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Jan 8, 2016 - In general, the dynamic system provided the best comfort conditions, even if it involves a worse ... Keywords: dynamic system; ventilation; heat recovery; co-heating; thermal .... Heating and cooling periods and weather data.
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Assessment of the Performance of a Ventilated Window Coupled with a Heat Recovery Unit through the Co-Heating Test Ludovico Danza *,† , Benedetta Barozzi † , Lorenzo Belussi † , Italo Meroni † and Francesco Salamone † Received: 10 November 2015; Accepted: 5 January 2016; Published: 8 January 2016 Academic Editor: Mat Santamouris Construction Technologies Institute of National Research Council of Italy, Via Lombardia 49, San Giuliano Milanese, Milano 20098, Italy; [email protected] (B.B.); [email protected] (L.B.); [email protected] (I.M.); [email protected] (F.S.) * Correspondence: [email protected]; Tel.: +39-02-9806-424; Fax: +39-02-9828-0088 † These authors contributed equally to this work.

Abstract: The aim of the article is to describe the results of an experimental campaign based on the assessment of a heat recovery unit coupled with a dynamic window. Two fully monitored and calibrated outdoor test cells are used, in order to evaluate the energy performance and the related thermal comfort. The former presents a traditional window with double-glazing, aluminum frame and indoor blind and a centrifugal extractor for the air circulation. The latter is equipped with a dynamic window with ventilated and blinded double-glazing provided with a heat exchanger. The connection of the dynamic window and heat recovery unit provides different actions: heat recovery; heat transfer reduction; pre-heating before the exchanger. Different operating configurations allowed the trends of the dynamic system to be assessed in different seasons in terms of energy saving, thermal comfort behavior and energy efficiency. The results showed an overall lower consumption of the innovative system, both in winter and summer, with 20% and 15% energy saving, respectively. In general, the dynamic system provided the best comfort conditions, even if it involves a worse behavior than expected, in the summer season. Keywords: dynamic system; ventilation; heat recovery; co-heating; thermal comfort; energy efficiency

1. Introduction As consequence of the Energy Performance of Buildings Directive (EPBD) recast 2010/31/CE, more restricted requirements for energy saving in existing and new buildings have been imposed. New buildings have a limited impact on overall energy saving as they represent just a fraction of the whole building stock [1]. The existing buildings constitute, therefore, the greatest opportunity for energy efficiency improvements [2], even if the refurbishment process is still slow [3]. At the global scale, the energy consumption of buildings represents about the 40% of the overall consumption [4] with the largest share due to the residential buildings in European countries and quite equally divided between domestic and commercial buildings in the USA [5]. The improvement of the energy efficiency of the building stock is an important step in minimizing the environmental impact of modern society. In particular, an important role is played by the tertiary buildings, thanks to a major attitude toward changes related to a wide economic vision [6]. In this category, the office buildings are those with highest consumption and CO2 emissions [7]; they represent a starting point to achieve energy improvement.

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The achievement of nearly zero energy balance of existing office buildings should be pursued, first of all, by reducing the energy losses and maximizing energy saving. This can be achieved through suitable architectural and constructive choices in order to control the energy fluxes induced by weather conditions and building operations. A performant building envelope allows the energy consumption to be reduced [8]. Different actions may be fielded to achieve this purpose and, among them, the interventions on the glazing systems play a key role [9]. The potential benefits of glazing systems on energy balance are still debated, above all from the near-zero energy buildings perspective [10,11]. The glazing systems should be designed as components that gain more energy than they lose in winter and just the opposite in summer in order to positively contribute to the energy balance of a building. Moreover, the glazing system should reduce the losses by infiltration and exfiltration, ensuring a reasonable air change, thanks to an efficient heat recovery unit [12]. Starting from this assumption, different transparent components have been developed, including the ventilated glazing systems. In a previous work, the authors demonstrated the variability of the thermal transmittance of a prototypal ventilated window equipped with a suction fan to generate an airflow in the gap between the glazing and an internal blind [13]. The total heat transfer of the ventilated window is directly proportional and inversely proportional with the flow rate increase in summer and in winter, respectively. The article describes the results of an experimental campaign carried out on a dynamic window consisting of a ventilated window coupled with a heat recovery unit installed on an external test cell, following the guidelines of the co-heating test method [14]. The authors intend to test the performance of the coupled system, with respect to a traditional window installed in a similar test cell where the same airflow rate is assured by a forced air change. Other physical implications on the use of the ventilated window are not analyzed in this article but they will be the topics of other studies considering the installation in real buildings. The performance was analyzed in terms of energy saving achieved by the system and indoor thermal comfort. The former is assessed in terms of cumulated consumption and the Energy Signature method [15] has been applied, aimed at assessing the overall energy behavior in different climatic conditions. For the latter purpose, the psychrometric analysis is applied to better understand the complex heat fluxes management [16]. 2. Experimental Section The experimental campaign, carried out on dedicated outdoor test cells located at the ITC-CNR headquarters in San Giuliano Milanese near Milan, involved two phases: the former aimed at analyzing the energy saving due to the installation of the dynamic system, the latter aimed at assessing the indoor thermo-hygrometric comfort. 2.1. Description of the Test Cells The test cells, called C2 and C3, respectively, have the same geometric, constructive and thermo-physical characteristics. Their dimensions are 2.80 m ˆ 2.80 m ˆ 5 m and they are realized in lightweight concrete blocks with external insulation. The thermal transmittance of walls, floor and ceiling are equal to 0.20, 0.20 and 0.31 W/m2 K, respectively. The thermal capacity of each cell is equal to 2261 kJ/K. Both cells are equipped with a thermostat aimed at maintaining a constant indoor air temperature equal to 20 ˝ C for the entire experiment. Both cells are also equipped with a ceiling fan to ensure the homogenization of the internal air temperature and to prevent vertical temperature stratification. The cells are completely monitored with temperature and relative humidity indoor sensors and with an electrical energy meter (Figure 1).

