# Experimental Evaluation of the Heat Balance of an Interactive Glass Wall in A Heating Season

## Abstract

**:**

## 1. Introduction

## 2. IGW Prototype Design and Test Method

#### 2.1. Description of the Tested Prototype

_{g}= 0.5 W/m

^{2}K (gain factor g = 0.55, emissivity e = 0.92). To facilitate the solar radiation access inside the components and intensify heat transfer to the building, the central unit was made in the louver window technology. The absorbers made of perforated black sheet (absorption coefficient α = 0.95) were attached to the swivelling louver panels so that, after swivelling the panels, the absorber was exposed as vertically to the sunlight rays as possible. The operation of the glass panels swivelling was made automatic by connecting the actuator that regulates the swivelling with a controller responding to air temperature and solar irradiance I

_{g}measured in the space between the glazed units. The threshold values were adopted at 20 °C for the temperature T

_{1}of the air in the space between the glazed units and 50 W/m

^{2}for the solar irradiance I

_{g}measured behind the outer glazing.

_{fus}= 220–225 J/g, m.p. = 28 °C and solidification temperature = 21 °C was used.

#### 2.2. Description of Test Stand

_{i}in field conditions. The prototype of the IGW of dimensions 890 × 885 mm was installed in a facing south wall of the test chamber (Figure 5). It was thermally separated from the wall in which it was fixed by means of extruded polystyrene layer 0.08 m thick and polyurethane foam.

^{2}) interacting with 16 Channel Data Acquisition Monitoring System Comet MS6D. The arrangement of the sensors is shown in Figure 4 and Figure 6. The data were recorded with the frequency of every five minutes. The louver was controlled by MP018 Relays Module Output interacting with the Comet recorder. List of the employed apparatus and sensors together with their measurement accuracy has been listed in Table 1.

#### 2.3. Description of the Method for the Evaluation of IGW Thermal Efficiency

_{i}taken at, for instance, its inner surface. It is a resultant of the flow connected with heat loss q

_{H}, and the flow coming from solar radiation q

_{S}:

_{H}is determined by the wall thermal resistance R

_{IGH}and difference between the temperature of air on its sides:

- R
_{IGW}—total thermal resistance of IGW ((m^{2}·K)/W), - U
_{IGW}—heat transfer coefficient of IGW (W/(m^{2}·K)), - ΔT—temperature difference on the wall’s sides.

_{IGW_EMP}can be determined:

_{S}is determined by solar irradiance and the properties of the wall in the aspect of heat transfer indoor. A significant amount of the absorbed heat is lost as an effect of additional losses resulting from the increase of the wall temperature. The absorption of sunlight after the time necessary for heat flow transfer to the inner surface results in a reduction of flow q

_{i}, from the value q

_{H}(Equation (3)) to a level proportional to the amount of the energy absorbed. Consequently, solar gains Q

_{S}in the time interval of (t1:t2) can be calculated from the equation:

- A—total pane area (m
^{2}).

_{SHGU}referred to the sum of solar irradiance transferred through the outer glazing S

_{g}in IGW balance, can be calculated from the equation:

- C
_{g}—ratio of the outer glazing visible area (not covered by the glazing bead) to the total glazing inner area IGW (C_{g}= 0.89), - S
_{g}—the sum of solar irradiance transferred through the outer glazing (Wh/m^{2}).

## 3. Results and Discussion

_{IGW_EMP}was determined.

#### 3.1. Empirical Heat Transfer Coefficient U_{IGW}

_{max}) corresponding to the maximum thermal resistance of IGW was identified (Figure 8, Table 1). From the turn of February and March 2019 tests were conducted with the blocked open inner louver. From this period data that were used for the identification of heat transfer coefficient U(R

_{min}) corresponding to a reduced value of thermal resistance of IGW were selected (Table 2).

_{H(U)}connected with the heat loss proportional to air temperature difference ΔT on both sides of the wall, which can be expressed with a formula (Equation (8)).

