February 2012 | Air Conditioner Cost Saving from Well-Insulated Dwelling

Abstract. Air conditioning is the largest electricity consumer in a house, so how to achieve maximum air quality healthy and comfortable with minimum air-conditioning energy consumption should be considered. Air conditioning energy efficiency can be achieved primarily from the design of the building. In this article the building uses b-panel®. b-panel® is a double layer of reinforced concrete panel which is specially designed with a layer of expanded polystyrene insulation (EPS) in the middle. Figure 1 illustrates a house made of b-panel®.Factors that affect the cooling load in the room are the altitude, solar radiation, the orientation of the location of the building which affects the absorption of radiation, the color on the walls of buildings, and other supporting material quality (like the glass in the window). Therefore, the saving that occurs for the cooling load in the highlands (Bandung) and the coastal areas (Jakarta) will be different. This article presents the analysis of this difference.


Figure 1 – House with b-panel® system

Indonesia is a humid tropical country. This conduces that many regions in Indonesia have to use air conditioning to obtain thermal comfort because it is not enough if the building uses only natural ventilation. Negative characteristics in humid tropical climate which cause unreliable natural ventilation for thermal comfort are:

  • Highly dependent on climate and air quality. There is no clear time difference between rainy and dry season, it can even have overlapping.
  • The temperature is not easily predictable. Temperature in Indonesia is relatively high with little day-night amplitude (24oC – 32oC) and high solar radiation, which is greater than 900 W/m2.
  • The wind speed is not easily predictable. Wind speed is low in the morning and evening, while the wind blows stronger at noon.
  • The humidity is not easily managed. High humidity (60% – 95%) causes the sweat does not evaporate, so the skin feels sticky and uncomfortable.
  • Others. Dusty air quality, odor, and pollution. In addition, there are presence of insects and environmental disturbances (e.g. noise) which are difficult to prevent.

Therefore, in order to obtain thermal comfort in the room is to use artificial ventilation, such as air-conditioning (A / C). The advantages of using A/C are:

  • The temperature was cooled and adjusted easily.
  • The velocity and direction of air movement can be designed. (0,6 m/s < V < 1,5 m/s)
  • The humidity can be lowered into the comfort zone(40% < Relative Humidity (RH)< 60%). The humidity in the wet tropics gives the largest contribution of thermal comfort.
  • Cleanliness and health of air can be maintained with the filter and ionizer to kill bacteria, fungi, and others which can provide a fresh effect.
  • Due to most of the use of A/C in a closed room, the side benefits are obtained, namely acoustic comfort andodor management.

However, there are some losses caused by the use of A/C. Among these are:

  • Wasteful of energy. Electrical energy which is used achieves an average 40% of the total use of a dwelling.
  • The tendency of an enclosed space causes pollutant that accumulates inside, causing sick building syndrome. Therefore, artificial ventilation is required with adequate ACH (Air Change per Hour). (Source: Sistem Kelengkapan Bangunan, Ir. Paulus A.S., MT.)

The main task of the use of A/C is to carry the heat from the room to the outdoors. Therefore, the heat that comes into the room or that arises in the space should be as little as possible.One way to reduce the incoming heat is to use building materials that can withstand ambient temperature and solar load entering the room as much as possible (having a low transmittance value), such as using a expanded polystyrene(EPS) insulation. b-panel® is a double layer of reinforced concrete panel which is specially designed with a layer of EPS insulation (EPS) in the middle.The use of  b-panel® in building can block the propagation of heat from the outdoor. This will impact positively to the reduction of energy consumption A/C, so that residents can save money on electricity cost.
Here is a diagram of the components of heat into the room and the heat generated in the room. These components are required to calculate the required cooling load in the room. Furthermore, it is used to determine the A/C model used with adequate cooling capacity of A/C.


Figure 2 – Heat components (Source: www.egydown.com)

In this article saving A/C which occurs if the b-panel® is used as a building material in the highland (Bandung) and the coastal area (Jakarta) will be discussed. Here are data from the city of Bandung thermal comfort:

  • The afternoon temperature is 28oC–29oC. Even in Tegallega and Gedebage heat island has been formed with a minimum temperature of 27oC. Afternoon temperaturein a state of extreme reaches more than 30oC. Nighttime temperature is 16oC–19oC. Thus, the daytime temperature has exceeded the threshold of comfort 26oC.
  • Relative humidity (RH) which is 80%-90% has exceeded the threshold of comfort 60%.
  • Wind speed and direction are uncertain. In an open environment wind speedcan reach 2–4 m/s (Source: Sistem Kelengkapan Bangunan, Ir. Paulus A.S., MT.)