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    Figure 1. Section of the test cell and position of the internal sensors.    Figure 1. Section of the test cell and position of the internal sensors.   Figure 1. Section of the test cell and position of the internal sensors. 

In  C2,  a  traditional  window  with  a  south‐exposed  low  emission  double‐glazing  (3.3‐16‐3),  In  C2, C2,  aa  traditional traditional  window window  with with  aa  south-exposed south‐exposed  low low  emission emission  double‐glazing  (3.3-16-3), (3.3‐16‐3),  2K) and micro‐drilled blind were  In double-glazing aluminum frame (overall thermal transmittance equal to 1.7 W/m 2K) and micro‐drilled blind were  2 aluminum frame (overall thermal transmittance equal to 1.7 W/m aluminum frame (overall thermal transmittance equal to 1.7 W/m K) and micro-drilled blind were installed with a centrifugal extractor for the air circulation placed on the north wall, on the opposite  installed with a centrifugal extractor for the air circulation placed on the north wall, on the opposite  installed with a centrifugal extractor for the air circulation placed on the north wall, on the opposite side of the window, as shown in Figure 3a. The C3 was equipped with a south‐exposed dynamic  side of the window, as shown in Figure 3a. The C3 was equipped with a south‐exposed dynamic  side of the window, as shown in Figure 3a. The C3 was equipped with a south-exposed dynamic system system made with a double‐glazing window and internal blind with the same characteristics of C2,  system made with a double‐glazing window and internal blind with the same characteristics of C2,  made withthe  a double-glazing and internal blind with same of C2,to  in a  which in  which  ventilated  air  window gap,  between  the  glass  and  the the blind,  is characteristics directly  connected  heat  in  which  the  ventilated  air  gap,  between  the  glass  and  the  blind,  is  directly  connected  to  a  heat  heat  the ventilated air gap, and the blind, is directly connected to a heatof  exchanger exchanger  (Figure  1b), between ensuring the the glass required  airflow  rate.  The  nominal  performance  the  exchanger  (Figure  1b),  ensuring  the  required  airflow  rate.  The  nominal  performance  of  the  heat  (Figure 1b), ensuring the required airflow rate. The nominal performance of the heat recovery unit is recovery unit is about 90%. The average ventilation losses represent about 28% of the total of the test  recovery unit is about 90%. The average ventilation losses represent about 28% of the total of the test  about 90%. The average ventilation losses represent about 28% of the total of the test cells. In both cells. In both the cells, the air conditioning system consisted of an electric heater and a heat pump,  cells. In both the cells, the air conditioning system consisted of an electric heater and a heat pump,  the cells, the air conditioning system consisted of an electric heater and a heat pump, for winter and for winter and summer, respectively. The internal gains are negligible.  for winter and summer, respectively. The internal gains are negligible.  summer, respectively. The internal gains are negligible. In the first prototype of the dynamic window, the ventilation was ensured by a fan located in  In the first prototype of the dynamic window, the ventilation was ensured by a fan located in  In the of the dynamic the ventilation was ensured by athe  fanblind  located in the  the the  top  of first the  prototype window  frame,  drawing window, air  through  the  gap  placed  between  and  the of top  the  window  drawing  air  through  gap  placed  the between  the  blind  and  the  top theof  window frame,frame,  drawing air through the gap the  placed between blind and the innermost innermost glass sheet [13]. The air suction created a vacuum in the cavity, thus triggering convective  innermost glass sheet [13]. The air suction created a vacuum in the cavity, thus triggering convective  glass sheet [13]. Thethe  airroom.  suction created vacuum in the cavity, thus triggering circulation circulation  within  The  inlet aair  was  then  expelled  to  the  outdoor convective environment  both  in  circulation  within  the  room.  The  inlet  air  was  then  expelled  to  the  outdoor  environment  both  in  within the room. The inlet air was then expelled to the outdoor environment both in summer and summer and in winter. The goal is to remove the heat accumulated behind the glass and reduce the  summer and in winter. The goal is to remove the heat accumulated behind the glass and reduce the  in winter.transmittance.  The goal is toThe  remove the heat accumulated behind the glass reducedetecting  the thermal thermal  operation  of  the  system  was  controlled  by and sensors,  the  thermal  transmittance.  The  operation  of  the  system  was  controlled  by  sensors,  detecting  the  transmittance. The operation of the  the system was controlled by remotely  sensors, detecting thethe  temperature ofand  the temperature  of  the  glass  and  environment.  A  device  controlled  fan  speed  temperature  of  the  glass  and  the  environment.  A  device  remotely  controlled  the  fan  speed  and  glass and the environment. A device remotely controlled the fan speed and adjusted its ignition time. adjusted its ignition time.  adjusted its ignition time.  In In  the the  current current  experimental experimental  campaign, campaign,  the the  dynamic dynamic  system system  is is  built built  without without  active active  integrated integrated  In  the  current  experimental  campaign,  the  dynamic  system  is  built  without  systems, such as the fan, and the above section of the gap is directly connected toactive  a heatintegrated  recovery systems, such as the fan, and the above section of the gap is directly connected to a heat recovery unit  systems, such as the fan, and the above section of the gap is directly connected to a heat recovery unit  unit to exploit preheating of the through the system(Figure  (Figure2).  2).The  Thestructure  structure of  of the  the heat so  as soto asexploit  the the preheating  of  the  air air through  the  system  heat  so  as  to  exploit  the  preheating  of  the  air  through  the  system  (Figure  2).  The  structure  of  the  heat  exchanger is made of foamed polypropylene; it is equipped with a bypass system that turns off the exchanger is made of foamed polypropylene; it is equipped with a bypass system that turns off the  exchanger is made of foamed polypropylene; it is equipped with a bypass system that turns off the  recovery in specific environmental conditions defined by the manufacturer. recovery in specific environmental conditions defined by the manufacturer.  recovery in specific environmental conditions defined by the manufacturer. 