#### 3.2. Determination of the Solar Heat Gain Utilisation Efficiency (η_{SHGU})

_{i}with flux q

_{u}calculated after Equation (7) for air temperature difference ΔT on both sides of the wall in a given time interval was a basis for the calculation of the actual solar gains Q

_{S}. The knowledge of solar gains referred to the sum of solar irradiance that generated these gains enables the estimation of the solar heat gain utilisation efficiency η

_{SHGU}in IGW (Equation (6)). The efficiency referred to the sum of solar irradiance transferred through the outer glazing S

_{g}, is expressed by the equation:

- ${I}_{g}[\frac{W}{{m}^{2}}]$—solar irradiation transferred through the outer glazing in time interval (t1:t2).

_{SHGU}using the dependencies described by Equations (8) and (9) the period of high sums of daily solar irradiation was selected (Figure 9).

_{SHGU}in IGW calculated from Equation (9) and its components are tabulated in Table 4.

#### 3.3. Validation of IGW Heat Balance Calculation Mode

_{i}) was compared with the balance calculated on the basis of the determined heat transfer coefficient U

_{IGH}and the efficiency of solar energy utilisation η

_{SHGU}.

_{i}(Equation (2)) with the balance Q

_{H}calculation based on heat transfer coefficient U

_{IGW}(Equations (7) and (8)), and the solar gain Q

_{S}calculation based on solar heat gain utilisation efficiency η

_{SHGU}in IGW (Equation (9)) referred to the sum of solar radiation recorded behind the glazing. The calculation results are tabulated in Table 5.

_{IGW}and solar heat gain utilisation efficiency η

_{SHGU}is 15.53%. This difference indicates that either the solar gains component is underestimated or the heat loss component overestimated. In the context of the calculations of the potential solar irradiation derived heat gains the difference is on the margin of calculations safety.

#### 3.4. Prediction of IGW Heat Balance in a Heating Season Based on Climate Database

- A—surface of IGW (1 m
^{2}), - U
_{IGW}—heat transfer coefficient (after Equation (7)), - T
_{i}—indoor air temperature (Ti = 20 °C)], - S
_{eh}—hourly sum of solar irradiation recorded in front of the glazing, - g—gain factor (g = 0.55 according to the manufacturer’s specifications of the glazing used).

_{gh}can be determined:

^{2}in each month of the heating season are tabulated in Table 6 and Figure 11. The Negative values indicate the overbalance of heat gains over losses.

^{2}. It is a value ten times lower than the solar radiation transferred through the outer glazing. This property is significant for the occupants’ comfort.

## 4. Conclusions

- (1)
- The prediction of heat balance calculated for a heating season for a selected locality indicated the overbalance of heat gains over losses in all the months of the season when the IGW was oriented to the south, south-east and south-west. The western and eastern orientations in November and December resulted in the predominance of heat losses.
- (2)
- The tests indicated that, unlike conventional windows, apart from transparency, owing to the use of phase-change materials (PCM) in the IGW structure, it has the capacity of giving up heat gains even eight hours after the sunset.
- (3)
- The test results confirm the potential of the interactive designs, which apart from transparency, have the capacity to reduce the conventional energy demand and exert a favourable impact on the functionality of a building and occupants’ comfort. The use of cutting-edge technologies and their increasing availability for the shaping of the outer envelope of a building opens up new possibilities of construction engineering.
- (4)
- The validity of the method discussed in the paper indicated a difference in the heat balance calculated on the basis of the recorded heat flux density at the level of 15.53% of heat gains underestimation or its losses overestimation, which can be considered a result satisfactory with respect of calculations safety.

_{EMP}and η

_{USRH}presented in the paper should be regarded as one of the stages of the research. Further research is planned on a greater scale, in which special attention will be focused on the improvement of the thermal capacitance and optimization of glazing selection in order to increase heat gains and the capacity of their storage.

## 5. Patents

## Funding

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Thermal operation of passive walls: (

**a**) classic Trombe wall, (

**b**) composite Trombe wall with an insulating panel, (

**c**) composite Trombe wall with a selective absorber. 1—glazing, 2—massive wall, 3—insulating polystyrene wall, 4—insulating layer directly behind the selective absorber.

