Energy Efficient Hospital Patient Room Design: Effect of Room Shape on Window-to-Wall Ratio in a Desert Climate

Abstract

This paper reports on a research that utilized simulation techniques for identifying the most efficient hospital patient room designs and their associated window-to-wall ratios. Simulation of the energy consumption and daylighting performance of common patient room designs were conducted using a range of Window-to-Wall Ratios (WWRs). The paper focuses on arriving at solutions that balance between the reduction of energy consumption and the achievement of proper daylight distribution in the desert climate of Cairo, Egypt. Simulations were conducted using the Diva-for-Rhino, a plug-in for Rhinoceros modelling software to interface with the Energy Plus, Radiance and Daysim software. Results demonstrated that solar penetration is a critical concern affecting patient room design and window configuration in desert locations. Use of the outboard bathroom patient room design was found to be the least efficient among the tested alternatives. Although it has a smaller external wall size, it failed to provide energy consumption that is lower than that of the other options. Its best energy performance was 20% higher than that of the nested bathroom patient room design. However, the outboard bathroom design allowed for larger WWRs (70%-90%), which might prove useful for external view exposure purposes. The nested and inboard bathroom patient room designs provided better energy performance. However, this was on the expense of window size. The acceptable cases of these designs had smaller WWRs, (30%-40%). The results of this paper demonstrated the need for the careful consideration of the size of windows and openings in relation to different patient room designs. Simulation techniques can prove useful in this regard.

Full text

Energy Efficient Hospital Patient Room
Design: Effect of Room Shape on Window-
to-Wall Ratio in a Desert Climate
Ahmed Sherif
Hanan Sabry
Rasha Arafa
Ayman Wagdy
[Department of
Construction
and Architectural
Engineering, The American
University, Cairo, Egypt]
[Department of
Architecture, Faculty of
Engineering Ain Shams
University, Cairo, Egypt]
[Department of
Construction
and Architectural
Engineering, The American
University, Cairo, Egypt]
[Department of
Construction
and Architectural
Engineering, The American
University, Cairo, Egypt]
ABSTRACT
This paper reports on a research that utilized simulation techniques for identifying the most efficient
hospital patient room designs and their associated window-to-wall ratios. Simulation of the energy
consumption and daylighting performance of common patient room designs were conducted using a
range of Window-to-Wall Ratios (WWRs). The paper focuses on arriving at solutions that balance
between the reduction of energy consumption and the achievement of proper daylight distribution in the
desert climate of Cairo, Egypt. Simulations were conducted using the Diva-for-Rhino, a plug-in for
Rhinoceros modelling software to interface with the Energy Plus, Radiance and Daysim software.
Results demonstrated that solar penetration is a critical concern affecting patient room design and
window configuration in desert locations. Use of the outboard bathroom patient room design was found
to be the least efficient among the tested alternatives. Although it has a smaller external wall size, it
failed to provide energy consumption that is lower than that of the other options. Its best energy
performance was 20% higher than that of the nested bathroom patient room design. However, the
outboard bathroom design allowed for larger WWRs (70%-90%), which might prove useful for external
view exposure purposes. The nested and inboard bathroom patient room designs provided better energy
performance. However, this was on the expense of window size. The acceptable cases of these designs
had smaller WWRs, (30%-40%). The results of this paper demonstrated the need for the careful
consideration of the size of windows and openings in relation to different patient room designs.
Simulation techniques can prove useful in this regard.
INTRODUCTION
Hospitals are typically considered one the most energy demanding building types. Patient rooms
compose the largest volume of hospital buildings. The external walls of patient rooms represent the most
significant part of the external surface area of these buildings. Windows can contribute significantly to
the healing process and reduction of pain and length of stay in hospitals through the provision of
daylight and allowance of external view (FGI, 2010). However, they can also contribute negatively to
the energy consumption of these buildings, especially in desert climates, where the cooling load
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represents a significant percentage of total energy consumption.
Sizing the windows of patient rooms should be carefully considered in relation to patient room
shape. Some common patient room designs have a small external wall surface area with a large room
depth, while others have larger external room surfaces and a reduced depth of the work area. The
windows of patient rooms should minimize solar penetration, reduce overheating; yet at the same time
maximize daylighting and patient access to external view. The objective is to reduce the total energy
load while maintaining comfort and quality health care.