   

Figure 2. (a) Outside view of the test cells: C2 on the right side, C3 on the left side; (b) Internal view  Figure 2. (a) Outside view of the test cells: C2 on the right side, C3 on the left side; (b) Internal view Figure 2. (a) Outside view of the test cells: C2 on the right side, C3 on the left side; (b) Internal view  of C3.  of C3. of C3. 

   

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The indoor air is forced to pass through the air gap due to the depression produced by the heat  The indoor air is forced to pass through the air gap due to the depression produced by the heat 3/h. The air through the gap warms due to the solar  exchanger. The airflow rate is fixed equal to 45 m exchanger. The airflow rate is fixed equal to 45 m3 /h. The air through the gap warms due to the solar radiation effect; the exchanger allows the recovery of this load with a pre‐heating action on the inlet  radiation effect; the exchanger allows the recovery of this load with a pre-heating action on the inlet air air from the outside, as shown in Figure 3.  from the outside, as shown in Figure 3.

  Figure 3. (a) Section of the overall system; (b) Section of the air flow through the air gap. Figure 3. (a) Section of the overall system; (b) Section of the air flow through the air gap. 

The flows through the heat exchanger are represented as follows:  The flows through the heat exchanger are represented as follows: •  •  •

 •

point 1 is the inlet airflow from the outside;  point 1 is the inlet airflow from the outside; point 2 is the heat recovery unit airflow to the inside;  point 2 is the heat recovery unit airflow to the inside; point 3 is the intake airflow of the heat recovery unit from the inside, after passing through the  point 3 is the intake airflow of the heat recovery unit from the inside, after passing through the ventilated gap of the window;  ventilated gap of the window; point 4 represents the heat recovery unit airflow to the outside.  point 4 represents the heat recovery unit airflow to the outside. The experiment was carried out with different configurations, as shown in Table 1.  The experiment was carried out with different configurations, as shown in Table 1. Table 1. Configurations.  Table 1. Configurations.

Code 

Heating On  Heating Cooling  Off  Heating On Comfort  Off  Cooling Off Heating  Code

Comfort

Off

Cooling Heat Exchanger Off  On Exchanger Cooling Heat On  On On Off Off  On On On Off

On

2.2. Calibration of the Test Cells  2.2. Calibration of the Test Cells A  preliminary  step  of  calibration  of  the  thermal  losses  of  the  cells  was  required  to  correctly  proceed  with  the  experimental  campaign,  aimed losses at  verifying  their  thermo‐physical  behavior.  The  A preliminary step of calibration of the thermal of the cells was required to correctly proceed calibration was made before the glazing systems were mounted and the south faces of the cells were  with the experimental campaign, aimed at verifying their thermo-physical behavior. The calibration made  by  opaque  walls  with systems the  same  characteristics.  Figure  4  shows  the  of were the  calibration  was made before the glazing were mounted and the south faces ofresults  the cells made by phase in terms of cumulated consumption to the cumulated degree‐hours.  opaque walls with the same characteristics. Figure 4 shows the results of the calibration phase in terms The  almost  perfect  overlap  of  the  graphs  of  energy  consumption  implies  an  identical  energy  of cumulated consumption to the cumulated degree-hours. behavior between the cells.  The almost perfect overlap of the graphs of energy consumption implies an identical energy Once  verified,  analogy  of  the  energy  behavior,  the  related  test  windows  and  the  heat  behavior between thethe  cells. recovery  unit  in  the  C3  were  mounted.  The  calculation  of  windows the  flow  and rate the for heat each  cell,  in  Once verified, the analogy ofthen  the energy behavior, the related test recovery accordance with EN ISO 12569 [17], was carried out by linearizing the logarithm of the concentration  unit in the C3 were then mounted. The calculation of the flow rate for each cell, in accordance with difference of the sulfur hexafluoride (SF 6) gas between the end and the beginning of the sampling.  EN ISO 12569 [17], was carried out by linearizing the logarithm of the concentration difference of the Figure 5 shows the trend of the decay of the SF  over a period of 7 h: in blue, the cyclical activation of  sulfur hexafluoride (SF6 ) gas between the end 6and the beginning of the sampling. Figure 5 shows the extractor (15 min per hour), in red the almost constant performance given by the heat recovery,  the trend of the decay of the SF6 over a period of 7 h: in blue, the cyclical activation of the extractor and the slope of the line represents the flow rate per hour. 

 

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5 of 14  in red the almost constant performance given by the heat recovery, and the slope of 5 of 14  the line represents the flow rate per hour.

    Figure 4. Calibration of energy consumption.  Figure 4. Calibration of energy consumption. Figure 4. Calibration of energy consumption. 

    Figure 5. Flow rate per hour. Figure 5. Flow rate per hour.  Figure 5. Flow rate per hour. 

