In an era where energy savings and sustainability are in focus, heat recovery plays a crucial role in optimizing energy consumption. By utilizing heat that has already been produced, we can reduce the need for additional energy, lowering both costs and environmental impact. This makes efficient heat recovery an attractive solution.
Heat recovery is a process that enables the reuse of heat or energy from a process or system that would otherwise be lost. Typically, this involves transferring heat from outgoing air to incoming air that needs to be heated. This process can be applied in various contexts and contributes to improved energy efficiency by reducing overall energy consumption.
One of the most common applications of heat recovery is in ventilation systems. In modern buildings, ensuring good ventilation is essential for maintaining a healthy indoor climate, but ventilation can also lead to significant heat loss, especially during the winter months. This is where heat recovery comes into play.
Ventilation systems with heat recovery work by capturing the heat from used indoor air before it is expelled into the environment. This heat is then transferred to the incoming fresh air, preheating it without requiring additional energy. This process reduces the need for supplementary heating and can significantly lower a building’s energy consumption.
Heat recovery is a process that can be implemented in many ways, depending on the needs of a particular building or industry. Below, we explore some of the methods used at Unic Air:
Heat exchangers are a core component of many heat recovery systems and come in several types, each with its own advantages:
Rotary Heat Exchanger: The rotary heat exchanger, consisting of a rotating wheel made of corrugated aluminum, creates small channels for airflow. It transfers humidity from the exhaust air to the supply air, making it ideal for indoor climates in offices. It maintains high thermal efficiency and prevents icing by controlling the wheel’s rotation speed.
Counterflow Heat Exchanger: The counterflow heat exchanger is a plate exchanger made of aluminum plates that effectively separates airflows by allowing them to cross each other. With a horizontal central section, it provides higher heat recovery than the crossflow exchanger but requires automatic defrosting due to the risk of icing.
Crossflow Heat Exchanger: The crossflow heat exchanger is also a plate exchanger made of aluminum plates that separates airflows by crossing them. While its efficiency is lower compared to the counterflow and rotary exchangers, it allows condensate to drain and is easy to clean.
Glass Tube Heat Exchanger: Found in our GX units, this exchanger uses small intersecting glass tubes that separate airflows and prevent odor transfer. It features a built-in automatic washing system that removes grease and dirt from the exchanger daily, ensuring optimal performance.
Run-around Coil Heat Exchanger: This exchanger uses two liquid-coupled coils—one in the exhaust airflow to extract heat and another in the supply airflow to receive heat. There is no direct contact between airflows, preventing contamination.
Recirculation is an efficient way to reuse heat by circulating air multiple times through the system. At Unic Air, we have developed a ventilation unit with double recirculation and integrated cooling, allowing for demand-controlled ventilation. The unit can switch between double recirculation and fresh air operation depending on air quality.
Double recirculation enables the reuse of already cooled or heated air, unlike traditional ventilation units that rely solely on 100% fresh air. The unit does not compromise air quality, as it is designed to switch to fresh air operation if air quality reaches a predefined threshold for CO₂ or humidity.
Heat recovery from exhaust air
Unic Air has also developed a ventilation unit for restaurants equipped with a glass tube heat exchanger and a patented automatic washing system. This system efficiently recovers heat from greasy exhaust air. The ventilation unit operates without filters in the exhaust section, allowing greasy air to pass directly through the glass tube exchanger, where a significant portion of the heat is recovered and transferred to the supply air. This recovered heat is often lost in traditional systems due to the challenges posed by greasy air.
Heat recovery is an effective way to optimize energy consumption, offering both economic and environmental benefits. At the same time, it’s important to consider the challenges and barriers that may arise when implementing heat recovery systems.
Common Heat Recovery with Heat Exchangers:
By installing heat exchangers in ventilation systems, the warm air already heated can be used to preheat the incoming air. This reduces the need for additional heating, resulting in lower energy costs. Over time, these savings can quickly offset the investment in a heat exchanger.
Recovery Through Recirculation:
With a ventilation unit capable of alternating between recirculation and fresh air operation based on air quality, significant energy savings can be achieved in heating, cooling, and fan operation. At Unic Air, we have seen cases where double recirculation has led to energy savings of over 50% compared to traditional ventilation units.
Heat Recovery from Exhaust Air:
In Unic Air’s ventilation units designed for restaurants, there is a short payback period due to their efficiency. In practice, these units have eliminated the need for additional heating to warm the supply air. This results in significant energy cost savings, with many cases showing operational savings of up to 40,000–60,000 DKK annually. This makes the payback period for the ventilation unit exceptionally short.
Heat recovery not only offers economic savings but also significantly reduces environmental impact:
Reduction in Heat Consumption and CO₂ Emissions
Without heat recovery, there would be an increased reliance on external heat sources, such as district heating, leading to higher CO₂ emissions. By recovering heat from existing processes, the need for additional heat production is minimized, promoting more eco-friendly energy use and reducing the strain on the environment.
Efficient Use of Resources
Maximizing the use of heat that has already been produced reduces energy resource waste. This is critical for lowering the overall environmental footprint and fostering a more sustainable future.
While heat recovery has many advantages, there are also challenges and barriers that must be addressed:
Drying of Indoor Air
A potential issue with heat recovery systems, particularly in ventilation, is the risk of drying out indoor air. This can occur if the recovered air lacks sufficient humidity, which may result in an uncomfortable indoor climate.
Maintenance and Cleaning of Heat Exchangers
In environments such as kitchens, where there is a high risk of grease buildup in exhaust air, maintaining heat exchangers is a critical factor. Unic Air’s glass tube heat exchangers with automatic washing systems provide an effective solution to this problem, ensuring optimal performance and reducing maintenance challenges.
Heat recovery is a process where heat energy that would otherwise be lost is reused to heat fresh air or water. It works by transferring heat from outgoing airflows to incoming air through a heat exchanger. This reduces the need for additional heating and improves energy efficiency.
Heat recovery can be achieved using various heat exchangers such as rotary heat exchangers, counterflow heat exchangers, crossflow heat exchangers, and glass tube heat exchangers. Each type offers unique advantages depending on the building's needs. Additionally, heat recovery can be optimized through recirculation, where air is reused multiple times to maximize energy savings.
Heat recovery offers both economic and environmental benefits. Economically, it reduces energy consumption by reusing existing heat, leading to significant savings on energy bills. Environmentally, it decreases the need for additional heat production, reducing CO₂ emissions and making buildings more sustainable.
Implementing heat recovery in a building requires the installation of appropriate heat exchangers and ventilation systems. The process involves selecting the right type of heat recovery technology suited to the building's size and needs, as well as ensuring proper integration with existing heating and ventilation systems. Professional advice and installation are often necessary to ensure optimal performance and energy efficiency.
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