Literature addressed the effect of environmental aspects on healthcare delivery. Ulrich
recommended that natural light improvement could help reduce stress and fatigue, while increasing
effectiveness in delivering care, patient safety and overall healthcare quality (Ulrich, 1991 and Ulrich et
al., 2004). In an attempt to develop patient room designs to create healing environments, the effect of
natural daylight on the patients’ average length of stay in hospitals was investigated. Studied factors
were patient’s average length of stay as an index of health outcome, and the differences in environment
during daylight hours, such as illuminance, luminance ratio, and illuminance variation in the hospitals
patient rooms (Choi et al., 2012).
In research work more relate to this study, energy efficient building envelope treatments were
examined for a generic reference hospital in Thailand. Parametric analysis was conducted. The overall
thermal transfer value, glazing material, Window-to-Wall ratio (WWR) and external shading devices
were addressed. The annual energy savings due to increasing daylighting reached up to 15.4% and
11.3% for the electrochromic and green tinted glazing respectively (Chungloo et al., 2001).
Optimization of window opening in a hospital patient room was addressed in a research that aimed
at providing daylighting, external view, while minimizing the energy consumption. An optimization
methodology was demonstrated through parametric computer simulations to determine the optimum
window design in the form of window width, sill and lintel heights and shading device depth (Shikder et
al., 2010). The impact of using various window shading systems and different window glazing types on
the energy consumption of a typical hospital Intensive Care Unit room space in Egypt was examined. It
was found that energy savings reaching up to 30% could be achieved by the use of externally perforated
solar screens and overhangs positioned at a shading angle of 45° (Sherif et al., 2013-a).
In another study, daylighting performance was simulated for a typical hospital Intensive Care Unit
room space located in Cairo, Egypt. Several window configurations were simulated in the four main
orientations, where the effect of adding shading and daylighting systems was examined. Successful
window configurations were recommended for different window to wall ratios (Sherif et al., 2013-b).
The above review of literature demonstrates that a limited number of publications addressed with
the relationship between hospital patient room designs and the associated window configurations.
Research work concerned with this relationship in desert environments is almost nonexistent.
Configuring the windows of patient rooms for energy efficiency, while providing acceptable daylighting
levels, could pave the way for reaching more sustainable hospital designs.
OBJECTIVE
This paper aimed to compare the energy consumption and daylighting performance of common
hospital patient room designs. Investigation focused on the design of windows facing the south
orientation under the desert clear-sky of Cairo, Egypt. The larger aim was to arrive at satisfactory patient
room designs that minimize energy consumption and maximize the utilization of daylighting, thus help
improve the delivery of sustainable healthcare facilities.
METHODOLOGY
The methodology was divided into two consecutive stages. Stage one investigated the energy
performance of the tested patient room design cases along with the alternative window configurations.
Stage two concentrated on the analysis of daylighting adequacy for the cases which achieved acceptable
performance in stage one. Three of the most common patient room designs were selected for
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investigation. These were: Design A: the outboard bathroom patient room design; Design B: the nested
bathroom patient room design; and Design C: the inboard bathroom patient room design. The tested
rooms were assumed to have a similar floor area (22 m²). The layout, dimensions and parameters of the
tested rooms are shown in Table 1 and Figure 1.
Table 1. Parameters of the Tested Patient Room.
Internal Surfaces Materials
Walls
Reflectance
50% (Medium Colored Internal-walls Off-White)
Ceiling
Reflectance
80.0% (White Colored Ceiling)
Floor
Reflectance
20.0% (generic floor)
Window Parameters
Glazing Double glazing clear (VT=80 %)
Sun Breaker
Reflectance
35.0% (Outside Facade)
Figure 1 The tested patient room designs
Seventeen window size values, expressed as Window-to-Wall Ratios (WWRs) were analyzed for
each patient room design. The values ranged from 10% to 90%, at 5% increments. The shape and
location of the tested windows alongside the external wall of the patient room space are illustrated in
Figure 2. A horizontal sun breaker was assumed to be positioned on top to the window. Its overhang
value provided a sun protection angle of 45°, as shown in Figure 3. This angle was based on the results
of previous research work (Sherif et al., 2013 b).