3. Results and Discussion 3. Results and Discussion  3. Results and Discussion  3.1. Assessment of the Energy Consumption 3.1. Assessment of the Energy Consumption  3.1. Assessment of the Energy Consumption  The first phase of the test consists of the analysis of the energy consumption of the cells aimed The first phase of the test consists of the analysis of the energy consumption of the cells aimed  The first phase of the test consists of the analysis of the energy consumption of the cells aimed  at assessing the energy performance of the dynamic system compared to the traditional sample. In at assessing the energy performance of the dynamic system compared to the traditional sample. In  at assessing the energy performance of the dynamic system compared to the traditional sample. In  particular, energy consumption was analyzed following two different approaches: particular, the the  energy  consumption  was  analyzed  following  two methodological different  methodological  particular,  the  energy  consumption  was  analyzed  following  two  different  methodological  ‚approaches:  Cumulated consumption; approaches:  ‚ Energy Signature method. Cumulated consumption;   Cumulated consumption;  Energy Signature method.  The Energy Signature (ES) method, described in Annex B of the international standard  Energy Signature method.  EN 15603:2008 [18],Signature  is traditionally assess the overall energy behavior of a buildingstandard  [19–21].   The  Energy  (ES)  applied method, todescribed  in  Annex  B  of  the  international  The  Energy  Signature  (ES)  method,  in  Annex  the  the international  standard    In the present work the method is used as andescribed  indirect empirical toolB toof  assess energy performance EN 15603:2008 [18], is traditionally applied to assess the overall energy behavior of a building [19– EN 15603:2008 [18], is traditionally applied to assess the overall energy behavior of a building [19– of theIn  dynamic system [22]. the  The method  ES of buildings is as  an an  assessment in which energy consumption 21].  the  present  work  is  used  indirect method empirical  tool  to  assess  the  energy  21].  In  the  present  work  the  method  is  used  as  an  indirect  empirical  tool  to  assess  the  energy  is correlated with climatic variables; it represents the of  actual energyis  behavior of the building. Itin  consists performance  of  the  dynamic  system  [22].  The  ES  buildings  an  assessment  method  which  performance  of  the  dynamic  system  [22].  The  ES  of  buildings  is  an  assessment  method  in  which  energy consumption is correlated with climatic variables; it represents the actual energy behavior of  energy consumption is correlated with climatic variables; it represents the actual energy behavior of  the  building.  It  consists  of  a  graphical  representation  of  the  power  or  energy  consumption  of  a  the  building.  It  consists  of  a  graphical  representation  of  the  power  or  energy  consumption  of  a  building (heating, cooling, hot water, etc.) as a function of external parameters (usually the outdoor  building (heating, cooling, hot water, etc.) as a function of external parameters (usually the outdoor 

 

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of aBuildings 2016, 6, 3  graphical representation of the power or energy consumption of a building (heating, cooling, 6 of 14  hot water, etc.) as a function of external parameters (usually the outdoor air temperature). In an outdoor temperature-power graph,temperature‐power  the slope of the curve represents theof overall heatrepresents  loss coefficient air  temperature).  In  an  outdoor  graph,  the  slope  the  curve  the  of the building. The ES is also used to evaluate the thermal performance of building components in overall heat loss coefficient of the building. The ES is also used to evaluate the thermal performance  of  building  components  operational  conditions that [22], inbased  on  the  assumption  that  in  same  operational conditions [22], in  based on the assumption the same outdoor conditions thethe  difference outdoor conditions the difference in energy performance is due to the physical characteristics of the  in energy performance is due to the physical characteristics of the elements under evaluation. elements under evaluation.  The cumulated consumption and the ES of the test cells have been evaluated in the periods shown in TableThe  2. cumulated  consumption  and  the  ES  of  the  test  cells  have  been  evaluated  in  the  periods  shown in Table 2.  Table 2. Heating and cooling periods and weather data. The period of diurnal average of solar radiation Table  2. 11 Heating  cooling  periods  and  data.  The  period  diurnal  average  of  solar  is: (a) from a.m. toand  4 p.m.; (b) from 8 a.m. toweather  6 p.m.; (c) from 8 a.m. to 9of p.m. radiation is: (a) from 11 a.m. to 4 p.m.; (b) from 8 a.m. to 6 p.m.; (c) from 8 a.m. to 9 p.m.  External Temperature (˝ C)

External Temperature (°C) Configuration  Period  MinMin Max Avg Max Avg (a) Heating February ´3.91−3.91  12.87 2.88 (a) Heating 7 January–11 7 January–11 February 12.87  2.88  (b) Heating 4–30 April 0.9 0.9  29.16 14.51 (b) Heating  4–30 April  29.16  14.51  (c) Cooling 1–21 July 10.9710.97  34.88 24.51 (c) Cooling  1–21 July  34.88  24.51 

Configuration

Period

Solar Radiation (W/m2 )

Solar Radiation (W/m2) Max Avg Max  Avg 552 192 552  192  915 371 915  371  955 491 955  491 

3.1.1. Heating Configuration  3.1.1. Heating Configuration Figure 6 shows the cumulated consumption of the test cells detected in configuration (a) and (b)  Figure 6 shows the cumulated consumption of the test cells detected in configuration (a) and (b) of  Table  2.  The overall overall energy energy  consumption consumption  of  lower  than  C2  in  periods.  In  of Table 2. The ofC3  C3is isconstantly  constantly lower than C2both  in both periods. particular,  in  configuration  (a)  the  consumption  of  C3  is,  on  average,  20%  lower  than  C2,  with  a  In particular, in configuration (a) the consumption of C3 is, on average, 20% lower than C2, with cumulated difference difference  equal equal  to to  109 109  kWh. kWh.  In  a cumulated In configuration  configuration (b),  (b), characterized  characterizedby  byhigher  higherexternal  external temperatures,  the  energy  behavior  of  the  test  cells  diverges  to  a  greater  extent  and  the  mean  temperatures, the energy behavior of the test cells diverges to a greater extent and the mean percentage percentage difference increases up to about 30% with peaks exceeding 40%.  difference increases up to about 30% with peaks exceeding 40%.

 

  Figure 6. Cumulated consumption: (a) configuration “a” of Table 2; (b) configuration “b” of Table 2.  Figure 6. Cumulated consumption: (a) configuration “a” of Table 2; (b) configuration “b” of Table 2. 

