Night purge ventilation: A sustainable, secure solution

When it comes to sustainability in construction and architecture, passive design is becoming an increasingly critical and present force.

A building with a good passive sustainable design takes the forces of nature that occur onsite — free, renewable, naturally occuring, and thus, passive — and uses them to perform functions that would otherwise rely on traditional electricity supply.

Sunlight beaming into solar panels is a well known example. But it’s not just electricity generation that can be achieved through this method. If employed properly, sustainable passive design can reduce temperature fluctuations, improve indoor air quality and make a space drier and more comfortable to be in.

Night cooling systems can tick these boxes and more. Also known as night purge ventilation, it utilises the principles of natural ventilation — whether wind driven or thermal buoyancy — to allow warm stale air to be exhausted and the building mass to be cooled.

When evening temperatures drop, the building envelope is opened, allowing for the cool air to enter the building and dissipate the stored heat via convection.

But how exactly does this work, and what kinds of buildings should take advantage of it? Peter Millard, the technical services director for EllisCo, says that as buildings become better insulated due to higher building standards, the need for night time cooling is becoming increasingly necessary even at outdoor temperatures below 0°C.

Night cooling strategies are often used in education buildings, office buildings and industrial buildings that are not occupied at night. They are especially effective in those with exposed surfaces that readily absorb heat such as concrete falls or walls.

“When buildings like this are occupied during the day, there are many different things that emit heat: heat pumps, machinery, people,” says Peter. “So the idea is to use the cooler night temperatures to flush out all the stale, warm air — so that when people come in the morning, the building’s air is refreshed.”

Passive cooling can be achieved naturally by opening windows or vents — but it’s not quite as simple as that. After the windows are opened, wind-driven or thermal buoyancy-driven airflow can then cool the space.

Correct placement of windows and openings during the design of the building will allow maximum benefits — enabling good air paths for cool air to enter and exhaust the building.

But to ensure that this is handled properly, Peter recommends a proper natural ventilation solution that can offer feedback about window opening position, or that provides window status, directly to a building management system. This will help maintain the security and integrity of the building without compromising on the benefits of night cooling.

WindowMaster, a Danish company specialising in sustainable ventilation and facade solutions, offers several products that can help facilitate this system of night purging. And as the sole distributor of WindowMaster’s products in New Zealand, EllisCo has considerable expertise in the area.

“The night purge system usually involves windows or louvres being automatically opened for a set period overnight, allowing a natural air flow through the building,” says Peter. “And it’s not like an HVAC system or a fan — you’re using the principles of natural ventilation.

“So cool air enters windows at low level and stale warm air rises and flows out of windows at high levels – clerestory windows, skylights or louvres for example. And it’s as simple as having a window management system that intuitively opens and closes windows at the right times.”

The potential for not only sustainability but also reduced costs is considerable, Peter says. A night purging system reduces the need for the HVAC system to be activated as soon as the building is occupied in the morning.

Then there are the health benefits of a good quality ventilation system: airborne pollutants are more likely to be flushed out — an increasingly valuable attribute in an era of a global pandemic.

And since the system uses WindowMaster intelligent actuators in combination with an intelligent control system, users are able to control the openings very precisely — as the windows normally do not have to open fully during night purging to secure an effective cooling keeping the building secure. During the day when occupied, windows can be fully opened.

“This kind of system has a sustainability factor, but it also provides buildings with a healthier internal environment,” says Peter.

“And with the technology that comes with the system, security is another added benefit.”

Learn more about EllisCo and its offerings.