The simulated HVAC system consisting of an AHU for cooling the air of the personal ventilation modules and DV fan coil is dedicated to control the room air temeprature. The AHU controls the PV supply air temeprature while the flow rate can be regulated manually by the occupant. 

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... local body as described by Equation (7): Local Comfort 1⁄4 LogisticFunction ð S 1 þ offset Þ þ maxcomfort ð 7 Þ S1 represents local thermal sensation; the ‘‘offset’’ is the local sensation at which maximum comfort occurs; the ‘‘maxcomfort’’ indicates the maximum comfort level of local body, which may shifts to the left or right based on the whole body thermal state and would be higher than comfort level in neutral conditions when the local sensation is zero. The heat loss from the human body in conjunction with the DV-PV and the thermal space model are crucial factors for the determination of the thermal plumes around the human body and the ability of the jet flow to penetrate it. And since the local air conditioning is being considered here, the local thermal comfort is important and the human sensation is used to predict the eventual thermal draft and to assess the overall comfort associated with a certain jet flow. Also, the effect of the jet flow in bringing comfort to the upper human body segments can be predicted. Thus, the segmental and overall thermal comfort will serve as reference when comparing the energy consumptions of the DV system and the combined DV/PV system. The simulated building is an open office space located in the coastal area of Beirut. The climate is characterised to be Mediterranean with warm to hot summers and the weather data for a typical day of July were retrieved from the American University of Beirut (AUB) weather station records. The open-office has an 8 m  8 m square shape with a floor area of 64 m 2 and a ceiling height of 2.8 m. The external wall thickness is 0.17 m and is composed of 0.15 m heavyweight concrete and 0.02 m of expanded polystyrene. The internal walls are composed of 0.15 m heavyweight concrete without insulation. The walls are divided into north, south, west and east walls in addition to the ceiling and floor according to their orientation. The ceiling, floor, north wall and east wall are considered internal and adjacent to conditioned space while the south and west wall are external. The concrete properties are 2800 kg Á m À 3 for the density, 1000 J Á kg À 1 Á K À 1 for the specific heat capacity and 1.13 W Á m À 1 Á K À 1 for the thermal conductivity. Similarly for the expanded polystyrene: 950 kg Á m À 3 for the density, 1000 J Á kg À 1 Á K À 1 for the specific heat capacity and 0.05 W Á m À 1 Á K À 1 for the thermal conductivity. To account for the radiation effect, the emissivity and absorptivity of the walls material are used. The walls are considered as gray surfaces and the emissivity and absorptivity for long wave radiation are considered to be equal to 0.93 while the absorptivity for short wave radiation is equal to 0.7. The view factors of the different walls with respect to each other are also calculated. At full occupancy, 6 occupants dressed in typical office clothing of trousers and long-sleeved shirts would be present in the office and would contribute to both sensible and latent heat load. The insulation of this typical clothing ensemble is 0.61 clo [24]. The occupants would be considered exercising light office work and their metabolic rate according to ASHRAE Fundamentals would be 1.1 met for typing activity [24] (1 met 1⁄4 58.15 W Á m À 2 ). The human body heat losses can be computed and determined by the Bioheat thermal model according to the environmental conditions. The occupants’ presence in the room during 24 h would vary according to the profile in Figure 2. This occupancy behaviour profile was obtained from the European standard, EN15232 [25]. The fraction of full occupancy is defined as the ratio between the actual numbers of occupants to the maximum number of occupants that could be present in the office. The internal heat gain from office equipment is taken to be 6 W Á m À 2 which corresponds to the light load office of the ASHRAE Fundamentals [24]. The equipment heat gains would follow closely the occupancy schedule. In addition, a lighting load of 10 W Á m À 2 is considered. The main air-conditioning system for the office is a displacement ventilation system delivering air at a certain temperature and flow rate on the sidewall at the floor level while the return vent is located in the wall near the ceiling. The air is water cooled by a conventional chiller having a performance of 0.6 kW per ton. The aim of this system is to provide the cooling needed for the air outside the microclimate of the occupants. This could be achieved by controlling the flow rate of the supplied cold air at a certain temperature ranging between 18 8 C and 20 8 C according to the recommendations of the REHVA Guidebook [26]. While this DV system is in charge of the major part of the cooling load, it will supply 100% fresh air as in the conventional DV systems. On the other hand, the