 

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This  trend  trend  is  is  better  better  explained  explained  by  by  observing  observing  in  in  more  more  detail  detail  the  the  cells’  cells’  consumption  consumption  in  in  absolute  absolute  This  This trend is better explained by observing in more detail the cells’ consumption in absolute terms: the greatest energy savings and the lowest percentage difference are detected in the first period,  terms: the greatest energy savings and the lowest percentage difference are detected in the first period,  terms: the greatest energy savings and the lowest percentage difference are detected in the first period, which is much cooler, and vice versa, the lowest energy savings, in absolute value, and the greatest  which is much cooler, and vice versa, the lowest energy savings, in absolute value, and the greatest  which is much cooler, and vice versa, the lowest energy savings, in absolute value, and the greatest percentage difference are detected in the second period, which is much warmer.  percentage difference are detected in the second period, which is much warmer.  percentage difference are detected in the second period, which is much warmer. The dynamic system allows a lower utilization of the heating plant, especially in the warmer  The dynamic system allows a lower utilization of the heating plant, especially in the warmer  The dynamic system allows a lower utilization of the heating plant, especially in the period.  period.  warmer period. The combined system is compared with individual operations, ventilated windows or the heat  The combined system is compared with individual operations, ventilated windows or the heat  The combined system is compared with individual operations, ventilated windows or the heat recovery  unit  unit  alone.  alone.  In  In  the  the  former  (Figure  (Figure  7),  the  the  system  aims  aims  at  saving  saving  about  13%  13%  of  the  the  energy  energy  recovery  recovery unit alone. In the former  former (Figure 7),  7), the system  system aims at  at saving about  about 13% of  of the energy compared to C2.  compared to C2.  compared to C2.

  Figure 7. Energy consumption referring to the operation of the ventilated window alone, in winter.  Figure 7. Energy consumption referring to the operation of the ventilated window alone, in winter. Figure 7. Energy consumption referring to the operation of the ventilated window alone, in winter. 

In the latter (Figure 8), the overall consumption of C3 is lower than that detected for C2, which  In the latter (Figure 8), the overall consumption of C3 is lower than that detected for C2, which  In the latter (Figure 8), the overall consumption of C3 is lower than that detected for C2, which is is about 20%. The heat recovery unit alone would seem to achieve the same energy savings obtained  is about 20%. The heat recovery unit alone would seem to achieve the same energy savings obtained  about 20%. The heat recovery unit alone would seem to achieve the same energy savings obtained by the combined system. This condition occurs only for certain ranges of external temperature, as is  by the combined system. This condition occurs only for certain ranges of external temperature, as is  by the combined system. This condition occurs only for certain ranges of external temperature, specified in more detail in the paragraph on the efficiency of the system.  specified in more detail in the paragraph on the efficiency of the system.  as is specified in more detail in the paragraph on the efficiency of the system.

  Figure 8. Energy consumption referring to the operation of the heat recovery unit alone, in winter.  Figure 8. Energy consumption referring to the operation of the heat recovery unit alone, in winter. Figure 8. Energy consumption referring to the operation of the heat recovery unit alone, in winter. 

The comparison of the ES of the cells (Figure 9a) shows a better energy behavior of C3 than C2,  The comparison of the ES of the cells (Figure 9a) shows a better energy behavior of C3 than C2,  The comparison of the ES of the cells (Figure 9a) shows a better energy behavior of C3 than C2, confirming the performance of the dynamic system both in terms of heat losses (related to the slope  confirming the performance of the dynamic system both in terms of heat losses (related to the slope  confirming the performance of the dynamic system both in terms of heat losses (related to the slope of of the straight lines) and of switch‐off temperature of the heating system (intersection of the straight  of the straight lines) and of switch‐off temperature of the heating system (intersection of the straight  the straight lines) and of switch-off temperature of the heating system (intersection of the straight line line with the x‐axis). The slope and the switch‐off temperature of C3 are about 3.5 W/K and 2 °C lower  line with the x‐axis). The slope and the switch‐off temperature of C3 are about 3.5 W/K and 2 °C lower  with the x-axis). The slope and the switch-off temperature of C3 are about 3.5 W/K and 2 ˝ C lower than than those of C2, respectively. These results demonstrate that the combined system reduces the heat  than those of C2, respectively. These results demonstrate that the combined system reduces the heat  those of C2, respectively. These results demonstrate that the combined system reduces the heat losses of losses  of  of  the window.  the window.  In  In  fact,  fact,  the  the  surface  surface  temperature  temperature  of  of  the  the  inner  inner  glass is  glass is  maintained as  maintained as  close  close  as  as  losses    

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possible to the temperature of the indoor environment. This action involves a reduction of the thermal  the window. In fact, the surface temperature of the inner glass is maintained as close as possible to the transmittance of the component as a function of the increasing flux in the air gap [13]. Moreover, the  temperature of the indoor environment. This action involves a reduction of the thermal transmittance heat  exchanger  at  more  temperatures  in  Moreover, the  following  psychrometric  of the componentworks  as a function offavorable  the increasing flux in theas  airshown  gap [13]. the heat exchanger analyses.  works at more favorable temperatures as shown in the following psychrometric analyses.

 

  Figure  9. 9.  Energy  ventilation  rate  equal  to  to 45  45 m3/h;  (b)  Figure EnergySignature  Signatureof  ofheating  heatingconfiguration:  configuration:(a) (a) ventilation rate equal m3 /h; 3 3 ventilation rate equal to 60 m (b) ventilation rate equal to 60 /h.  m /h.

