Author: Mycond Technical Department
Humidity control systems are an integral part of building engineering solutions, yet their impact on the overall carbon footprint often goes unnoticed. This leads to significant errors when assessing the environmental performance of buildings and equipment. A correct understanding of thermodynamic fundamentals and engineering methods not only enables accurate estimation of CO₂ emissions but also allows optimization of dehumidification systems to minimize their environmental impact.
The thermodynamic nature of CO₂ emissions in dehumidification processes
The basis for understanding the carbon footprint of dehumidification is the latent heat of vaporization—the energy required to convert water from liquid to vapor. It depends on temperature and is calculated by the formula: latent heat of vaporization = 2501 - 2.38 × temperature (kJ/kg). Removing moisture from air requires performing the reverse process, which demands energy input.
On the psychrometric enthalpy–humidity ratio chart it is clear that different dehumidification methods (condensation, adsorption, ventilation) follow different thermodynamic paths and therefore have different energy consumption. The energy used for dehumidification translates into CO₂ emissions via the primary energy conversion factor, which typically ranges from 2.0 to 3.0 for electricity and from 1.1 to 1.3 for gas.
It is critically important to distinguish between the direct energy consumption of the equipment and its indirect impact on the main HVAC system. Ignoring the effect of dehumidifiers on chillers and boilers leads to a 40–80% error in emission estimates, especially for condensation systems that release heat into the space.
Energy and carbon profile of condensation dehumidification
Condensation dehumidification is based on the thermodynamic cycle of a refrigeration machine. Air is cooled below its dew point, moisture condenses, and then the air is reheated. The coefficient of performance (COP) of such a system depends on air temperature and usually ranges from 1.5 to 4.0 for temperatures from +5°C to +35°C.
The specific energy consumption of condensation dehumidifiers is defined as the ratio of electrical power to moisture removal capacity and typically is 0.4-0.8 kWh/kg of moisture. The heat released by the condenser into the space equals the sum of the latent heat of vaporization and the electrical input power, creating additional load on the building’s cooling system.
In addition to indirect emissions from energy use, condensation systems have direct emissions due to refrigerant losses. These are calculated as the product of the mass of refrigerant lost and its global warming potential (GWP). Current trends aim to replace high-GWP refrigerants with lower-GWP alternatives.
Energy and carbon profile of adsorption dehumidification
Adsorption dehumidification occurs through moisture uptake by a solid adsorbent (silica gel, zeolite, etc.). The process includes two phases: adsorption (lowering the partial pressure of water vapor, heating the adsorbent due to heat of wetting) and regeneration (heating air to 120–180°C, desorbing moisture, cooling).
The specific energy consumption for regeneration depends on the heating of air, the heat of desorption, and the effectiveness of heat recovery. Energy sources for regeneration may vary—electric heaters, gas burners, hot water, steam—each with a different carbon intensity.
Adsorption systems impose additional fan loads due to pressure losses, which also affects the overall carbon footprint. Regeneration temperature strongly influences the balance between energy consumption and capacity—higher temperatures improve desorption effectiveness but increase energy use.
Energy and carbon profile of ventilation dehumidification
Ventilation dehumidification is the psychrometric process of replacing humid indoor air with drier outdoor air. The effectiveness of this method depends on the difference in humidity ratio between outdoor and indoor air. Climatic feasibility is determined by analyzing hourly weather data and calculating the share of hours per year when the outdoor humidity ratio is lower than indoors.
Energy consumption for the thermal treatment of supply air includes heating during the heating season and cooling in summer. Heat recovery reduces this load by the fraction corresponding to recovery effectiveness (typically 0.5–0.85).
When compared with mechanical dehumidification, it is important to determine the economic effectiveness threshold, which depends on the difference in humidity ratio, temperature, and system efficiency. Ventilation dehumidification is often more effective in cold and dry climates.