Figure 2 The shape and position of the tested window on the external wall at different WWRs.
Simulations were conducted using the climatic data of the city of Cairo, Egypt (30°6'N, 31°24'E,
alt.75 m) that enjoys a year-round desert clear-sky. The city is characterized by a hot-arid desert climate,
Design C:
The Inboard Bathroom
Design A:
The Outboard Bathroom
Design B:
The Nested Bathroom
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according to Köppen-Geiger (2006). The tested patient rooms were assumed to be located on the second
floor level of a hospital building, where windows were assumed to face no external obstruction. The
external ground surface was assumed to have a 20% reflectance value. Grasshopper which is a plugin for
Rhinoceros modeling software and a parametric modeling tool was used to automate the energy and
daylighting simulation process. By activating this function, the Grasshopper plugin generated a
parametric model for each WWR and ran a climate based analysis through DIVA interface. Energy
simulation was conducted using the EnergyPlus software. Daylight simulation was conducted using the
Radiance and DAYSIM software. The Diva-for-Rhino plugin for the Rhinoceros modeling software was
used as an interface.
Figure 3 The overhang of the shading device protecting the tested window.
Methodology of Stage One: Energy Consumption Analysis
The aim of this phase was to investigate the energy consumptions associated with the three tested
patient room designs (cases A, B and C). The annual energy consumption resulting from the different
WWRs of each patient room design was calculated. The cooling, heating and lighting energy
consumption values were accounted for. The WWRs which resulted low energy consumption values
falling within 3% from the lowest value for a certain patient room design were considered acceptable
cases for such as design.
Energy simulation parameters were selected to focus on studying the performance associated with
room shape and window configuration. The effect of thermal transmittance through walls and ceiling
from the adjacent spaces was neutralized. Thus, the thermal transmittance from all walls and ceiling,
except that of the window wall, were set to be adiabatic. The effect of the adjacent rooms was considered
to be of no relevance to the thermal performance sought in this comparative study. The building was
assumed to be fully air conditioned and minimal thermal transmittance was expected from the other
internal spaces that would have identical set conditions. The external wall was defined as a 0.35 m thick
double brick insulated cavity wall with a U- value of 0.475 W/m² –k that carried the tested window at its
center. The air conditioning system heating and cooling set points were assumed to be 22°C/26°C
respectively. The occupancy time of the studied patient room was chosen to be all day, at a rate of 10 m²/
occupant. The hourly lighting schedules that were generated through the annual Daylight Availability
analysis by the Radiance and DAYSIM software were used as basis for artificial lighting energy
calculations. This artificial lighting was set to be dynamically controlled by sensors according to
daylighting adequacy.
Methodology of Stage Two: Daylight Availability Analysis
The aim of this stage was to evaluate the year-round daylighting performance of the cases that
proved successful for each of the three design configurations in stage one. Simulation parameters used in
investigations were: ambient bounces = 6; ambient divisions = 1000. The occupied time of the patient
room was assumed to be from 06:30 AM to 10:30 PM. In this study, the reference plane on which
daylighting performance was simulated was the patient bed level plane (0.90 m height). The spacing of
the analysis grid was set at 0.7m * 0.7m. Four points were placed on the patient bed. The reference plane
contained 46, 54 and 53 measuring points in each of the three tested patient room designs A, B and C
respectively, as shown in Figure 1. The illuminance value was assumed to be 300 Lx (IESNA, 2000).
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Three Daylight Availability evaluation levels were used (Reinhart & Wienold, 2011). First, the “daylit”
areas were those areas that received sufficient daylight at least half of the year-round occupied time.
Second, the “partially daylit” areas were those areas that did not receive sufficient daylight at least half
of the year-round occupied time. Third, the “over lit” areas were those areas that received an oversupply
of daylight, where 10 times the target illuminance was reached for at least 5% of the year-round
occupied time. Two daylighting acceptance criteria had to be satisfied. First, 100% of the patient bed
surface area should be “daylit”. Second, at least 50% of the patient room area should be “daylit”.