An  increase  of  the  ventilation  rate  (Figure  9b)  determines  the  increase  of  the  percentage  An increase of the ventilation rate (Figure 9b) determines the increase of the percentage difference difference of the two test cells. The energy behavior of C3 is further improved than that of C2. This is  of the two test cells. The energy behavior of C3 is further improved than that of C2. This is due to due to the performance of the two single components, the glazing system and heat recovery unit,  the performance of the two single components, the glazing system and heat recovery unit, which are which are more efficient with the increasing of the airflow rate [8]. In C3, the increasing of the airflow  more efficient with the increasing of the airflow rate [8]. In C3, the increasing of the airflow rate, which rate, which involves greater ventilation losses, is balanced by the combined action of the dynamic  involves greater ventilation losses, is balanced by the combined action of the dynamic system. In C2, system.  In  C2,  the  ventilation  losses  are  not  recovered,  with  a  consequent  increase  of  the  overall  the ventilation losses are not recovered, with a consequent increase of the overall consumption. consumption.  3.1.2. Cooling Configuration 3.1.2. Cooling Configuration  Figure 10 shows the trend of the cumulated consumption of the test cells in configuration (c). Figure 10 shows the trend of the cumulated consumption of the test cells in configuration (c). C3  C3 has the best energy behavior and the lowest consumption, both in percentage (about 13%) and in has the best energy behavior and the lowest consumption, both in percentage (about 13%) and in  absolute terms (about 25 kWh) compared to C2. However, in the cooling phase, the combination of the absolute terms (about 25 kWh) compared to C2. However, in the cooling phase, the combination of  dynamic glazing and the heat recovery unit does not allow the flux to be optimally managed, because the dynamic glazing and the heat recovery unit does not allow the flux to be optimally managed,  the exhaust air that comes into the exchanger from the indoor environment transfers heat to the inlet because the exhaust air that comes into the exchanger from the indoor environment transfers heat to  air, warming it. The following psychrometric analyses show the behavior of the coupled system from the  inlet air, warming  it. The  following  psychrometric  analyses show  the  behavior  of  the  coupled  a physical-technical point of view. system from a physical‐technical point of view. 

 

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   Figure 10. Cumulated consumption of cooling configuration (c) of Table 2.  Figure 10. Cumulated consumption of cooling configuration (c) of Table 2. Figure 10. Cumulated consumption of cooling configuration (c) of Table 2. 

In  the  cooling  season,  reduction  of  the  consumption  due  only  to  the  dynamic  glazing  In  the the  cooling cooling  season, season,  the  the  reduction reduction  of of  the the  consumption consumption  is  is  due due  only only  to to  the the dynamic dynamic  glazing glazing  In the is (Figure 10).  (Figure 10).  (Figure 10). On  the  contrary,  combined  system  less  when  the  summer  On the the contrary, contrary,  the  combined  system  is efficient less  efficient  efficient  when  compared  compared  with  the operation summer  On thethe  combined system is lessis  when compared with the with  summer operation of the ventilated window with the activation of the bypass (Figure 11). In this case, C3 saves  operation of the ventilated window with the activation of the bypass (Figure 11). In this case, C3 saves  of the ventilated window with the activation of the bypass (Figure 11). In this case, C3 saves about about 33% of energy compared to C2.  about 33% of energy compared to C2.  33% of energy compared to C2.

   Figure 11. Energy consumption referring to the operation of the ventilated window alone, in summer. Figure 11. Energy consumption referring to the operation of the ventilated window alone, in summer.  Figure 11. Energy consumption referring to the operation of the ventilated window alone, in summer. 

Similarly  to  the  heating  configuration,  is  to  the  of  Similarly to to the the  heating  configuration,  it possible is  possible  possible  to  analyze  analyze  the  behavior  behavior  of  the  the  dynamic  dynamic  Similarly heating configuration, it isit  to analyze the behavior of the dynamic system system through the Energy Signature method.  system through the Energy Signature method.  through the Energy Signature method. The  outcome  of  the  cumulative  consumption  the  assessment  the  The  outcome outcome  of of  the the  cumulative cumulative  consumption consumption  analysis  analysis  is  confirmed  by  by  the the  assessment assessment  of  of  the the  The analysis is  is confirmed  confirmed by of Energy Signature. The comparison, in fact, shows both a lower slope and a downward translation of  Energy Signature. The comparison, in fact, shows both a lower slope and a downward translation of  Energy Signature. The comparison, in fact, shows both a lower slope and a downward translation of the Energy Signature of C3 with respect to C2, due to a better management of the thermal loads of  the Energy Signature of C3 with respect to C2, due to a better management of the thermal loads of  the Energy Signature of C3 with respect to C2, due to a better management of the thermal loads of the the combined system compared to the reference one (Figure 12).  the combined system compared to the reference one (Figure 12).  combined system compared to the reference one (Figure 12).

  

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  Figure 12. Energy Signature of cooling configuration.  Figure 12. Energy Signature of cooling configuration.

  3.2. Thermal Comfort Evaluation  3.2. Thermal Comfort Evaluation Figure 12. Energy Signature of cooling configuration.  The psychrometric analyses [23], particularly focused on the environment line and the straight  The psychrometric analyses [23], particularly focused on the environment line and the straight patterns of the transforms, allow the evaluation and the interpretation of the results from a thermal  3.2. Thermal Comfort Evaluation  patterns of the transforms, allow the evaluation and the interpretation of the results from a thermal efficiency and comfort perspective.  efficiency and comfort perspective. The psychrometric analyses [23], particularly focused on the environment line and the straight  During the winter testing period, the indoor environmental monitoring data show the positive  During the winter testing period, the indoor environmental monitoring data show the positive patterns of the transforms, allow the evaluation and the interpretation of the results from a thermal  synergy between the dynamic system and the heat recovery unit, which confirms the above energy  efficiency and comfort perspective.  synergy between the dynamic system and the heat recovery unit, which confirms the above energy consumption data.  During the winter testing period, the indoor environmental monitoring data show the positive  consumption data. Figure 13 shows the points of the transform of the thermal cycle of the heat exchanger:  synergy between the dynamic system and the heat recovery unit, which confirms the above energy  Figure 13 shows the points of the transform of the thermal cycle of the heat exchanger:  consumption data.  segments 1–2 represent the process of the heat exchange from outside to inside by the recovery  unit that exchanges heat with outgoing airflow;  ‚ segments 1–2 represent the process of the heat exchange from outside to inside by the recovery Figure 13 shows the points of the transform of the thermal cycle of the heat exchanger:   unit segment 2–3’ show the process of heating or cooling of the internal ambient by the plant;  that exchanges heat with outgoing airflow;  segments 1–2 represent the process of the heat exchange from outside to inside by the recovery  segment 3’–3 are the overheating of the ambient air passing through the ventilated gap of the  ‚  segment 2–3’ show the process of heating or cooling of the internal ambient by the plant; unit that exchanges heat with outgoing airflow;  window;  ‚ segment 3’–3 are the overheating of the ambient air passing through the ventilated gap of  segment 2–3’ show the process of heating or cooling of the internal ambient by the plant;    segment 3–4 indicate  the process  of  the  heat  exchange  of  the air  from  the  inlet  airflow  in the  segment 3’–3 are the overheating of the ambient air passing through the ventilated gap of the  the window; recovery unit to outside giving heat incoming airflow.  window;  ‚ segment 3–4 indicate the process of the heat exchange of the air from the inlet airflow in the  segment 3–4 indicate  the process  of  the  heat  exchange  of  the air  from  the  inlet  airflow  in the  recovery unit to outside giving heat incoming airflow. recovery unit to outside giving heat incoming airflow. 

