heat exchanger systems are studied. The 23.42 m long EPAHE system discussed in this paper gives heating in the range of 4.1-4.8 °C for the flow velocities 2-5 m/s. Investigations on steel and PVC pipes have shown that performance of the EPAHE system is not significantly affected by the material of the buried pipe. Velocity of air through the pipe is found to greatly affect the performance of EPAHE system.     

Real climate experimental study of two double window systems with preheating of ventilation air

This paper aims to characterize the thermal performance of a window system that consists in doubling an existing window, converting it into a ventilated double window. The air coming from the outside circulates upwards through the channel between windows and enters the building through a vent on the top of the window's case. A series of experimental measurements was conducted in a test cell exposed to real outdoor weather conditions located in a mountain region at Centre of Portugal, during heating season in order to determine how this window system can act as a heat exchanger. It was found that such window system act as an efficient heat exchanger using transmission heat losses and solar radiation to preheat ventilation air, thus reducing the building's operational energy costs. An average of about 19 m³/h of air flow rate was found with an air temperature increment within the air gap of about 6 °C, during night-time, for an indoor/outdoor temperature difference of about 16 °C. Air temperature increment reached up to 12 °C using a plastic shutter. With solar radiation, the average of that increment was about 10 °C. This is a simple and cheap building technology which can be implemented both in new and existing buildings.