Integrating passive cooling in urban masterplanning & building design. Part 1：an engineering example for a residential community in hot-humid climate

1. Introduction

There are a lot of discussions on how to integrate passive cooling into planning and design, and how to evaluate the real impact on the benefits by introducing such kinds of technologies, e.g. natural ventilation, shading facilities and indoor/outdoor thermal comfort.

I would like to share my experiences on the relevant topics of passive cooling design and climate adaptive design. I will try to publish a series of articles to illustrate how we implemented these considerations especially in hot humid climate. Most of the work in these articles were comleted when I was still working as a chief engineer and team lead in the State Key Lab of Subtropical Building Science in China until 2017, while some of the following up-scaling work are still continuing after I joined @UNEP Copenhagen Climate Center (UNEP CCC). Some of the academic research work in these articles were financed by the National Natural Science Foundation of China and Asian-Pacific Energy Partnership through NREL, USA.

In the article, I would like to introduce what kind of integration work has been done during the urban planning and detailed design stage to integrate passive cooling in a high-density residential community in the city of Guangzhou, China.

As shown in the above figure, it guides the design strategies for residential buildings to ensure indoor thermal comfort in Guangzhou under TMY data and recommends some of the general solutions in urban planning and architectural design.

However, these recommendations need to be tailored according to different conditions of projects. After all, there are no fit-all solutions.

2. The site

The project is a residential community located in Guangzhou. It has 57,000 sq. meters of land and 220,000 sq. meters of built-up buildings. The main function of the buildings is residential apartments with 100 to 130 sq. meters for 10 high-raising residential buildings, and several service buildings including a kindergarten, service centers and a primary school, as well as small shops on the ground floor.

The project was planned and designed in 2005-2006, and completed in construction in 2008. The project was ranked best selling residential community in 2009. And we kept measuring the outdoor and indoor environment from 2010 to 2013 after it was occupied, as well as the electricity consumption on building level in the same period. Through optimization in master planning and architectural design, it was voted as one of the best residential communities for living in south China in 2015 and 2016.

3. The challenge

The land for the project is mainly facing east-west, as shown below. The big challenge is how to prevent the big sunshine in the summer while keeping the same built-up areas. Meanwhile, since the summer in Guangzhou is very hot and humid, it is crucial on how to use suitable natural ventilation, shading, and shadows from building and landscaping to cool down both the external and internal environment.

At the same time, it is required by the design standard to keep living rooms and bedrooms sufficient sunshine in winter, to control the winter external wind speed under 1.2m/h around the primary school and the kindergarten.

Thus, the challenges for the master planners are:

1) How to locate the 10 high-raising residential buildings as a balance among apartment amount, outdoor/indoor comfort and cooling saving?

2) Where to locate the primary school and the kindergarten regarding higher requirements for thermal/wind safety and comfort?

The challenges for the architects are:

1) How to design the shape of buildings to provide potential and additional shading in summer while sufficient sunshine hours in winter?

2) How to make natural ventilation both indoor and outdoor possible in summer while assuring the winter wind velocity in the safe range?

3. Passive cooling for master planning

In order to overcome the challenges in master planning, the large scale of simulations are conducted to facilitate master planner to allocate the buildings. As a result of integrated building cluster (for 10 buildings in total) performance simulation, the best solution is to put the buildings in 'S' shape, which gives a lot of self-shading from the buildings themselves and enable the comfort level outdoor ventilation in summer.

3.1 Outdoor shading and facade sunshine simulation

Building cluster simulation for shading and facade sunshine

The simulation of outdoor sunshine hours in winter, as shown below, shows the best locations for the primary school and kindergarten (point 1 and 2), which requires at least 3 hours of sunshine per day.

The simulation of outdoor sunshine hours in summer, as shown below, requires additional shading in the pedestrian level in some regions (dark green and yellow). Thus, the urban planners need to think about the potential landscaping solutions. Especially for point 1 and 2, where the primary school and kindergarten locates.

Above two figures show the simulation results in summer and the landscaping and outdoor shading facilities under urban planning as in reality.

3.2 Enabling nature ventilation

Suitable outdoor nature ventilation in summer can bring in benefits of better outdoor thermal comfort and high potential for indoor nature ventilation so as to save cooling energy consumption. The detailed simulation of outdoor environment in summer can give more detailed recommendations to the urban planners on where to locate the primary schools and kindergarten, as well as outdoor spaces for resting and playgrounds, as shown in the two figures below.

At the same time, the results of wind environment simulation in winter gives recommendations on how to protect the primary school and the kindergarten from high wind speed regarding wind safety, as shown in the two figures below.

The blue regions highlighted in the figure above shows the low winter wind speed, which is good for both primary school and kindergarten.

P.S. The above figures are actually cartons that can show wind direction and speed at different heights of the buildings. However, when uploading to LinkedIn, all of them are failed to show.

4. Passive cooling for architectural design

Normally, passive cooling in architectural design also includes the design of the building envelopes, e.g. U-values of roof, wall and windows, and SHGC for windows, and min efficiency for cooling equipment etc.. However, all these have been regulated by the building energy efficiency codes in Guangzhou. Thus, in this article, I don't mention the process for these MEPs, but focus more on how to enhance natural ventilation and control sunshine hours in the floor plan design of residential apartments.

4.1 External shading design for apartment spaces in summer and winter

The detailed simulation of sunshine hours and time for each space in the apartment can give architects recommendations on which spaces need external shading facilities and how to set up shading facilities (vertical, horizontal, hybrid or operable), as shown below.

One of the benefits of arranging the building cluster in 'S' shape is to provide self shading for east and west facades in summer so as to reduce the size of shading facilities for some apartments, while in winter still providing suffient of sunshine hours (min 4 hours per day) for these apartments. And this has been considered a cost-effective way to reduce cooling demand in summer in the region.

4.2 Architectural design for nature ventilation

Even though the wind speed is high enough in the outdoor environment, it is necessary to have the floor plan design properly to make indoor ventilation possible. The architects should consider the arrangement of different spaces that require more ventilation compared to others, like to arrange bedrooms and living rooms as the first priority for ventilation instead of kitchens and toilets. Meanwhile, they also need to decide where to put the windows and how big they should be, whether they should be fixed or operatable. All these need to have a detailed simulation, and the building performance modelling expert needs to work closely with the architects and do the simulation several times in order to find the best solution.

Above two figures give examples for the most optimized floor plans as the final design. The aim is to reduce as much as possible the area with dark blue, which indicates low or even no wind at all. As you can see from the figures, sometime it is very difficult to ensure all the spaces in the building to have good natural ventilation, especially for the spaces in the back side of the main wind direction, like the spaces D in both cases. In that case, we need to go for mechanical ventilation, e.g. fans or split AC.

5. Conclusions and recommendations

As shown in the above sections, it is possible to achieve both thermal safety and comfort through passive cooling design. But it requires to combine the efforts in upfront stages of master planning, and continue to implement with landscaping design and architectural design. The integration of passive cooling technologies can provide residential buildings a cost-effective solutions to reduce the cooling demand from the building and the community. If combined with suitable envelope performance (MEPs), it can achieve higher overall cooling saving in the buildings. However, only urban planners or architects can not achieve the target. Normally, designers with different background need to work as a team, together with building performance modellers.

In the next articles, I will continue to share about low-cost cooling design for social housing, thermal comfort evaluation in micro climate of residential communities, and the impacts of micro climate on building energy consumption.