    Figure  13.  Psychrometric  chart—thermodynamic  transforms:  (red  lines)  “Heating”—22  April  at  12  p.m.—and (blue lines) “Cooling”—3 July at 12 p.m.  Figure  13.  Psychrometric  chart—thermodynamic  transforms:  (red  lines)  “Heating”—22  April  12  at Figure 13. Psychrometric chart—thermodynamic transforms: (red lines) “Heating”—22at April p.m.—and (blue lines) “Cooling”—3 July at 12 p.m.  12 p.m.—and (blue lines) “Cooling”—3 July at 12 p.m.

   

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During the tests in winter (Figure 13, red lines), besides the energy advantage generated by the heat recovery operation, the air passing through the gap of the ventilated window overheats (3’–3) by increasing the heat exchange of the outgoing airflow with the incoming one. The higher temperature difference between the airflows (3’–3) increases the energy efficiency of the overall system with respect to the theoretical operation of the heat recovery alone (2–3), allowing the achievement of the set point conditions with a reduced energy expenditure by the heating system. The considerations in the summer season are different (Figure 13, blue lines). The operation of the ventilated window involves a daily overheating of the pre-treated air through the gap (3’–3), reducing the heat recovery unit efficiency. In fact, the ventilated window defines a smaller difference of temperature (3–4) than the difference of temperature that would obtain with the exchanger alone (theoretical 3’–4). 3.3. Efficiency of the Coupled System In this section, the improvement of the performance of the energy recovery unit is shown as a result of the pre-heating of the air through the gap of the ventilated window. The nominal efficiency of the heat exchanger, declared by the manufacturer, is a function of the variable airflow rate. The flow rate limit for experimentation is equal to 45 m3 /h with an efficiency between 94% and 95%. The coupled system takes an important role in the heat flow management by developing three actions, the last of which is dependent on the previous, as in following: ‚ ‚ ‚

heat recovery; heat exchange reduction; integrated action of pre-heating in the dynamic windows before the heat recovery unit.

The first action takes place in the heat recovery unit: in winter, the exhaust hot air, outgoing from the air conditioner, exchanges heat with the cold air inlet. The two next actions take place at the level of the ventilated window. The passing of the air through the ventilated air gap allows the surface temperature of the inner glass to be maintained as close as possible to the internal air temperature; the thermal transmittance of the glass is reduced, increasing the air flow in the gap [12]. The solar radiation through the transparent component preheats the air that crosses the air gap even before it can reach the heat recovery unit [24]. As is known, the performance of the integrated system varies depending on weather conditions; therefore, the following charts show the trends of energy efficiency of the dynamic system. The performance cannot reportable through the single formulation of the efficiency of the exchanger but it was used for the broader definition of energy efficiency of the coupled system (Equation (1)), as follows: pTair,in ´ Text q η“ (1) pTint ´ Text q where: Tair,in is the temperature of inlet air in the recovery system (point 3 in Figure 3); Text is the external temperature (point 1 in Figure 3); Tint is the internal temperature of the cell. The dynamic system performance is heavily dependent on the external temperature trend and the internal air temperature incoming to the heat recovery unit, preheated from the ventilated window. As can be seen for external temperatures between about 10 ˝ C and 22 ˝ C (Figure 14a), the combined action of the exchanger and the ventilated window increases the efficiency of the system with increasing external temperature and intake flow temperature, starting from an efficiency of 0.9 until about 3. When the external temperature goes below 10 ˝ C, the benefit of the ventilated window is irrelevant because the efficiency of the coupled system is similar to the efficiency of the

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heat recovery unit alone. Above 22 instead, the yield is opposite, decreasing with increasing recovery  unit  alone.  Above  22  °C,  instead,  the  yield  is  opposite,  decreasing  with  increasing  temperatures (Figure 14b). temperatures (Figure 14b). 

 

  Figure 14. Behavior of energy efficiency of the system in function of: (a) external temperature below Figure 14. Behavior of energy efficiency of the system in function of: (a) external temperature below  20 ˝ C; (b) external temperature above 20 ˝ C. 20 °C; (b) external temperature above 20 °C. 