Here are the thermal comfort fatcs of Jakarta:

  • The average afternoon temperature in 2010 is between31,3oC–34,3oC.The average night time temperature is between 24,2oC–25,5oC (Source:World Meteorological Organization).
  • In 2005 the average RH in the dry season is 60%-85%, whereas the average RH in wet season is 79%-88%.
  • In 2005 the wind speed in the dry season reaches 0.2 to 0.8 m/s, while the wind speed in the wet season is from 0.6 to 1.6 m/s. Wind leads to the south and southeast. (Source: Studi Ekologi Kualitas Udara di Jakarta, Tangerang, dan Bogor)

For ease of analysis, the limits of the room to calculate the cooling load will be made. Cooling load is calculated for each building using b-panel® and red brick in Jakarta and Bandung.There is a house with a length = 8 m, width = 8 m, and height = 3.2 m with 4 room where three rooms is fitted with A/C and 1 room is not is fitted with A/C. All rooms are identical and have a window (see Figure 3 and Figure 4).


Figure 3 – House front view


Figure 4 – House plan

Wall have a thickness of 15 cm. Each room has two walls in direct contact with the outside air. Room A and room C has a wall associated with the air in the room without A/C, while the B room has 2 walls associated with the air in the room is fitted with A / C (which means no thermal flow). This house uses roof deck. Two types of wall are analyzed:

  1. Wall made of traditional brick, 11 cm thickness, plastered and finished both surfaces, each thickness is 2cm(Uwall = 2,55 W/m2 C, αwall = 0,89). Table of value of the absorption of solar radiation to the outer walls and an opaque roof (a) are indicated in Table 1:
  2. Walls made of reinforced concrete which center is filled the center with expanded polystyrene (EPS) is known as the b-panel®. Regarded as lightweight concrete walls. EPS is 9 cm thick and the thickness of concrete to each side is 3 cm (Uwall = 0,4 W/m2 C, αwall = 0,86).

Table 1 – Absorption of solar radiation values for external walls and opaque roofa
(sumber: www.jurnalinsinyurmesin.com)

Outer walls and roof deck were painted with medium yellow color αpaint = 0,58. If the outside walls were painted with different color, it will give the different absorption of solar radiation value (α), as shown in Table 2 below:

Table 2 – Absorption of solar radiation values for the paint on the surface of the outer wall
(Source : www.jurnalinsinyurmesin.com)

On the walls glass windows were fitted with the glass length = 0.9 m and the glass height = 1.5 m (Uglass = 4,48 W/m2 oC, from the factory brochure). The average incidence angle of the sun coming through the walls and windows are assumed ß = 75o and the window has a Φ = 0.75.
These other data along with a brief explanation are required for cooling load calculation if the building is planned in two different cities, namely Jakarta and Bandung:

  1. Solar radiation. Solar radiation is radiant energy derived from thermonuclear processes occurring in the sun. Solar radiation energy is in the form of light and electromagnetic wave. The spectrum of solar radiation itself consists of two, namely, short-wave ray and long-wave ray. This includes short-wave rays are x-ray, gamma ray, ultraviolet ray, while the long-wave ray is infrared ray. The total amount of radiation received at the earth’s surface depends on four factors:
    • The distance of the sun. Any change in the distance of the earth and the sun cause variations in the acceptance of solar energy.
    • The intensity of solar radiation is the size of the angle of incidence of sunlight on the earth’s surface. The amount received is directly proportional to the magnitude of the angle of incidence angle.Ray with an oblique incidence angle gives less energy in the earth’s surface caused by the energy spread on the surface area and also because the ray has to travel a further layer of the atmosphere than if the light with a perpendicular angle.
    • Sun duration is the distance and duration between sunrise and sunset. Due to the fact that Bandung and Jakarta are located in the southern hemisphere, and then the length of the day will be greater at the end of the year (December/January) compared to the middle of the year (June/July).
    • Influence of the atmosphere. Rays through the atmosphere will be partially absorbed by gases, dust, and water vapor, reflected back, emitted, and the remainder forwarded to the earth’s surface.(Source: www.wikipedia.com)

    The following is a table of data measurement result of solar radiation intensity across Indonesia by BPPT and BMKG from 1965 to 1995.