SIMULATION RESULTS
Results of Stage One: Energy Performance
The total annual energy consumption values expressed in Kwh/m² were calculated. The results are
as shown in Table 2. It summarizes the energy consumption results in the south orientation at different
WWRs for the three investigated room designs A, B and C. The cases that achieved the required
threshold were highlighted with a light tone in the table.
Table 2. Total Annual Energy Consumption for Layout Designs A, B and C
Annual Energy Consumption (Kwh/m2)
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
WWR%
176
175
174
175
173
176
176
177
177
178
177
182
184
186
189
192
180
Design A
183
180
177
174
171
167
162
158
154
150
147
147
147
151
153
168
169
Design B
183
180
178
177
174
169
163
161
160
158
155
151
154
158
166
175
173
Design C
Use of design B that has a nested bathroom resulted in the lowest energy consumption among all
three room design types. The consumption was as low as 147Kwh/m2 in WWRs 30%-40%. Moreover,
design C (inboard bathroom design) achieved a very close value of 151 Kwh/m2 in WWR 35%. Use of
these designs resulted in a better performance in comparison with Design A (outboard bathroom design)
which failed to produce a value lower than 177 Kwh/m2. Furthermore, use of Design A resulted in the
highest energy consumption among all alternatives. It reached 192 Kwh/m2 at 15% WWR. On the other
hand, its consumption was lower than the other two alternatives at high WWR values. Using a 90%
WWR with designs A and B resulted in comparatively larger energy consumption values, reaching up to
183Kwh/m2.
On the other hand, the outboard bathroom design configuration (Design A) achieved larger window
sizes and larger number of options in comparison with the other two layout configurations. The
acceptable WWR range of Design A extended from 40 to 90%. Fewer acceptable WWR choices and
smaller window sizes were identified for the nested bathroom configuration (Design B). These ranged
from 20% to 45% WWR. A very limited range of WWRs was found acceptable in the inboard bathroom
configuration (Design C), where only three WWR cases (30 to 40% WWR) met the required criterion. In
design A, the bathroom location on the outboard wall reduced the size of the exposed external wall
surface, thus reducing the thermal exposure of the patient's room to the hot desert climate. However, this
was overcome by the increased artificial lighting energy load, as explained later. This was not the case in
the nested and inboard designs, where the size of the external wall surface was much larger.
To explain the behavior described above, the lighting, cooling and heating consumption values
were analyzed. As expected for a desert environment, cooling represented the highest values, followed
by lighting electricity then heating loads, which were almost negligible as shown in Figures 4, 5 and 6.
The performance of design A is shown in Figure 4. The lighting electricity load significantly
decreased with the increase of WWR. This could be attributed to the increase of daylighting use, which
resulted in a reduction of artificial lighting. However, the nature of the patient room plan type resulted in
overall higher levels of artificial lighting, with subsequent high cooling energy. On the other hand, the
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cooling energy loads slightly increased with the increase of WWR. This allowed the acceptance of larger
WWRs, reaching up to 90%. The use of an outboard toilet with the resultant small external wall surface
dampened the effect of changing the WWR. This was observed in the gentle curve slope of the cooling
energy consumption for WWRs 20%-90% that it is almost flat.
Figure 4 Design A annual cooling, heating, lighting and total energy loads for different WWRs.
The performance of Design B is shown in Figure 5.The lighting electricity load decreased at a
constant rate with the increase of WWR, while the cooling energy loads increased considerably with the
increase of window to wall ratio (WWR). This is observed in the considerable increase and the curve
slope of the cooling and the total energy use from 40% to 90% WWR. This could be attributed to the
design of this patient room type that has a nested toilet that is associated with a larger external wall
surface. This increased solar exposure and allowed the window transmitted solar energy.
Figure 5 Design B annual cooling, heating, lighting and total energy loads for different WWRs.
The energy consumption of patient room Design C is shown in Figure 6. This design was found to
produce behavior almost similar to that of Design B. Both share a large exposed external wall. It was
noticed, thought that the cooling energy of design C was slightly higher than that of Design B. This
could be attributed to the cooling load resulting from the slightly increased lighting electricity.
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Figure 6 Design C annual cooling, heating, lighting and total energy loads for different WWRs.
