Heat Recovery

Most people know about heat recovery in HVAC systems because it helps reduce a building’s energy demand. But, it doesn’t stop there as it comes with many benefits for industrial environments, homes, offices, and many more.

How important is heat recovery in an HVAC system? Heat recovery allows HVAC systems to reduce energy demands for heating and cooling, resulting in lower energy costs for different establishments. Typically, heat recovery systems save about 60% to 95% of the heat in the exhaust air and improve the energy efficiency of homes, offices, and industrial environments.

Learn about heat recovery systems and their importance in an HVAC system in this article. It will also tackle the types of heat recovery systems available today and their unique advantages.

Before you finish reading this post, it aims to help you decide whether heat recovery systems are worthwhile, so make sure to keep up.

Is Installing Heat Recovery In HVAC Systems Worth It?

Yes, installing heat recovery in HVAC systems is worth it. It offers many benefits to your home as it supplies fresh air while retrieving heat that is usually vanished.

This way, it creates a healthier place for you and your family to live in while reducing your heating bills.

For those building a new house, a heat recovery system, also called HRV or MVHR, can help you have a significant amount of savings in terms of heating bills.

It is in contrast with using normal window ventilation and bathroom fans. However, what makes it even more beneficial is that it dramatically improves indoor air quality that boosts the wellbeing and health of dwellers.

To give you a more elaborate explanation of its benefits, here are some of the ways heat recovery in HVAC systems is contributing to homeowners:

Heat Recovery Systems Improves Indoor Air Quality

In the last decade, there is a significant growth in the demand for well-insulated buildings. But to achieve top-notch indoor air quality, well-insulated establishments should also be well ventilated.

Poor indoor air quality can cause a massive impact on damp, condensation, mold, and dust in your home. This can lead to toxic gases buildup, unpleasant smells, and worse, health issues like asthma.

For homeowners who wish to reduce heating costs, ensure that your home has a constant supply of filtered, fresh air. It should also be free from mildew, mold, or condensation, which a heat recovery system can provide.

It Reduces The Heating Cost Of Your Home

Heat recovery in an HVAC system is essential. One of the many reasons is because it can retrieve up to 90% of the heat that is usually wasted and lower your heating needs by up to 25%.

On the other hand, some factors affect its effectiveness. One of those is the airtightness of a building. For instance, a room with a heat exchanger of more than 80% efficiency can only save about 30% of heating loads.

Every day, the cost of a working heat recovery system is at 10p (pence).

Benefits Of Mechanical Ventilation With Heat Recovery (MVHR)

• Your home becomes quieter and draft-free
• Retrieves up to 90% of the usually wasted heat
• Improves the indoor air quality (IAQ)
• Recovers up to 95% of customarily extracted heat
• Reduce your heating costs
• Radon dispersion
• Eliminates mildew, mold and combats condensation
• Removes regular window vents and bathroom fans
• Continuous supply of healthy, fresh, filtered air to your home
• No need for trickle vents or bathroom extractor fans
• Complies with all the latest building control requirements
• A balanced distribution of heat throughout the home
• Fully controllable using remote controls or manual

Heat Recovery Systems: Explained

Heat recovery is the process of retrieving a part of wasted energy through HVAC systems. The Laws of Thermodynamics and inherent inefficiencies in power and heat generating systems limits efficiency across different applications.

For this reason, a high amount of energy ends up being wasted instead of being used in your daily operations and business processes. Heat recovery systems will allow you to allocate a part of this energy for reuse on applications that involve both cooling and heating.

While reading to find out what type of heat recovery systems are ideal for your home, office, or industrial building, you might find out that various technologies already exist for many years.

Heat recovery systems are a practical solution, especially if you are looking for a cost-effective way to reduce the energy cost of a building.

These devices are also a smart choice if you are on a tight budget, concerned about the environment, and overwhelmed by technological advances.

Most industries also operate in integrated and holistic environments to benefit from internal processes to generate energy.

In addition, it allows them to meet their ever-growing operational demands. Manufacturing plants, warehouses, retail stores, office buildings, and other industrial establishments are also similar in common waste heat sources.

The most common prolific waste heat processes are:

• Retrieved and reused waste heat – provides an emission-free substitute for companies instead of costly purchased fuels or electricity.
• Combustion exhausts – Glass-melting furnaces, fume incinerators, cement kilns, aluminum reverberatory furnaces
• Conductive, radiative, and convective losses from heated products – Hot cokes, combustion air preheating
• Cooling water – From furnaces, internal combustion engines, and air compressors
• Boiler process off-gases – Aluminum reverberatory furnaces, steel electric arc furnaces
• Conductive, radiative, and convective losses from equipment – Hall¬Hèroult cells

Types Of Heat Recovery

Rotary Thermal Wheels

If you’re opting for a mechanical way for heat recovery, aim for rotary thermal wheels. In this type of heat recovery, a porous metallic wheel rotates to transfer thermal energy from one airstream to another airstream by alternately passing each fluid.