    Table 3 – The intensity of solar radiation in Indonesia

    Source: ‘Analisis Potensi Pembangkit Listrik Tenaga Surya di Indonesia’
    By Irawan Rahardjo and Ira Fitriana

    Known average solar radiation = I = 1000 W/m2. This is the average solar radiation power in Indonesia.

    1. Outer Air Layer Transmittance. fo= 20 W/m2 oC
    2. Air Change Hour (ACH). ACH is the number of how many times the change of air in a certain space (usually in the room or house).Change of the air in a confined space is very important for several reasons, mainly because we need fresh air to live.Without the exchange of fresh air, the moisture will be trapped in a building, mold and allergens can grow, as well excessively hazardous gases (such as carbon monoxide, carbon dioxide, and urea-formaldehyde) can remain in the house.The stale air is not good for health. Because humans and animals receive that air into the body when breathing, sweating, washing, bathing or drying, we need ventilation to increase the number of air changes in the home with fresh outdoor air.With the new focus on energy efficiency to reduce carbon and reduce dependence on fossil fuels, consumers are trying to seal their homes from the transfer of air in and out in the winter and summer.The importance of fresh air intake cannot be ruled out. Air exchange does not represent the process of exchanging all air in the room or structure unless it can be considered as plug flow.The actual percentage of indoor air having been exchanged in a given period depends on the efficiency of air flow from the room and what methods are used in that ventilation process. The actual amount of air exchange in a well ventilated scenario is 63.2% after 1 hour and 1 ACH. To achieve an appropriate balance of pressure, the amount of air in and out of the surface should be the same.
    3. Table 4 – Air change rate
      (Source: www.wikipedia.com)

      Ventilation = 3 ACH (Air Change Hour)

      1. Temperature in the room mounted A/C is conditioned = T1 = 20oC (in a state of balance, there is no heat flow in the dividing wall with another room).
      2. Here are the Bandung and Jakarta climate datameasured by BMKG on 5 Januari 2012.

      Table 5 – Climate data in Bandung (Source: www.bmkg.co.id)

      Table 6 – Climate data in Jakarta (Source: www.bmkg.co.id)

      1. 6. Each room contains a single occupant, and uses two CFL (Compact Fluorescent Lamp) with the power of 11 Watt. Each person releases 140 Watt of heat.

      The following is analysis of cooling load calculation that are required in both places. Calculation is derived from the dictates of Buildings Completed Systems Subjects prepared by Ir. Paulus A. S., MT. The figure below shows that heat into the room.


      Figure 5 – Diagram of source of heat into the room

      Cooling load calculation of the red-brick building in the coastal area (Jakarta):
      The formula used is Qm = Qi + Qs + Qc + Qv . . Heat that need to transfer: heat inside room + solar heat penetrated glass/window + heat outside penetrated wall + heat from outside. Here are the calculations for room A and room C.
      Calculate first Δglass and Δdinding :

      Δ Tglass
      = T0 – T1
      = 28,50C – 200C
      = 8,50C

      Δ Twall by calculating the average absorption of plastered and coated brick:

      a
      = 0,5 (αwall + αpaint)
      = 0,5 (0,89 + 0,58)
      = 0,735

      Wall surface temperature outside

      Ts
      = T0+ (I.a.cosß/f0)
      = 28,5 + (1000)(0,735)(cos75/20)
      = 38,010C

      Thus Δ Tdinding = 38,01 – 20 = 18,010C

      Cooling Load:

      Qi
      = total heat (humans and equipment)
      = lamp heat + human heat
      = (2)(11) + (1)(140)
      = 162 W

      Qs
      = solar heat that penetrated the glass
      = αglass .I . ?
      = (0,9)(1,5)(1000)(0,75)
      = 1012,5 W

      Qc
      = heat through the wall and roof deck + heat through the glass
      = αwall .Uwall . ΔTwall + αglass .Uglass.ΔTglass
      = [(2 x 4 x 3,2 – 1,5 x 0,9 + 4 x 4)(2,55)(38,01 - 20) + (4 x 3,2)(2,55)(26 - 20)] + (1,5 x 0,9)(4,48)(28,5 – 20)
      = 2095,91 W