personal ventilation system will be installed and mounted on the office desks and directed towards the occupant’s upper body part according to the schematic shown in Figure 3. The PV modules can be controlled manually according to the occupant’s needs by modulating the flow rate at a certain fixed temperature (21–23 8 C) and allow conditioning of air in the vicinity of the human body known as the occupant’s microclimate. The system can deliver 100% fresh air at the human upper body and the breathing level to improve air quality. Individual fans having a nominal power consumption of 10 W to deliver a flow rate of up to 10 L Á s À 1 . The air-conditioning system of the office can be operated by a standalone DV system delivering air at a constant temperature with a variable flow rate. When operating the PV modules, the temperature of the DV is maintained constant while its flow rate can be varied automatically and the PV flow rate can vary according to the occupant’s needs. The DV and PV systems are operated simultaneously to keep the occupant in an acceptable comfort level. The internal temperature of the office will be controlled through a fixed set point temperature. In order to study more accurately the occupants’ thermal comfort this set point temperature is based on the operative temperature of the space (referred to as ‘‘temperature’’ in the rest of the paper). Because of the vertical temperature gradient characterising the DV systems, the set point temperature is measured at a height of 1 m from the floor away from the human body. The DV system would be in charge of maintaining this set room temperature by a variable supply flow rate. The system would turn on during potential occupancy hours (5:00–24:00) and the flow rate would vary according to the deviation of the room actual temperature from the set point temperature. While maintaining the ambient air temperature at the reference set point, the PV modules air flow rate would vary to maintain a neutral thermal sensation and an acceptable comfort level in the occupants’ microclimates. The microclimate zone is considered to be formed of layers adjacent to the upper body part of the occupant, i.e. the occupant’s microclimate parameters including the terminal PV air temperature and velocity are obtained by taking their respective mean values in this zone. The maximum air flow rate supplied by the PV modules is 10 L Á s À 1 per occupant ( $ 20 CFM per occupant) according to the ventilation recommendations of ASHRAE Standard 62.1– 2009 [27]. The total amount of fresh air supplied would vary according to the occupancy level and the number of occupants present in the office at a time. As stated previously, the DV system is in charge of reaching the desired room temperature by varying its flow rate at a given supply temperature which was chosen to be 20 8 C. However, the PV modules flow rates are under the control of the occupants while their supplied air temperature is preset. The energy need of personalised ventilation system compared to a conventional displacement ventilation system was studied for three different parameters of the supply personalised ventilation air temperature. The energy saving potential of these parameters is also studied. In total, 9 simulation cases including 3 personalised air supply temperature strategies: 20 8 C, 21 8 C and 22 8 C, and three allowed air temperatures: 26 8 C, 27 8 C and 28 8 C were simulated. In addition, the personalised air supply flow rate was variable and regulated to maintain a neutral thermal sensation of the human body. The PV flow rate was bounded by a minimum of 0 L Á s À 1 and a maximum of 10 L Á s À 1 . The simulated cases are summarised in Table 1. In order to identify each simulation case apart, an identification code of two parts was defined and labelled. The personalised air temperature was identified using the notation t20, t21 or t22. Similarly, the maximum allowed room air temperature was identified using the notation r26, r27 and r28. For example the case t21–r27 would means that personalised air temperature of 21 8 C would be supplied to a room with a maximum allowed room air temperature of 27 8 C. To compare the results and evaluate the energy saving potential, a reference case was simulated. In this reference case, the displacement ventilation system was operating alone and supplying the necessary amount of air according to the occupancy. The supply air flow rate was regulated automatically to keep the temperature of the space around 24 8 C. To evaluate the energy need of the office, the electrical energy consumption of the various components was estimated: i.e. E cooling , the electrical energy consumption of the chiller and E fans , the electrical energy consumption of the individually controlled PV fans. In the system considered, the occupants do not have control over the PV air supply temperature. This temperature is meant to be set automatically or by the manager of the building according to the external or the internal air temperature. In order to test how this set temperature could affect the energy savings of the system and the comfort of the ...