Results of Stage Two: Daylight Availability Analysis
In this stage, the cases that achieved successful energy performance in stage one were evaluated for
daylighting adequacy. Results are shown in Table 3. In Design A, acceptable daylight availability was
only achieved at large WWRs. Only 5 of the tested cases passed the daylight availability test in this case.
On the other hand in Design B, 4 of the 5 tested cases resulted in acceptable daylighting performance. In
Design C, all of the three tested cases resulted in an acceptable daylighting performance.
Table 3. Percentage of “Daylit” Area Relative to Patient's Room and Bed Plane Areas
For more detailed discussion, eleven cases were analyzed for the outboard bathroom design
(Design A). Simulation results revealed that the amount of acceptable “daylit” areas was directly
proportional to the increase of WWRs values. Only large windows achieved adequacy in the case of the
outboard bathroom design. For WWRs between 70% and 90%, the “daylit” area reached 72% of the
space area, especially at 85% WWR. The “partially daylit” areas dominated the patient room, where it
reached 50% of the space in average (40% to 65%). However, it decreased gradually until it became
unnoticeable at 85% WWR (15% of the space). In contrast, the “overlit” area was almost constant (13%
as an average) in the tested WWRs.
On the other hand, when the bathroom was located in-between two adjacent patient rooms (Design
B: The nested bathroom), only four cases from five energy efficient ones achieved adequacy (30% to
45% WWRs). The “Daylit” area reached 80% of the space, at a WWR value of 45%. Although, the
“daylit” area of the patient bed plane achieved adequacy in the 25% WWR case, it was unacceptable in
relation to the overall patient room area testing (41% “daylit” area). The “Partially daylit” area decreased
gradually until it almost disappeared (1%), in the case of 40% WWR.
For the inboard bathroom design (Design C), the three energy efficient cases (30%, 35% and
40%WWRs) were acceptable for daylighting performance. The “daylit” area values for the patient room
space were almost similar (60% at an average). For the three design configurations, the "over lit" area
percentages did not exceed 15% in average for overall the patient room space in all accepted daylight
availability cases.
25 30 35 40 45 50 55 60 65 70 75 80 85 90
Room
26 28 35 39 43 48 54 61 63 72 70
Bed
0 25 100 100 100 100 100 100 100 100 100
Room 41 54 57 65 80
Bed
100 100 100 100 100
Room 60 58 62
Bed
100 100 100
WWR %
Design A
Design B
Design C
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CONCLUSION
The energy and daylighting performance of three common patient room designs were simulated.
The performance resulting from use of a range of window sizes (expressed as Window-to-Wall Ratios -
WWRs) under the clear-sky desert sun of Cairo, Egypt was examined for each of these room designs.
Table 4 summarizes the range of WWRs that were recommended for each patient room design for
satisfying the energy and daylighting criteria. In addition, the balanced WWRs that satisfy both energy
and daylighting criteria at the same time were identified.
Results of this study demonstrated that solar penetration is a critical concern affecting patient room
design and window configuration in desert locations, like in Cairo, Egypt. Use of the outboard patient
room design was found to be the least efficient among alternatives. Although it has a smaller external
wall size in comparison with the other alternatives, it failed to provide an energy consumption that was
lower than that of other two tested room designs. Its best energy performance was 20% higher than that
of the nested bathroom design. This could be attributed to the increase of artificial lighting that resulted
from allocating the bathroom along the external façade in the outboard bathroom design. However, the
outboard design allowed for larger WWR values. This might prove useful for external view exposure
purposes. Although the nested bathroom and inboard bathroom designs provided better energy
performance, this was on the expense of window size. The acceptable cases of these designs had smaller
WWRs, between 30% and 40%.
The results of this paper demonstrated the need for a careful consideration of the size of windows
and openings in relation to different patient room designs. Simulation Techniques proved useful in
identifying the wiNdow configurations that satisfy both the energy and daylighting requirements at the
same time.
Table 4: Recommended WWRs for Patient Room Designs A, B and C
Patient Room Designs
Design A
Design B
Design C
Energy
40% - 90%
30% - 45%
30% - 40%
Daylighting
70% - 90%
30% - 90%
30% - 90%
Balance
70% - 90%
30% - 45%
30% - 40%
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30th INTERNATIONAL PLEA CONFERENCE 1
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