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A PASSIVE COURTYARD HOME IN JAIPUR, INDIA:

DESIGN ANALYSIS FOR THERMAL COMFORT IN A HOT DESERT CLIMATE

Thulasi Narayan

Arizona State University

Tempe, AZ 85281

[email protected]

ABSTRACT

The success of any architectural design (particularly a

passive system) depends on its ability to deliver thermal

comfort to the inhabitants of the building. Hence it becomes

very important to be able to quantify the improved indoor

comfort conditions. The subject of analysis in this paper is a

design entry that we submitted to the Eco-House Design

Competition 2004 that won a special honorary mention.

The site is situated in Jaipur, India which has a typical

desert climate, hot and dry in the day and cold-dry in the

night. The design solution, a high mass courtyard house

with an integrated cool tower-wind scoop system, was an

architects intuitive response to the site and climate

conditions.

This paper concerns itself with analyzing the performance

of the design, examining the improved quality of thermal

comfort in the indoor living spaces achieved with the high

thermal mass and integrated cool tower wind scoop

configuration. To serve this end, a CFD simulation tool was

selected as the analysis tool.

1. INTRODUCTION

The essence of good architectural design is to achieve not

only spatial delight but more importantly human comfort. Inthe broader arena of sustainable design, passive methods of

achieving human comfort are very important criteria in

working towards the goal of energy conservation. In

addition to being a good architectural space acoustical

standard, adequate level of lighting, thermal requirements

and indoor air quality are all very important criteria for a

successful design.

In desert climates, thermal comfort attains particular prime

importance. Of the various parameters that go into

improving thermal comfort in the desert, natural ventilation

plays a pivotal role. However it is also the most difficult

parameter to measure and control. Natural ventilation in

houses is achieved by a variety of ways, through windows,

courtyards, openings etc. In desert cities, where the harsh

hot and dry climate makes it necessary to have a closed

faade- inward looking courtyard homes, wind towers have

been used over the ages to successfully increase thermal

comfort.

2. THE DESIGN

The climate of Jaipur is extreme with hot, humid summers

and chilly winters. The maximum temperatures during

summer reach a high of 45 Celsius. Winters have sunny

and pleasant days with bitterly cold nights. The temperature

can touch a low of 5 Celsius at night. Fog envelopes the

city during winter evenings. Monsoon starts in the third

week of July, but the city doesnt experience much rain.

The Psychometric chart (Fig 1) shows the ASHRAE

summer and winter comfort zones. The maximum and

minimum temperatures every month fall outside the comfort

zones giving us an indication of the extreme harsh climate.

High air conditioning costs, the rising concern for thedepleting fossil fuels and pollution to the environment from

the production of electricity necessitate the use of passive

cooling measures and natural lighting and ventilation to

achieve thermal comfort.

Based on the analysis of the Bio-climatic charts, fig.2 and

fig.3, the following design strategies were adopted:

1) High thermal mass stone masonry


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2) Natural ventilation Combination of wind scoop and

solar chimney

3) Evaporative Cooling Cool tower with evaporative pads

4) Passive solar heating for selected months louvered

courtyard roof

5) Zoning of night zones activities away from evening sun

exposure.

Fig. 1: Psychometric chart for Jaipur

2. DESIGN EVALUATION

2.1 Tools used for Analysis

CFD is an acronym for Computational Fluid Dynamics. It is

a computational technology that has enabled the real-time

study of the dynamics of things that flow (i.e. heat and fluid

flow). Using this technology the modeled study object is

subjected to the fluid flow and heat transfer physics whichcause the flow dynamics. Repeated complex iterations based

on user specified inputs, on convergence, output the flow

pattern of fluid dynamics.

Fig. 2: Bio-Climatic chart with design strategies -

Maximum Temperatures

Fig. 3: Bio-Climatic chart with design strategies -

Minimum Temperatures

The basis of CFD calculations are the Navier- Stokes

equations derived in the late 1800s by Claude Navier, and

later developed by George Stokes. These equations are very

complicated, too complicated to enable hand calculations.

The great leap in computational technology and processing

power has resulted in the wide use of CFD programs today.

The CFD software used in this study is FloVent produced

by Flomerics ltd.

The field of passive energy design provides a unique

opportunity to use CFD, because of the variables involved.