**Figure 2.**Water Trombe wall (transwall): 1—glass water container, 2—colored water, 3—diffusing-absorbing inserts.

**Figure 3.**The prototype of the tested interactive glass wall (IGW): 1—outer glazing, 2—louvers headrail, 3—swivelling louvers panels, 4—moveable absorber, 5—interior glazing, 6—louvers panels swivelling actuator, 7—containers with heat storing materials.

**Figure 4.**The prototype of the tested wall: 1—exterior glazing, 2—louvers headrail, 3—swivelling louvers panels, 4—moveable absorber, 5—interior glazing, 6—louvers panels swivelling actuator, 7—containers with heat storing materials containers, 8—aerogel mat seal, 9—relay rods, 10—temperature sensors, 11—density heat flux sensor, 12—pyranometers.

**Figure 5.**The chamber for field tests: 1—IGW module, 2—pyranometer (I

**) placed behind the exterior glazing, 3—pyranometer (I**

_{g}**) placed outside the chamber.**

_{e}**Figure 7.**Air temperature distribution vs. solar irradiance recorded outside the test chamber in analyzed period.

**Figure 8.**Distribution of outdoor air temperature (Te), heat flux density measured on the inner surface of the IGW and solar irradiance measured behind the outer glazing in the very low radiation period.

**Figure 9.**Distribution of air temperature outside the chamber Te, heat flux density measured on the IGW inner surface and solar irradiation measured behind the glazing in the period of considerable solar radiation.

**Figure 10.**Distribution of air temperature Te, heat flux density measured on the inner surface of the IGW and solar irradiation measured behind the outer glazing in January 2019.

**Figure 11.**Heat balance calculated for the months of the heating season depending on the orientation with respect to cardinal points chart.

Kind of Sensor | Type of Sensor | Accuracy |
---|---|---|

Temperature sensor | PT1000 | A class (<0.2 °C) |

Irradiaton sensor | DeltaOhm LP Pyra12 DeltaOhm LPPyra03 | <1 % (first class) <±0.2% (second class) |

Heat flow density | ALMEMO FQ A020 C | <6% of measured value |

Comet MS6D 16 Channel Data Acquisition Monitoring System | ||

DC | 4 to 20 mA | ±0.1% (±0.02 mA) |

DC | −10 V to +10 V | ±0.1% (±10 mV) |

Temperature | PT1000 | ±0.2 °C (−200 °C to +100 °C) |

**Table 2.**Averaged daily values of heat flux density, outdoor temperature and empirically determined heat transfer coefficient.

Number of Day | ${\overline{\mathit{q}}}_{\mathit{i}}[\frac{\mathit{W}}{{\mathit{m}}^{2}}]$ | $\overline{\Delta \mathit{T}}[{}^{\xb0}\mathit{K}]$ | ${\overline{\mathit{U}}}_{\mathit{E}\mathit{M}\mathit{P}}({\mathit{R}}_{\mathbf{max}})[\frac{\mathit{W}}{{\mathit{m}}^{2}\mathit{K}}]$ |
---|---|---|---|

1 | 3.409 | 20.70 | 0.165 |

2 | 3.685 | 20.67 | 0.178 |

3 | 3.425 | 20.12 | 0.170 |

4 | 3.375 | 20.16 | 0.167 |

5 | 3.242 | 20.02 | 0.162 |

Mean value $\overline{x}$ | 0.168 | ||

Standard deviation $\sqrt{\frac{\sum {(x-\overline{x})}^{2}}{(n-1)}}$ | 0.006 |

**Table 3.**Averaged daily values of heat flux density, outdoor air temperature and empirically determined heat transfer coefficient in “solar profit” mode.

Number of Day | ${\overline{\mathit{q}}}_{\mathit{i}}[\frac{\mathit{W}}{{\mathit{m}}^{2}}]$ | $\overline{\Delta \mathit{T}}[{}^{\xb0}\mathit{K}]$ | ${\overline{\mathit{U}}}_{\mathit{E}\mathit{M}\mathit{P}}({\mathit{R}}_{\mathbf{min}})[\frac{\mathit{W}}{{\mathit{m}}^{2}\mathit{K}}]$ |
---|---|---|---|

1 | 5.08 | 20.14 | 0.252 |

2 | 5.05 | 20.45 | 0.247 |

3 | 5.38 | 20.23 | 0.266 |

Mean value $\overline{x}$ | 0.255 | ||

Standard deviation $\sqrt{\frac{\sum {(x-\overline{x})}^{2}}{(n-1)}}$ | 0.01 |

**Table 4.**Daily sums of solar gains Qs, solar irradiance measured behind the outer glazing of IGW and calculated efficiency η

_{SHGU}.