It works as a thermal storage mass wherein the heat coming from the air is stored temporarily inside the wheel matrix until it is time to transfer to the cooler air stream.

Today, two kinds of rotary thermal wheels, namely enthalpy (desiccant) wheels and heat wheels. These two have geometry similarly, but their differences significantly affect the operation of each type.

Meanwhile, HVAC systems that utilize a desiccant wheel transfer moisture in the airstream with the highest relative humidity to the opposite airstream after flowing down the wheel.

This process can be done vice versa. It is also possible to use the supply air directly or cool the air further, which is an energy-intensive process.

Fixed Plate Heat Exchangers

The most commonly utilized type of heat recovery is the fixed plate heat exchangers. It has been developed for forty years, made with thin metal plates stacked with small spacing plates in between.

Fixed plate heat exchangers are an economical, cost-saving solution than enthalpy wheel designs. It only comprises one moving part, an optional damper assembly, and you can choose from multiple available sizes.

These spaces are where two different airstreams pass through, adjacent to one another. As the temperature shifts through the plate to another airstream, the heat transfer happens.

These devices show an efficacy rate of 90% sensible heat efficiency in transferring sensible heat to another airstream. This excellent rate is due to the high heat transfer coefficients of the used materials, temperature range, and operational pressure.

Heat Pipes

It is a heat recovery device that involves a multi-phase process of transferring heat from airstream to airstream. Heat pipes utilize a condenser and evaporator inside a wicked, sealed pipe to transfer heat and do it through a continuous phase change.

Inside the pipe is a fluid that turns into gas in the evaporator section. It absorbs the thermal energy coming from the warm airstream.

The gas will then turn back into a fluid within the condenser section wherein thermal energy reaches the cooler airstream raising the temperature.

Depending on how the heat pipe is positioned, gravity, wick forces, or pressure helps the gas or fluid travel from one side of the heat pipe to another.

The Advantages Of Heat Pipes For Heat Recovery

1. Long Life

Unlike other types of heat recovery, the components of heat pipes won’t wear out. It is a passive device, which means it has no moving parts. Also, you can order them with a protective coating to protect them from corrosion.

Heat pipes are manufactured to have many charged circuits, and these will unlikely experience leakage under normal operations.

Suppose one of the multitudes of circuits leaks, the impact on the heat pipe’s performance will be very minimal as other circuits would continue working.

2. Passive Operation

Heat pipes do not require energy to operate as they have no moving parts. Instead, it cools and heats refrigerant when two airstreams go across the heat pipes, one on the supply side and the other on the exhaust, changing the two airstreams.

To put it simply, the refrigerant’s phase changes, turning liquid to vapor and vice versa, passing on energy from one side to the other.

3. Isolated Air Streams

Heat recovery heat pipes offer the option to separate the two airstreams using dividing partitions. To prevent cross-contamination, the copper tubes handling the working fluid of the heat pipe are expanded inside the mating holes within the dividing plates to assure an excellent seal.

What makes heat pipes a good solution in laboratory applications is the divider. It is mainly because contamination is a concern in places like laboratories.

4. Flexible Size

Compared to other heat recovery solutions, heat pipes are the minimalist option as they take less space. Aside from that, you can ask for a customized size from manufacturers to fit any application.

Aside from that, heat pipes are also compact in terms of depth. In fact, it is possible to have a six-row heat recovery heat pipe as little as 8 inches.

5. Minimum Maintenance

Heat pipes only require minimal maintenance and the main reason is that it has no moving parts. Therefore, it only needs a periodic cleaning with a coil cleaner like any cooling coil to maintain its efficacy.

Run-Around

This heat recovery option is flexible because it integrates features from other types of heat recovery technology in one. For example, it can recover heat from one airstream then deliver it to another even from a great distance.

A run-around coil heat recovery system comprises at least two coiled heat exchangers connected to a loop through pipes where fluid passes through.

Usually, the fluid is composed of combined antifreeze fluid and water. The brine fluid transfers heat from the hot side through exhaust air or extraction to the cold side (supply air). To recover cooling energy is also possible even during warm days.

A frequency controlling a pump or a three-way valve usually controls the supply heat exchanger’s flow rate. Controlling the flow rate is vital so the supply air’s temperature won’t exceed the preferred value.

Traditionally, the heat exchanger’s size is designed to retrieve about 50% of the heat even when the ambient temperature is 0°C.

Run-around coil systems for heat recovery are regenerative heat recovery systems wherein the airflows are entirely separated from one airstream to another.

This makes it suitable for applications where contamination is not an option, like food industries, hospitals, and pharmaceutical industries. In addition, run-around coil systems are also utilized if extract and supply air units are set up apart due to the layout situation.

Phase Change Materials

Also known as PCMs, Phase Change Materials are a technology used to store latent and sensible heat inside a building structure at a higher storage capacity than standard building materials.

This technology has been extensively studied since it can store heat and transfer cooling and heating demands from conventional peak to off-peak times.

The idea of heat storage through a building’s thermal mass wherein the physical components of the building absorb heat to make the air cooler has been investigated and understood for many years.