      Qv
      V
      = heat due to ventilation
      = (space volume) x (ACH)/3600 seconds
      = (4 x 4 x 3,2) x (3)/3600
      = 0,0427
      = 1300.V. ΔT
      = (1300)(0,0427)(28,5-20)
      = 471,84 W

      Qm= 162 + 2095,91 + 471,84 = 3742,25 W. Thus, the heat that must be transported out of the room A and room C is respectively 3742,25 W. In the same way, the required cooling load to room B is:
      Qi = 162 W
      Qs = 1012,5 W
      Qc = 1900,07 W
      Qv = 471,84 W
      Qm = 162 + 1012,5 + 1900,07 + 471,84 = 3546,41 W. The heat that must be transported out of the room B is 3,55 kW. Thus, the cooling load required for this house is = 3742,25 W + 3742,25 W + 3546,41 W = 11030,91 W = 11,03 kW.

      Cooling load calculation of the b-panel® ® building in the coastal area (Jakarta):
      Here is the calculation for room A and room C:
      Qi = 162 W
      Qs = 1012,5 W
      Qc = 368,99 W
      Qv = 471,84 W
      Qm = 162 + 1012,5 + 368,99 + 471,84 = 2015,33 W. Thus, the heat that must be transported out of the room A and room C is respectively 2015,33 W. In the same way, the required cooling load to room B is:
      Qi = 162 W
      Qs = 1012,5 W
      Qc = 338,27 W
      Qv = 471,84 W
      Qm = 162 + 1012,5 + 338,27 + 471,84 = 1984,61 W. The heat thatmust be transported out of the room B is 1984,61 W. Thus, the cooling load required for this house is = 2015,33 W + 2015,33 W + 1984,61 W = 6015,27 W = 6,02 kW.

      Cooling load calculation of the red-brick building in the highland (Bandung):
      Here is the calculation for room A and room C:
      Qi = 162 W
      Qs = 1012,5 W
      Qc = 1530,61 W
      Qv = 249,80 W
      Qm = 162 + 1012,5 + 1530,61 + 249,80 = 2954,91 W. Thus, the heat that must be transported out of the room A and room C is respectively 2954,91 W. In the same way, the required cooling load to room B is:
      Qi = 162 W
      Qs = 1012,5 W
      Qc = 1465,33 W
      Qv = 249,80 W
      Qm = 162 + 1012,5 + 1465,33 + 249,80 = 2889,63 W.The heat thatmust be transported out of the room B is 2889,63 W. Thus, the cooling load required for this house is = 2954,91 W + 2954,91 W + 2889,63 W = 8799,45 W = 8,80 kW.

      Cooling load calculation of the b-panel® building in the highland (Bandung):
      Here is the calculation for room A and room C:
      Qi = 162 W
      Qs = 1012,5 W
      Qc = 259,92 W
      Qv = 249,80 W
      Qm = 162 + 1012,5 + 259,92 + 249,80 = 1684,22 W. Thus, the heat that must be transported out of the room A and room C is respectively 1684,22 W. In the same way, the required cooling load to room B is:
      Qi = 162 W
      Qs = 1012,5 W
      Qc = 249,68 W
      Qv = 249,80 W
      Qm = 162 + 1012,5 + 249,68 + 249,80 = 1673,98 W. The heat thatmust be transported out of the room B is 1673,98 W. Thus, the cooling load required for this house is = 1684,22 W + 1684,22 W + 1673,98 W = 5042,42 = 5,04 kW.

      Table 7 – Required cooling load

      By using the b-panel®cooling load can be reduced by 45,5% in Jakarta and by 42,7% in Bandung to the building with red brick. Below is a comparison chart of the required cooling load between Bandung and Jakarta.


      Figure 6 – Cooling load chart in Bandung and Jakarta

      Conclusion. The use of b-panel® consistently and significantly lowers cooling load more than 40% in both coastal areas (Jakarta) and the highlands (Bandung). The average temperature differences in the two cities cause different A/C load. However, drastic improvement of A/C power consumption occurs when the entire surfaces of the walls and roof deck in direct contact with the outside wrapped with a layer of insulation, such as the presence of EPS in the b-panel® system.

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