In summer, the ventilated window alone would save up to 33% of the energy supplied by the  In summer, the ventilated window alone would save up to 33% of the energy supplied by the heat pump (Figure 9), but with the activation of the heat recovery unit the energy saving decreases  heat pump (Figure 9), but with the activation of the heat recovery unit the energy saving decreases to to 13% (Figure 8), due to the overheating of the outgoing air.  13% (Figure 8), due to the overheating of the outgoing air. The system does not work in an optimal way for temperatures higher than 22 °C because the  The system does not work in an optimal way for temperatures higher than 22 ˝ C because the heat heat  recovery  is  managed  by  algorithms  optimized  to  work  The  heat  recovery  unit  recovery unit isunit  managed by algorithms optimized to work alone. Thealone.  heat recovery unit integrates a integrates a system that allows the inlet air to bypass the heat exchanger under certain environmental  system that allows the inlet air to bypass the heat exchanger under certain environmental conditions. conditions. Specifically, the bypass is activated when the outside temperature (T 1) is simultaneously  Specifically, the bypass is activated when the outside temperature (T1 ) is simultaneously less than the less than the internal temperature (T int), and greater than that of the setting (T set = 20 °C) or when T internal temperature (Tint ), and greater than that of the setting (Tset = 20 ˝ C) or when T1 is greater than1  is greater than 18 °C and even greater than T int and T  is less than T set.  18 ˝ C and even greater than Tint and Tint is less than int Tset . In fact, the temperature of the inlet air to the unit (point 3 in Figure 7) is higher than the outlet  In fact, the temperature of the inlet air to the unit (point 3 in Figure 7) is higher than the outlet air air temperature. If there is no overheating (segment 3’–3), the recovery unit would work properly.  temperature. If there is no overheating (segment 3’–3), the recovery unit would work properly. 4. Conclusions 4. Conclusions  The improving effect of the ventilation on the total heat transfer of the dynamic window has been The improving effect of the ventilation on the total heat transfer of the dynamic window has  subject to analysis of a previous publication [13]. Starting the achieved results, we proposed an been  subject  to  analysis  of  a  previous  publication  [13]. from Starting  from  the  achieved  results,  we  upgrade of the system consisting of the ventilated window coupled with a heat recovery unit. This proposed an upgrade of the system consisting of the ventilated window coupled with a heat recovery  article analyzes the behavior of this dynamic system and the thermal comfort reachable in operating unit. This article analyzes the behavior of this dynamic system and the thermal comfort reachable in  conditions, typically in an office. operating conditions, typically in an office.  The results of the experimentation show that the combined system provides good performance  in  terms  of  energy  saving  with  respect  to  a  traditional  window,  especially  in  winter.  The 

 

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The results of the experimentation show that the combined system provides good performance in terms of energy saving with respect to a traditional window, especially in winter. The improvement is visible both at outdoor temperatures less than about 10 ˝ C (in January) and at warmer temperatures until about 22 ˝ C (in April) with an energy saving of about 20% and 40%, respectively. This effect is due to both the pre-heating of the air through the air gap and the operation of the heat exchanger. In particular, in the warmest winter period, higher external temperature, between about 10˝ and 22 ˝ C, allows the increase of the efficiency of the heat exchanger with a consequent higher energy saving. The sum of the energy savings achieved in winter with the operation of the dynamic window alone from one side, and of only the heat recovery unit from the other side, should allow it to reach a 33% energy savings. The experimental results show that at certain periods of the year the efficiency of the energy saving improves. The experimental results show that in any period of the year the efficiency of the coupled unit is better than the single system, reaching about 40% energy savings. Conversely, in summer, the energy savings of the combined system decreases to about 13%. This result is obtained thanks to the reduction of heat losses of the ventilated window that compensates the negative efficiency of the heat recovery unit. In fact, the energy savings of the ventilated window alone would be about 20%. A new specific algorithm of operation should exclude the heat recovery for temperatures higher than 20˝ C in order to maintain high values of performance in any condition. The good results obtained by the experimental campaign make the thus far analyzed dynamic system a good technology for energy saving in the office refurbishments sector. The proposed system is easily employable in building renovation in the tertiary sector, especially in office buildings, and represents a good compromise between cost of intervention, invasiveness of construction and energy savings. In such intended use, the indoor environment is occupied during the day when the system ensures greater efficiency. Analyses in real buildings are the future challenges both in terms of energy performance and architectural integration. Acknowledgments: This work was carried out according to an industrial research project with the VetroVentilato company. Author Contributions: The work presented in this paper is a collaborative development by all of the authors. In particular, Italo Meroni has performed the description of the cells. Francesco Salamone has performed the calibration of the test cells. Lorenzo Belussi has performed the assessment of the energy consumption. Benedetta Barozzi has performed the assessment of the thermal comfort. Ludovico Danza has performed the analysis of the efficiency of the system. Conflicts of Interest: The authors declare no conflict of interest.

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Torcal, F.P.; Mistretta, M.; Kaklauskas, A.; Granqvist, C.G. Nearly Zero Energy Building Refurbishment—A Multidisciplinary Approach; Springer: London, UK, 2013. Popescu, D.; Bienert, S.; Schutzenhofer, C.; Boazu, R. Impact of energy efficiency measures on the economic value of buildings. Appl. Energy 2012, 89, 454–463. [CrossRef] Xing, Y.; Hewitt, N.; Griffiths, P. Zero carbon buildings refurbishment—A hierarchical pathway. Renew. Sustain. Energy Rev. 2011, 15, 3229–3236. [CrossRef] Directive 2012/27/EU of the European Parliament and of the Council of 25 October 2012 on Energy Efficiency, Amending Directives 2009/125/EC and 2010/30/EU and Repealing Directives 2004/8/EC and 2006/32/EC; The European Parliament and of the Council: Brussels, Belgium, 2012. Data Elaborated from IEA Statistics. Available online: http://www.iea.org/ (accessed on 12 December 2015). Kneifel, J. Life-cycle carbon and cost analysis of energy efficiency measures in new commercial buildings. Energy Build. 2010, 42, 333–340. [CrossRef] Pérez-Lombard, L.; Ortiz, J.; Pout, C. A review on buildings energy consumption information. Energy Build. 2008, 40, 394–398. [CrossRef]

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