Study of Some Parameters Influence on a Saharian Building Balance Sheet

The heat balance corresponds roughly to heat inputs from outside. This is a key component in designing a suitable and economy air conditioning. It allows sizing the air conditioning unit, whose role, is to remove heat from the room to the outside.

To perform a heat balance, many elements should be taken into consideration. Must know the surfaces of walls, windows, floors and ceilings of rooms to be air conditioned, which will be multiplied by coefficients to express the result in watts.

Then, the heat balance calculation is used to determine the power of an air conditioning or heating the building principal purpose in maintaining an atmosphere conditions that contribute to the comfort of the individual in his environment [4].

Calculation of heat transfer coefficient of global:

The calculation of heat transfer through a supposed body surface coefficient known transmission (he, hi) and the side dimensions and coefficients of wall material, or of the heat transfer coefficient "U" global depends the constitution of the wall, the inclination of the walls [4, 8-10]. The general equation of the overall coefficient is:

$\frac{1}{U}=\frac{1}{h i}+\frac{1}{h e}+\sum_{i=1}^{n} \frac{e i}{\lambda i}=R$ (1)

Thermal balance in summer (D.T.R C 3-4):

Internal gains:

In addition to the heating system, we must consider the heat gain from the occupation of the building, i.e., the heat generated by the metabolism of people with artificial lighting and the use of devices office, mainly computers [11-13]. These three types of internal gains are calculated separately.

 Gains due to lighting:

Gains lighting contitutes a source of sensible heat. If one knows the installed power for lighting the gains from lighting are given by the following formula:

$G_{e}=\sum P_{n} \times C_{m e} \times C_{c r}$ (2)

Gains due to occupants:

The human body is the seat of endothermic transformations whose intensity varies according to the individual and the activity undertaken. Part of its dissipated in the environment as sensible and latent heat forms:

$\mathrm{G}_{\mathrm{os}}=\mathrm{Nbp} . \mathrm{MS}$ (3)

$\mathrm{G}_{\mathrm{O}_{\mathrm{L}}}=\mathrm{Nbp} \cdot \mathrm{ML}$ (4)

External gains:

Heat gains due to external walls:

The heat gain by the outer walls (wall, roof) are due not only to the difference between the air temperatures lignant their outer and inner faces, but also to the fact that their outer faces are subjected to solar radiation for this there are tables that give the equivalent temperature difference (CLTD) [4].

The heat gain through the walls write:

$\mathrm{Gm}=\mathrm{Um} \cdot \mathrm{Am} \cdot(\mathrm{CLTD})$ (5)

$ (\mathrm{CLTD}) \text { corr }=\mathrm{CLTD}+(25-\mathrm{Tint})+(\mathrm{Text}-29.5)$(6)

Gains due to glass:

Gains due to glazing are the sum of earnings due to the penetration of solar radiation and gains due to the temperature difference.

Gains due to penetration solar radiation:

$\mathrm{Gvr}=\mathrm{Av} . \mathrm{SC} . \mathrm{SHGF} . \mathrm{CLF}$ (7)

Gain due to the difference in temperature:

$\mathrm{G}_{\mathrm{VD}}=\mathrm{UV} \cdot \mathrm{Av} \cdot(\mathrm{Text}-\mathrm{Tint})$ (8)

Gain due to edges:

$\mathrm{Gb}=\mathrm{P.F}(\text { Text }-\mathrm{Tint})$ (9)

Gains by infiltration:

$\mathrm{G} \mathrm{inf}=\mathrm{G} \mathrm{inf}_{\mathrm{s}}+\mathrm{G} \mathrm{inf}_{\mathrm{L}}$ (10)

$\mathrm{G} \text { inf }_{\mathrm{s}}=\operatorname{qinf} . \text { Cpinf }(\mathrm{Text}-\mathrm{Tint})$ (11)

$\mathrm{G} \text { inf }_{\mathrm{L}}=\operatorname{qinf} .(\mathrm{xe}-\mathrm{xi}) . \mathrm{hfg}$ (12)

$\operatorname{qinf}=\frac{N}{3600 \cdot v_{e}} V$ (13)

$\mathrm{N}=\mathrm{a}+\mathrm{b} . \text { wair }+\mathrm{c} |(\mathrm{T} \text { ext }-\mathrm{T} \text { int }) |$ (14)

$\mathrm{Cpinf}=\mathrm{Cpa}+\mathrm{xe} \mathrm{Cpv}$ (15)

4.1 Influence of the type of glass

Glazing plays an important role in the thermal behavior of a building; however its orientation is not overlooked. It is through this reflection that the influence of this parameter was analyzed by considering the non- isolated local studied.