Till recently the tools used to model and analyze passive

energy systems have been relatively crude, and have not

been equipped to provide a comprehensive thermal comfortanalysis. Since the success of any system (particularly a

passive system) depends on its ability to deliver thermal

comfort to the inhabitants of the building, it is important to

have a simulation tool that allows to model the various

parameters that affect thermal comfort.

2.2. Model Setup in FloVent

The geometry of the residential building (Fig 4&5) is

modeled in FloVent. Thermal mass is provided by Quartzite

stone walls 12 thick and concrete used as the roofing and

flooring material. Table1 gives the properties of the

materials applied in the model.

TABLE 1: MATERIAL PROPERTIES

Material ConductivityBTU/hr.ft.F

Densitylb/ft3

Specific HeatBTU/lbF

Quartzite 1.08 106 0.24

Concrete 0.91 140 0.20

Glass 0.54 1.90 0.38


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The wind scoop-cool tower configuration has been designed

to serve the four daytime zones designated as Living area,

Kitchen area, staircase area, courtyard area. The bedrooms /

night spaces are oriented to the north shielded from

exposure to the late evening sun. The model in FloVent has

been limited to the four-day time zones to decrease

complexity of the model. During certain night runs, the

wind tower setup is completely closed allowing the

opportunity to simultaneously study the behavior of the

model due to only thermal mass.

Fig. 4: Ground floor plan showing the four designated

zones

Fig. 5: Section through the wind scoop-cool tower

configuration and solar chimney

2.2.1 Model parameters

The model was setup as a steady state model within a

boundary solution domain of 100X50X50. The

turbulence type was set to Ke turbulent model. The grid

setting was set to fine, with a maximum size at 7-0. The

fine setting allows dense gridding at the points of interest

with less dense gridding away from the building. This

allows for accurate outputs at the desired points without

greatly affecting the computing time. The ambient

conditions at the edge of the solution domain were set as

110F.

2.2.2 Wind simulation

The wind flow is simulated using the wind generator option

available in FloVents website. The generator comprises of

six small uniform wind sources stacked one above the other

to simulate the increase in wind speed with increase in

height from the ground. For Jaipur, a wind generator option

of 6 km/hr blowing east was found suitable.

2.2.3 Model Run periods

Since the analysis was carried out as a steady state model,

the runs were setup for five study periods capturing the

variation in the annual climatic condition in Jaipur. Tendifferent runs were setup for the same basic model. Fig 7

shows an isometric view of the model in FloVent. Based on

the bio-climatic charts the dampers in the wind tower were

set to completely open/completely closed/partially open for

particular runs.

2.2.4 Physical ModelThe dimensions of the various components of the design

configuration:

1) The wind tower - 6 X 8.75 X 30 high.2) The wind scoop opening - 6 X 7.5 high3) The wind tower outlet opening -3 X 4.5 high4) The solar chimney - 8.5 X 7 X 20 high5) The solar chimney opening to the leeward side

- 5 X 3 high

Fig. 6: FloVent model setup for January 12 -1500 hrs


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Fig. 6: Five selected study periods capturing the variation in annual climate

2.2.5 Evaporative cooling and Night sky radiation

In a cool tower-wind scoop configuration analysis, two main

factors of study would be the evaporative cooling effect due

to air passing over the evaporative pads and the flow

patterns generated in different parts of the model. ThoughFloVent is an excellent tool to model and analyze flow

Patterns; it has no direct capability to model for evaporative

cooling effects. Therefore a negative cooling energy was

assigned to the cooling pad for each run based on the

methodology validated by Vikram Sami (2003). An 80%

resistance was applied to the pads to simulate the resistance

to airflow under the fully open condition. A 60%

evaporation efficiency (capacity of the media to transfer

moisture to the air) of the pads was assumed. Table2 gives

the negative cooling energy and vapor transfer rate used for

the different runs.

TABLE 2: NEGATIVE COOLING ENERGY AND

NIGHT SKY RADIATION

For all runs, the solar radiation option was turned on

(automatically turned off based on the sun position). Fornight runs a night sky radiation value was applied to the

upper face of the solution domain. The night sky radiation

was calculated using the equations:

Ne = 0.787 + (0.864 * loge (Td /273)) (Yellot, 1985)

Tn = Ne0.25 * Ta (ASHRAE, 1978)

Where: Ne = Night sky Emissivity

Td = Dew Point Temperature (in Kelvin)

Ta = Dry bulb temperature (in Kelvin)

Tn = Night sky temperature (in Kelvin)

3. RESULTS AND DISCUSSION

The data from the runs are analyzed separately for each

designated zone. The wind tower faces the dominant wind

direction and the solar chimney with its opening to the

leeward side creates a flowing current through the house.