Compared to traditional building materials, PCMs have shown that their thermal storage capacity is twelve times greater over the same temperature range.

Meanwhile, there is no reinnovativesearch about the pressure drop across PCMs, so there is nothing to tell about the material’s effect on airstreams.

PCMs, on the other hand, are possible to be directly incorporated into the building structure without affecting the flow like other heat exchanger technologies. Due to this, it can be said that the integration of PCMs in the building fabric does not cause pressure loss.

Where Heat Recovery Systems Work Best

A fully insulated and sealed home or office complex is where heat recovery systems work best.

Since it requires space to completely seal areas where warm air escapes, heat recovery systems are not applicable for old homes that are more susceptible to losing heat than the newer, eco-friendly ones.

Best Place To Position Heat Recovery Unit Inside Your House

Usually, a ventilation system is mounted in places like plant rooms, void spaces, or attics to conceal them. Pipes will be used to feed down to each room to extract state air in exchange for fresh air.

In terms of installation, many heat recovery system providers offer easy to install systems. Some also have an extensive network of trusted installers around the country you’re at.

Among the main features of heat recovery and ventilation systems is that you can easily control the ventilation inside your building.

Heat Recovery Systems On An Industrial Scale

Heat recovery systems are also applied on an industrial scale. They collect the heat escaping from large boilers, wherein the heat is removed through a flue.

This technology exists in most new condensing boilers, but the older ones might be more suitable to use a flue economizer.

Smart Heat Recovery

Nowadays, heat recovery systems also integrate innovative capabilities that reduce extracted heat during the summer season.

As a result, establishments such as offices and residential spaces maintain the desired level of comfort.

In addition, these smart capabilities can also be utilized to eliminate more heat from wet rooms or busy kitchens where the temperature is typically higher than other rooms.

The Environmental Impacts Of Heat Recovery Systems

One of the problems linked to protecting the global environment and fossil fuel consumption is energy saving. Due to the ever-increasing cost of energy and the worsening of global warming, improved energy systems are in high demand.

Better energy systems will allow better energy efficiency, reducing energy consumption and lower greenhouse gas emissions.

To reduce energy demand, the ideal solution is to utilize energy in the most efficient way possible. Waste heat recovery is rising in popularity in the past years as it improves energy efficiency.

In many countries, around 26% of industrial energy, like hot fluid or gas, is still wasted. But in the past twenty years, people are becoming more interested in recovering waste heat from different industries to optimize the systems being used to retrieve heat from waste gases.

As a result, these efforts are improved, which reduces global warming and energy demand around the world.

Energy Consumption

HVAC, in most industrialized countries, contributes one-third of the overall energy consumption. Dehumidifying and cooling fresh ventilation air make up 20% to 40% of HVAC’s overall energy load in humid and hot climatic regions.

But, these numbers can be higher in places where 100% fresh air ventilation is needed. It means that a higher amount of energy is required to meet the occupants’ requirements.

Heat recovery is becoming a necessity because of the increasing cost of energy for new air treatment. Initially, heat recovery systems were designed to reduce the energy consumption of an establishment for heating, cooling, and ventilation by retrieving the waste heat.

So, this system can be incorporated in commercial or residential buildings as stand-alone or combined units to save energy. Lower energy consumption also helps to lower greenhouse gas emissions for a better and more sustainable world.

Greenhouse Gases

A massive contributor to climate change is carbon dioxide, along with nitrous oxide and methane. It is the reason why the greenhouse gas emissions are usually represented as CO2 equivalent emissions.

From 2000 to 2005, there was an increase in global greenhouse gas emissions at around 12.7%. In most developed countries, around 30% of greenhouse gas emissions are produced by buildings every year.

Another study also says that establishments in European Union countries contribute about 50% of the CO2 emissions.

However, if proper actions are executed, reducing these alarming greenhouse gas emissions by around 70% is possible than the levels assumed in 2030.

Global warming is the effect of the increased greenhouse gas emissions caused by the high energy demand. Due to this, reducing gas emissions became one of the most crucial issues of the world that should be resolved immediately.

With the help of heat recovery systems, reducing greenhouse gas emissions can be possible by mitigating the energy needed to heat and cool establishments.

As proof, research initiated by the Scotch Whisky Association at Glenmorangie distillery found that 175t of CO2 a year will be conserved within a year of payback period.

Another report says that 10MW of retrieved heat can be used to conserve €350,000 per year in emission cost.

Meanwhile, the UK Climate Change Act of 2008 targets to reduce around 34% in greenhouse gas emissions by 2020 and 80% by 2050. Aside from that, they highlighted the importance and potential of heat recovery technologies to attain this goal.

Conclusion

To conclude, heat recovery in an HVAC system is essential as it helps to reduce energy demand, resulting in more significant energy savings and reduced greenhouse gas emissions.

In addition, the use of this technology can benefit homeowners, different industries, and the world because of its excellent performance. Since most types of heat recovery systems are also wear-proof, your initial investment will definitely pay off.