Keep your building cool with night flushing

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Night flushing, also known as night cooling or night ventilation, is a critical component to enhance the performance of naturally ventilated buildings that are used during the hot summertime. It works by harnessing the cooler temperatures of the night to reduce reliance on energy-intensive cooling systems. This is better for the environment and can help reduce energy usage. However, with increasingly hot weather impacting countries around the globe, the importance of night flushing extends beyond energy efficiency – it can also have a positive effect on our health. Without the capability to cool buildings during the night, indoor temperatures can remain unreasonably high, leading to e.g. heat exhaustion and decreased productivity. Implementing night flushing within our ventilation strategies can mitigate these risks by ensuring buildings remain cool and comfortable. In this guide, we delve deeper into the concept, how it can be implemented, the benefits, and how WindowMaster's solutions can help you achieve night flushing within your architectural designs.

Discover how night flushing is possible in your building

With decades of experience under our belt, our approachable team can guide you on integrating night flushing into your building. Contact us today to learn how night flushing can help you stay cool and enhance your building's comfort and efficiency.

What is night flushing?

Night flushing is a passive cooling strategy that taps into the natural drop in temperature after sunset to expel accumulated heat within a building's thermal mass. During the day, buildings absorb heat from occupants, equipment, and sunlight, which can lead to overheating - an issue that is becoming increasingly common, as we’ve seen with the recent heatwaves across the world. Night flushing systems counteract this by opening parts of the building envelope, such as windows or vents, to allow cool night air to circulate and remove stored heat.


How does night flushing work?

Night flushing can be implemented through various ventilation strategies, depending on your design and needs. For structures with natural ventilation, automated window openings facilitate cool air flow.

This is made possible through WindowMaster’s highly efficient actuators, which mechanically open and closes windows at specific times. They can be connected to a control system that manages their operation, based on factors including temperature, humidity, and air quality.

Learn more about our actuators

Warm air can also be expelled through other openings such as ducts to aid the night cooling process. Mixed-mode ventilation combines these approaches, making it easier to cool rooms at night.

Why do buildings need night flushing?

Modern buildings are increasingly becoming airtight and often use materials that promote insulation. While this is good in the winter months when it’s much colder, the trapped internal heat can lead to discomfort in the summer, when temperatures begin to climb. It’s an issue likely to get worse, as summer temperatures persistently surpass heat records. Night flushing offers a natural cooling solution, reducing the reliance on air conditioning systems to ensure indoor environments remain comfortable, all year round. As it’s a low-energy solution, it can also reduce energy spend, saving businesses money. We explain this in more detail in our whitepaper.

Download whitepaper on night flushing
Night Cooling

How to enhance the effects of night flushing

To make the most of natural cooling at night, it’s important to use building materials that can absorb and release heat effectively (these are materials with high thermal mass). Ensuring these materials are exposed to the outside air so they can exchange heat will also assist in night flushing. Additionally, adding solar shades that mitigate daytime heat gain can enhance its effectiveness. This will help keep the building cooler, so there’s less warm air to ‘flush’ at night.


Key benefits of night flushing

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    Health and well-being

    In the face of rising temperatures, night flushing is an effective means of lowering the temperature, making the building more comfortable and healthier for its users

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    Smart cooling

    It can reduce the daytime use of mechanical cooling systems, which can be costly to run and maintain

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    Powering up ESG

    By lowering overall energy usage, night flushing can help support businesses in their ESG goals

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    Boost your building

    It’s possible to improve the effectiveness and efficiency of the building envelope. The building envelope refers to the outer shell of a building, including walls, windows, doors, roofs, and insulation. These improvements can deliver increased comfort for occupants, reduced energy consumption, and improved overall building durability and longevity.

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    Breathe easy

    The systematic opening and closing of windows ensures fresh air enters the room, improving oxygen levels for greater mental clarity

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    Cooling with care

    Reducing energy consumption is better for the environment, making it a farsighted choice

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In which climates is night flushing most effective?

Night flushing's efficiency depends on a building’s thermal properties and local climate conditions. It's particularly effective in climates with noticeable day-to-night temperature swings, though it can provide benefits even in warmer climates by facilitating airflow and reducing airborne pollutants.

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Common concerns with night flushing

Security concerns during night flushing are addressed by strategic window placements and intelligent actuators programmed with safety functions. WindowMaster's solutions include wind and rain sensors to automatically close windows in adverse conditions, ensuring both security and efficiency. They are also typically placed on the higher levels of a building, where access is extremely difficult and use specific window shapes e.g. windows that aren’t too tall or long.

Read how we handle the common concerns
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How does WindowMaster technology assist in night flushing?

WindowMaster has allocated numerous resources to designing control systems that offer flexibility and control for its users. This includes both NV Advance® and our cloud-based system NV Embedded® that offers the ultimate in customisable control

Sensors send data on the indoor and outdoor conditions allowing the system to calculate an optimized night cooling approach while maintaining building security. Additionally, NV Embedded® can also be linked directly to building management systems (BMS). This means that rooms are constantly monitored, allowing them to open and close windows systemically to ensure effective night flushing.

Are night flushing systems easy to maintain?

Night-flushing capable natural ventilation systems are easy to maintain. As it’s a simpler system when compared with traditional air conditioning units, it requires less maintenance. The beauty is in its simplicity. With fewer parts, problems are less likely to arise. It’s merely a case of keeping hinges or small components well-greased, which can be done every few years.

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“Night flushing is now becoming increasingly important as we see summer temperatures rise, causing buildings to become uncomfortably warm. For building owners who want to ensure optimal indoor comfort for years to come, having night flushing capabilities can definitely have a positive effect on their overall ventilation strategy. WindowMaster's technology makes it possible to harness the night's cool breeze, providing a natural way to remove unwanted heat. Through our simple but high-tech solutions, businesses can elevate their building's performance whilst providing a healthy environment for staff and visitors.”
Kasper Ravn

Kasper Højmark Ravn

Building Performance Engineer


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