Japan’s “green curtains” can reduce your air-conditioner usage

Due to the heat island effect and global warming, Japanese summer continues to get hotter and hotter every year. Moreover, around the world, household electricity bills continue to skyrocket. Is there any way to cool the house without relying so much on air conditioning?

In Japan, “green curtains” are gaining popularity as sunshades. Green curtains, as the name suggests, are a way to block out the sun by growing plants outside the window. Commonly grown are vines such as bitter gourd, loofah and morning glory. This is not only aesthetically pleasing to the eye but also of great benefit as it can cut down the power bill and carbon emissions.

Benefits of Green Curtains

Keep the room cool by blocking out the sunlight.
The many thick leaves block direct sunlight from entering through the windows, thus reducing the rise in indoor temperature. The curtains have a shielding effect that cuts about 80% of the heat energy of sunlight. In addition, it helps alleviate the heat island effect by preventing heat from accumulating on building walls and other surfaces.

Moisture evaporating from leaves lowers ambient temperatures.
Water absorbed by plants from their roots evaporates from their leaves, removing heat from the surrounding area. The water vapor in the leaves evaporates, which removes heat from the surrounding area. And the cool breeze drawn into the room saves energy by reducing the use of air conditioners and other cooling devices.

Enjoy a vegetable garden even with limited space.
In addition to relieving the heat, you can also enjoy growing and harvesting plants. Bitter gourd and green beans with vines can be enjoyed for their flowers, and the harvested fruits can be cooked. Green curtains can be installed even on small balconies like those in urban areas in Japan.

How much money can I save on electricity for air conditioning?

In 1985, Chubu Electric Power Company (Chubu Electric Power Co., Inc.) conducted an experiment to demonstrate the energy-saving effects of green curtains.

In the following experiment, two identical buildings were analyzed, one with a green curtain and the other in direct sunlight. In the experiment, both buildings were cooled at 28°C between 8:00 and 11:00 a.m., and the power consumption of the air conditioners was measured and compared. In the building with a green curtain, the power saving rate exceeded 20% for all six days of the experiment, demonstrating an average power saving effect of 30%.

In 2019, Tokyo City University reported the result of their experiment on green curtains. They examined the thermal mitigation effect of the green curtain in the condominium for 48 days by analyzing the indoor and balcony temperatures both in households with and without green curtains. The study concluded that the balcony globe temperature of the households with green curtains was 0.6°C lower than that of those without green curtains during air-conditioner usage. Moreover, the air-conditioner usage time of the apartments with green curtains resulted in 40% less than those without green curtains.

Surrounded by lush greenery, your mind will be soothed, and the gentle breeze will feel more pleasant than usual. Many types of plants for green curtains are easy to grow, even for beginners, so they require surprisingly little effort. If you are interested in lowering your electricity bill and gardening, growing green curtains may be a worthwhile experience this summer.