Number of Day [n] | ${\mathit{Q}}_{\mathit{s}}[\frac{\mathit{W}\mathit{h}}{{\mathit{m}}^{2}}]$ | ${\mathit{S}}_{\mathit{g}}^{}[\frac{\mathit{W}\mathit{h}}{{\mathit{m}}^{2}}]$ | η_{SHGU} |
---|---|---|---|

10 | 131.61 | 608.1 | 21.64 |

11 | 276.60 | 1440.8 | 19.20 |

12 | 289.75 | 1398.1 | 20.73 |

13 | 249.51 | 1190.6 | 20.96 |

14 | 236.32 | 1143.3 | 20.67 |

15 | 104.56 | 438.6 | 23.84 |

Mean value $\overline{x}$ | 21.17 | ||

Standard deviation $\sqrt{\frac{\sum {(x-\overline{x})}^{2}}{(n-1)}}$ | 1.53 |

$\mathit{Q}\mathit{i}=\mathit{A}\cdot {\displaystyle \int {\mathit{q}}_{\mathit{i}}\mathit{d}\mathit{t}}$ | ${\mathit{Q}}_{\mathit{H}}=\mathit{A}\cdot {\displaystyle \int {\mathit{q}}_{\mathit{H}(\mathit{U})}\mathit{d}\mathit{t}}$ | ${\mathit{Q}}_{\mathit{S}}={\mathit{\eta}}_{\mathit{S}\mathit{H}\mathit{G}\mathit{U}}\cdot {\mathit{c}}_{\mathit{g}}\cdot \mathit{A}\cdot {\displaystyle \int {\mathit{I}}_{\mathit{g}}\mathit{d}\mathit{t}}$ | Q_{H}−Q_{S} | $\Delta \mathit{Q}=\frac{{\mathit{Q}}_{\mathit{i}}-({\mathit{Q}}_{\mathit{H}}-{\mathit{Q}}_{\mathit{S}})}{{\mathit{Q}}_{\mathit{i}}}\cdot 100\%$ |
---|---|---|---|---|

575.89 [Wh] | 3084.79 [Wh] | 2419.46 [Wh] | 665.33 [Wh] | 15.53% |

**Table 6.**Heat balance calculated for the months of the heating season depending on the orientation with respect to cardinal points.

Month | Heat Balance [Wh/m^{2}] | ||||
---|---|---|---|---|---|

E | SE | S | SW | W | |

October | −2442.03 | −3526.65 | −4226.97 | −3592.03 | −2492.84 |

November | 42.10 | −993.54 | −1691.16 | −1240.25 | −132.42 |

December | 835.30 | −237.27 | −841.21 | −390.31 | 727.05 |

January | 764.06 | −571.02 | −1160.47 | −421.21 | 870.04 |

February | −884.79 | −2124.54 | −2690.94 | −1839.41 | −692.03 |

March | −3260.19 | −4298.28 | −4679.78 | −3861.34 | −2921.9 |

April | −6536.78 | −7243.21 | −7272.98 | −6953.11 | −6259.6 |

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**MDPI and ACS Style**

Szyszka, J.
Experimental Evaluation of the Heat Balance of an Interactive Glass Wall in A Heating Season. *Energies* **2020**, *13*, 632.
https://doi.org/10.3390/en13030632

**AMA Style**

Szyszka J.
Experimental Evaluation of the Heat Balance of an Interactive Glass Wall in A Heating Season. *Energies*. 2020; 13(3):632.
https://doi.org/10.3390/en13030632

**Chicago/Turabian Style**

Szyszka, Jerzy.
2020. "Experimental Evaluation of the Heat Balance of an Interactive Glass Wall in A Heating Season" *Energies* 13, no. 3: 632.
https://doi.org/10.3390/en13030632