Table 5. Types of glass test

The results will be as follows:

Table 6. Gains due to different types of glass

Type	Uv (w/m². °C)	GVD (w)	GVr (w)	GVTotal(w)	GT (w)
Type 1	5.00	244.80	449.09	693.88	1998.86
Type 2	2.80	137.08	345.08	482.16	1787.14
Type 3	1.10	53.85	387.63	441.48	1746.46
Type 4	0.50	24.48	274.17	298.65	1603.63

 

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Figure 4. Influence de of each type of glazing needs refreshment

It can be seen from Figure 4 that reduced cooling needs when going from type 1 (ordinary glass) type 4 is very sensitive. This decrease is due to the reduction of heat flow through a selective glazing (type 2, 3, and 4) with respect to an ordinary glass (type 1) for the transmission coefficient is low overall heat moving towards types 2, 3, and 4. Thus benefiting from:

Type 2: 211.72 watts which represents 10.6 % of total needs.

Type 3: 252.4 watts which represents 12.6 % of total needs.

For type 4: 395.23 watts representing 19.7 % of total needs.

4.2    Influence of the orientation of glass

It can be seen from Figure 5 that the decrease in heat input when will an east orientation (Window 1: W1) South (window 2: W2) in a direction North West North East is very light. Needs are when the orientation is for the South East and South West 1 window to the second window. This behavior is explained by the fact that the two walls facing south receives a maximum amount of solar energy in summer , while the north is practically no solar gain is the case of the NW- NE, thus optimizing the orientation of windows leads to a tangible reduction in cooling requirements , it is preferable to add still more of a north south glazed window with a smaller surface and contribute to the improvement of natural light in winter and natural ventilation in summer when windows are open. It is found that the orientation of the glazing to the north is obviously the most favorable summer comfort because it is not likely to bring overheating. Note that the difference is not very large, it is around 23 % and this can be explained by the fact that the orientation of the glazing to the south was not really present much of a problem because the sun is at the top of its trajectory and it can be easily protected by a cap or architectural plants masks. The gain value due to the temperature difference remains constant (GVD = 244.8 W) as Av, Uv, Text and Tint keep its values in all cases guidance for both windows (W1 and W2).

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Figure 5. Influence of the orientation of the glazing needs refreshment

4.3    Influence of isolation

The thermal insulation is a key parameter affecting the reduction of energy costs in air-conditioned buildings; the insulation thickness certainly has a significant role on the thermal performance of the building. For this we study the influence of 2 cm, 4 cm and 8 cm insulation (polystyrene, λ = 0.03 W/m.° C) relative to the outer walls of the room they are not studied in isolation.

Thus the coefficient of overall heat transmission exterior wall becomes:

(1).            2 cm: U = 0.75 w/ m².°C.

(2).            4 cm: U = 0.5 w/ m².°C.

(3).            8 cm: U = 0.3 w/ m².°C.

Table 7. Gains due to external walls with insulation

Insulation	Um	Wall South		Wall west		GMTotal(w)	GT (w)
		CLTD	Am	CLTD	Am
Uninsulated	1.50	18.3	10.56	18.4	7.56	498.53	1998.86
Thic =2 cm	0.75	18.3	10.56	18.4	7.56	249.26	1749.60
Thic =4 cm	0.50	18.3	10.56	18.4	7.56	166.18	1666.51
Thic =8 cm	0.30	18.3	10.56	18.4	7.56	99.71	1600.04

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Figure 6. Heat inputs for different outer walls

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Figure 7. Heat inputs for different outer walls

We deduce that local insulation led to a reduction in heat gain in summer, which undoubtedly reduces the cost of cooling.

4.4    Influence of construction materials

The building envelope plays a thermal separation between the inner and outer atmosphere, it acts as a heat storage in the building and as a distributor of the latter to the indoor and outdoor air [11-13], continuing our investigation and we propose to study in detail the thermal behavior of single wall or multi different compositions, to identify those that allow greater energy savings in the case of air conditioning for the Saharan context. For opaque walls, we consider the most used in the building construction sector in Southern Algeria variants. It is noted that the compositions of the initial local external walls are studied most optimal in this case compared to other compositions (Figure 8). The various layers (components) of the outer walls are summarized in the table below:

Table 8. Gains due to various layers of the outer walls

Wall	composition	e (m)	Um (w/m².°C)	GmTotal(w)	GT (w)
1	Raw concrete coated	0.10 0.01	4.10	1362.64	2862.98
2	Coated Cinderblock Coated	0.01 0.15 0.01	2.78	923.93	2424.27
3	Coated Raw concrete Air layer Raw concrete Coated	0.01 0.20 0.05 0.20 0.01	1.71	568.32	2068.66

 

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Figure 8. Heat inputs for different outer walls tested