Algorithm for selecting technology based on minimum CO₂ emissions
To select the optimal dehumidification technology by the criterion of minimum emissions, follow this algorithm:
- Determine the annual moisture removal requirement from the object’s moisture balance
- Calculate the specific energy consumption for each technology
- Account for the impact on the building’s main HVAC system
- Multiply energy consumption by the primary energy conversion factor and carbon intensity
- Add direct refrigerant emissions (for condensation systems)
- Sum emissions across the system boundary
- Compare technologies and select the optimal one
Boundary conditions for technology selection:
- If air temperature is below 15°C, adsorption dehumidification has an advantage
- If the outdoor humidity ratio is lower than the indoor for more than 4000 hours per year, ventilation dehumidification has an advantage
- If there is a consumer of low-grade heat, condensation dehumidification with heat recovery has an advantage
Heat recovery from condensation: calculating the potential for emission reduction
The heat available for recovery in condensation systems equals the product of moisture removal rate and latent heat of vaporization plus electrical input power. This heat can be used by various low-grade heat consumers: domestic hot water systems (heating to 50–60°C), swimming pools (heating to 26–28°C), air heating systems (heating to 35–50°C), and various industrial processes.
The temperature potential of recovery is determined by the condensing temperature, which for dehumidification at +20°C is typically 40–55°C. Heat exchanger effectiveness accounts for a minimum temperature approach (3–5 K), which affects the final usable heat.
Emission reductions occur by displacing boiler or heat pump operation. The economic feasibility of heat recovery depends on many factors, but typical payback periods range from 2 to 7 years, depending on utilization intensity and energy prices.
Methodology for calculating the total carbon footprint of a dehumidification system: the TEWI method
The TEWI (Total Equivalent Warming Impact) methodology allows assessing the total equivalent warming impact of a dehumidification system. For condensation systems, TEWI is calculated as the sum of three components:
1) The product of the global warming potential and annual refrigerant losses over the service life
2) The product of the global warming potential and the refrigerant charge multiplied by the difference between one and the recovery fraction at end-of-life
3) The product of service life and annual energy consumption and the carbon intensity of electricity and the primary energy conversion factor
For an adequate assessment, it is necessary to expand the system boundary to include the impact on chillers and boilers. For adsorption systems, the calculation is modified according to the energy source used for regeneration.
For a fair comparison of technologies, results are normalized to kilograms of CO₂ equivalent per kilogram of removed moisture per year or per square meter per year.
Integration with renewable energy sources: calculating carbon footprint reduction
Heat pumps for desiccant regeneration can provide a coefficient of performance of 2.0–3.5 for regeneration temperatures of 120–140°C, which significantly reduces emissions compared to direct electric heating.
Solar collectors for regeneration are sized by the formula: the required collector area equals the regeneration thermal energy divided by the product of average insolation, collector efficiency, and utilization factor. Collector efficiency is typically 0.4–0.7.
Photovoltaic systems for condensation dehumidifiers are assessed via the load coverage factor, which equals the product of PV system power and generation time divided by annual energy consumption.
A comprehensive assessment of integration with renewables must account not only for operational emissions but also for emissions from equipment manufacturing (embodied carbon).
Impact of grid carbon intensity on technology choice
The carbon intensity of electricity varies significantly by country: from 50 g CO₂/kWh (Norway, Sweden) to 800 g CO₂/kWh (Poland). This variation critically affects the optimal choice of dehumidification technology.
In countries with low carbon intensity (100 g CO₂/kWh), condensation dehumidifiers with a COP of 2.5 will have a lower carbon footprint compared to adsorption systems with gas regeneration. At high carbon intensity (700 g CO₂/kWh), the situation reverses.
The projected 50% decrease in carbon intensity by 2040 should also be considered in long-term planning. Purchasing green renewable energy certificates can significantly reduce the calculated carbon footprint.
Regulatory requirements and building environmental certification systems
The Energy Performance of Buildings Directive (EPBD) sets requirements for nearly zero-energy buildings (nZEB). The F-gas Regulation 517/2014 limits the use of refrigerants with high global warming potential: above 2500 (from 2020) and above 150 (from 2025).
Building environmental certification systems (BREEAM, LEED, DGNB) account for energy efficiency and CO₂ emissions from all engineering systems, including dehumidification. The TEWI method is often used in certification to assess refrigeration systems.