The high thermal mass creates a shift in the thermal lag.

This can be derived from the MRT being lower than the

outside ambient temperature.

During the summer months in May-June-July, for all the

four zones, the MRT is much lesser than the outdoor peak;

we can see that the thermal mass is keeping the heat out.

The indoor ambient temperature is lower than the outside

ambient by 8-14 C due to the effect of evaporative cooling.

The average wind speeds under fully open dampers for the

living, kitchen, and staircase and courtyard zones are 30

cm/sec, 60 cm/sec, 55 cm/sec and 70 cm/sec respectively.

The courtyard and kitchen areas are directly served by the

wind tower and experience higher wind speeds and greater

thermal comfort. The staircase area is adjacent to the solar

chimney and experiences accelerated exit wind. The

otherwise high operative temperature in the living room due

to the lower wind speed is dampened by the north

orientation.

The combined effect of evaporative cooling, naturalventilation and thermal mass produce a combined drop of 6

to11 C in the peak operative temperature. But the operative

temperature is still outside the comfort zone. Increasing the

wind speed to about 120 cm/sec would bring the operative

temperature into the comfort zone. As Jaipur has a wind

speed ranging from 5.5 km/hr to 7 km/hr only we are forced

to either introduce the use of a ceiling fan to move the


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Chart 1: Showing conditions within the Living Room Zone

Chart 2: Showing conditions within the Courtyard Zone

Chart 3: Showing conditions within the Kitchen Zone

Chart 4: Showing conditions within the Staircase Zone


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operative temperature into the comfort zone or increase the

thermal mass to offset the thermal peak further into the day.

The bio-climatic chart shows passive heating as the required

strategy for night time. Hence the wind-tower was

completely shut down for all five night runs. But in May,

June and July the operative temperature moved above thecomfort zone, showing the need for partial ventilation or

increased thermal mass to shift the thermal peak.

During winter the bioclimatic chart indicates that average

monthly daytime temperatures are already within the

comfort zone. With no need for ventilation as a cooling

strategy in winter the wind tower dampers are completely

closed. In peak winter nights, the operative temperature falls

below the comfort zone by 5C indicating the need for more

thermal mass or can be alternatively compensated for by

electric heating.

The courtyard, the focal space of the architectural design, is

also the most thermally delightful daytime space in the

building - served directly by the wind tower and having no

solar exposure.

4. CONCLUSIONS

CFD is an extremely good tool to study the combined

effects of radiation, ventilation and evaporation on the

indoor thermal comfort. The result trends show that the

design strategies of thermal mass, natural ventilation and

evaporative cooling are good strategies to achieve thermal

comfort in the extreme climate of Jaipur, India. The next

step would be to fine tune the model. The understanding thatthere is an increased requirement for thermal mass to

achieve thermal comfort year round needs to be explored

further. Transient runs for the identified five time periods

would allow us to map the shift in thermal peak. The

thermal lag can then be used to identify the optimum

thermal mass. Adding another layer to the analysis is to

validate the selective passive heating strategy louvered

courtyard roof, achieving a totally passive home for a hot

arid climate in Jaipur, India.

5. ACKNOWLEDGEMENTS

The author would like to express her appreciation to

1) FLOMERICS India Pvt. Ltd for providing theauthor with a student version of the FloVent 5.0

software.

2) Weiran Xu, PhD, Flomerics Inc. for technicalassistance in FloVent modeling.

6. REFERENCES

1. Sami, V. (2003). Modeling thermal comfort deliveredby wind towers using computational fluid dynamics.

Tempe, AZ, Arizona State.

2. Flomerics (2003). Introduction to version 4.1.Southborough, MA, Flomerics Incorporated.

3. American Society of heating, refrigerating and Air-Conditioning Engineers (ASHRAE, 2001), Handbook

of Fundamentals, Atlanta, GA: ASHRAE inc

4. Yellot, J.I. (1982), solar Cooling in Dry Climates.

7. APPENDIX

Figure 1. Section through wind tower showing operative

temperatures July 12, 1500 hrs

Figure 2. Section through solar chimney showing

operative temperatures July 12, 1500 hrs


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