Theoretical Studies Based on Wall Performance

The following papers have studied the energy or temperature performance of different walls and insulation configurations using software simulations. The review shows that the final outcome of the best wall insulation location varies from one paper to another.

E. Kossecka and J. Kosny, (2002) investigated the best location for insulation within a massive wall. The study is based on both mathematical formula and the DOE-2.1E thermal software.

Simulations are done for six different U.S. cities/climates for a one floor ranch plan. Both calculations and software-based methods reached the same conclusion that the best energy conservation for continuously used buildings is placing the massive walls in the interior in order to keep the insulation layer at the exterior. The research observed that the opposite case of having the insulation on the interior will fit better in a non-continuously used building. Looking at the simulated ranch mode, the one floor building has a large pitched attic with no thermo-physical description except for an overall roof value insulation; no details on usage patterns or internal gains are mentioned.

In another paper based on temperature simulation within the Italian city of Florence using ANSYS software, C. Balocco et al. (2008) record surface temperatures of an externally insulated model.

It is not clear if the 3-D model is an actual three-dimensional room, or only a wall. Internal gains are not mentioned. While the study looked at heat flux, the conclusion states that the external insulation will reduce the cooling loads for average (north) latitudes between 40^o-45^o, described as “moderately hot climate with 1821 heating degree days” and with significant solar gains. There is no mention of any performance indicator regarding the percentage of reduced energy or the temperature reduction.

Based on an expanded literature review by O.T. Masoso and L.J. Grobler (2008), the effect of excessive wall insulation is seldom taken into consideration in temperature and energy research.

The authors use what they describe as a well calibrated temperature model. This model includes a wall with middle-insulation. The simulation shows that at a certain point where cooling temperature is fixed, and internal gains are increasing, the energy for cooling will increase.

In another paper by S. Al-Sanea and M.F. Zedan (2011), a mathematical formula was used to calculate the best location and thickness of insulation in Riyadh, Saudi Arabia. Result shows that a double cavity hollow block (2 x 100mm) with three layers of same insulation thickness (3 x 26mm) placed on the outside, inside and in the middle, will considerably reduce energy cooling loads. Within the same city and two of the previous authors: S. Al-Sanea et al. (2012) are looking for the best configuration that combines thermal mass and insulation to reduce cooling loads.

Based on a mathematical model, they found that insulation positioned nearer to the outer surface, combined with a massive wall, will require minimal cooling energy, especially if the building is continuously cooled.

Within the same insulation layering studies, but this time in a theoretical frame work, D.E.M. Bond et al. (2013) reconfirmed the previous statement that three layers of insulation equally distributed within a thermal mass are the best solution for minimal cooling energy loads.

Set in the Italian weather, F. Stazi et al. (2013), start by defining three types of walls: capacity walls (massive one-layer wall); stratification walls (cavity walls); and resistance walls (double

cavity with outer insulation). Later, three dwellings in different areas are chosen, each as one of the described types. The cases are monitored at the same time during both winter and summer.

The paper does not provide any information on how the calibration is done, except that it took into account the actual recorded climate file, the different users and equipment schedules.

Parametric runs that include adding insulation are carried on. Results show that for summer time, stratified or cavity walls tend to have the highest internal temperatures compared to both massive and resistance walls. Whereas, during winter time, resistance walls tend to have higher internal temperature compared to the other two walls. All internal temperatures are below winter comfort within the studied area. The study concludes that adding insulation on a capacity or mass wall at any location (inside or outside) is not good for summer times. Externally added insulations have some positive impact for winters only. As for the stratified or layered wall, the ideal solution is a combination of a ventilated and externally insulated façade for best performance for both winter and summer seasons.

F. Stazi et al. (2015) studied a single-family house of two floors with different construction technics (heavyweight ground floor, lighter weight upper floor) in the Mediterranean climate in central Italy. The study consists of five different new walls with different layout configurations to enhance temperature and energy performance. Hours of overheating, cooling/heating loads and surface temperatures are simulated with the EnergyPlus software during winter and summer.

Software retrofitting shows that summer cooling loads are the least for the as built, whereas the combined minimal cooling and heating is for a vented wall. The latter consists of combination of a massive internal layer with a well-ventilated gap and a high insulated external layer. The gap can be closed during winter time and opened during summer.

Located within the sub-tropical and Mediterranean climate of Valencia, Spain; I. Guillén et al.

(2014) show strong correlation between observed and calculated temperatures. This study is dealing with different types of insulated and ventilated facades during a 24 hours period while the air conditioning system is continuously running. With little solar radiation, the internal temperature followed the variation of the external air temperature. However, when solar radiations became more intense, a large decrease between inside and outside temperature (inside being cooler) was recorded. The study explains that this temperature difference is due to the ventilated multilayer façade where there is an increase of temperature within those layers. Thus, the study concludes that a ventilated layered facade within warm climate would imply consistent reduction of energy without the need to increase the thermal wall mass.

3.5.1 Overview

Within research focusing on walls, conclusions vary between externally located insulation, multiple layers of insulation, and ventilated façade for less cooling and heating energy loads (Table 3.5).

It is worthy to note that none of the papers recommend internally placed insulation.

Table 3.5 Various papers that have dealt based on software studies, with walls, and more specifically location of  insulation for reduced cooling energy loads. 

Authors Year Location Notes Conclusion/Best Location of Insulation

Kossecka, E. and Kosny, J. 2002  6 US cities

climates

External for continuous usage Internal for non-continuous usage

Balocco, C. et al. 2008  Florence; Italy

External

Masoso, O.T. and Grobler, L.J. 2008  Mentions Impact of

Over Insulating Central Al-Sanea, S. and Zedan, M.F. 2011  Riyadh, KSA

3 Layers

2013  Italy Ventilated cavity wall with external insulation Massive wall external or internal insulation is not advised

Guillen, I. et al. 2014  Valencia

Multi-layered ventilated, low mass façade

Stazi, F. et al. 2015  Italy

Ventilated cavity wall with external insulation