Trends in the regulatory field include tightening requirements: a full ban on high-GWP refrigerants, mandates for the use of renewable energy sources, and the introduction of carbon pricing.
Common engineering mistakes and misconceptions
When assessing the carbon footprint of dehumidification systems, the most frequent mistakes are:
- Comparing technologies solely by direct energy consumption without accounting for the impact on the HVAC system
- Applying a universal value of carbon intensity without considering the local generation mix (error up to 400%)
- Ignoring direct emissions from refrigerants
- Overestimating heat recovery potential without calculating a real sink and temperature matching
- Evaluating renewables by installed capacity without calculating the capacity factor
- Comparing adsorption dehumidification with electric regeneration instead of gas-fired regeneration
- Failing to account for performance degradation over the service life
- Ignoring embodied carbon from equipment manufacturing
Limits of applicability and conditions where approaches are ineffective
Even the most efficient technologies have their limitations:
- Condensation dehumidification: at temperatures below +5°C the COP drops below 1.5, making the method energy-inefficient
- Ventilation dehumidification: effective only when the outdoor humidity ratio is lower than indoors; not feasible in humid climates
- Heat recovery: at capacities below 50 kg/day the capital costs of recovery equipment are usually unjustified
- Solar regeneration: in Northern Europe (latitude above 55°) insolation below 1 kWh/m²/day provides less than 20% load coverage
- Regulatory limits on refrigerants with GWP above 150 reduce equipment choices
- Continuous dehumidification makes energy storage in batteries economically ineffective
Frequently asked questions
How should the carbon footprint of different dehumidification technologies be compared correctly?
For a correct comparison, it is necessary to: 1) define identical system boundaries for all technologies, 2) include both direct and indirect emissions, 3) account for the impact on the building’s HVAC system, 4) use local electricity carbon intensity, 5) normalize results to a common functional unit (kg CO₂-eq/kg of moisture).
Why is the difference in electricity carbon intensity so important?
When carbon intensity changes from 100 to 700 g CO₂/kWh, emissions from a condensation dehumidifier with the same COP increase sevenfold, which can fundamentally change the optimal technology choice. For example, at low electricity intensity, condensation systems usually yield lower emissions than gas-fired adsorption systems, and at high intensity—the opposite.
How to assess the economic feasibility of heat recovery?
You need to calculate: 1) available recoverable heat, 2) the real share of this heat that can be utilized considering temperature potential and temporal matching, 3) primary energy savings, 4) capital costs for the recovery system. A typical payback period should be less than 5 years for industrial facilities.
How to account for embodied carbon when selecting equipment?
Embodied carbon (emissions from equipment manufacturing) should be distributed over the entire service life and added to operational emissions. For dehumidification systems, embodied carbon usually accounts for 5–15% of total life-cycle emissions, but for systems with renewables (especially photovoltaics) it can reach 30–40%.
How do refrigerant regulations affect technology choice?
Restrictions on refrigerants with GWP>2500 (from 2020) and GWP>150 (from 2025) force a transition to alternative refrigerants, which may reduce the energy efficiency of condensation systems by 5–10%. These changes can make adsorption or ventilation systems more attractive in some scenarios.
Conclusions
Effective assessment and reduction of the carbon footprint of dehumidification systems require a comprehensive approach that accounts for both direct and indirect CO₂ emissions. The key principles to implement in design are:
- Expanding the system boundary in calculations—mandatory consideration of the impact on the building’s main HVAC system
- Using the TEWI methodology with adjustments for local energy carrier carbon intensity
- Prioritizing heat recovery and integration with renewable energy sources
- A differentiated approach to technology selection depending on climatic conditions and operating modes
- Accounting for future regulatory changes and the projected decarbonization of energy systems
Design engineers should abandon one-size-fits-all solutions in favor of an object-oriented approach. In some conditions, the optimal choice will be condensation dehumidification with heat recovery; in others—adsorption with gas regeneration or ventilation with heat recovery.
Only by integrating carbon footprint assessment into building life-cycle analysis methodologies can we achieve real CO₂ emission reductions and move toward climate-neutral construction and operation.
