Understanding the chemistry and behaviour of pool air contaminants is essential to designing ventilation systems that protect swimmer health and building fabric.

Chemical compounds formed when chlorine reacts with nitrogen-containing organic matter introduced by swimmers — primarily urea, sweat, and other body waste. Chloramines exist in three forms: monochloramine, dichloramine and trichloramine. They are the primary cause of the characteristic ‘pool smell’ and are a leading source of indoor air quality problems in pool halls.

The most volatile of the three chloramine compounds and the main chloramine found in the air above chlorinated pools. Trichloramine off-gases readily from pool water into the surrounding air, where it settles in the breathing zone due to its density. It is a known respiratory irritant and is highly corrosive to metals, electronics and building fabric.

The two waterborne forms of chloramine, monochloramine and dichloramine, remain in solution until destroyed by UV or ozone treatment or until further reaction with chlorine converts them to trichloramine, at which point they off-gas and become air quality concerns.

The range of chemical compounds formed when disinfectants such as chlorine react with organic and inorganic matter in pool water. Chloramines are the most prevalent class of DBPs in indoor pools. Other significant DBPs include trihalomethanes (THMs) such as chloroform. Effective ventilation is one of the primary means of managing DBP concentrations in pool air.

The area of a pool hall at swimmer head height, typically 1–2 metres above the pool deck. Because trichloramine is denser than air, it tends to accumulate at low levels rather than dispersing upward, concentrating in the breathing zone closest to the water surface. Effective ventilation design must deliver conditioned fresh air directly into this zone rather than simply circulating air at higher levels.

A passive plate heat exchanger that transfers thermal energy from warm exhaust air to incoming fresh air without the two airstreams mixing. In a pool air handling unit, the recuperator sits at the core of the heat recovery system, pre-heating supply air before it enters the pool hall. This reduces the energy required to condition incoming fresh air, directly cutting operational carbon and running costs.

The process of capturing thermal energy from exhaust air and transferring it to supply air. In indoor pool ventilation, heat recovery is particularly valuable because pool halls are continuously ventilated at high air change rates to manage humidity and chloramine levels, meaning large volumes of warm air are constantly being exhausted. Recotherm air handling units utilise effective heat recovery which reclaims a significant proportion of this energy before it is lost.

A measure of how effectively a recuperator transfers thermal energy from exhaust to supply air, typically expressed as a percentage. Higher efficiency means less supplementary heating is required to bring supply air up to the desired temperature, reducing energy consumption.

Efficiency is influenced by the thermal conductivity of the heat exchanger material, the surface area available for heat transfer and air flow rates. Recotherm use coated aluminium recuperators, rather than polymer composite, because of the superior thermal conductivity, ease of maintenance and structural strength.

A material property describing how readily heat passes through a substance.

Aluminium has a thermal conductivity of approximately 205 W/mK, making it highly effective as a heat transfer medium in recuperators, unlike polymer composites, which typically exhibit thermal conductivity values of 0.1–0.5 W/mK. You can read more about this here.

An assessment of the total cost of owning and operating a system over its full service life, including capital cost, energy running costs and maintenance. Whole-life cost analysis is the appropriate framework for evaluating pool ventilation systems, as it captures the long-term energy savings delivered by efficient heat recovery and the reduced maintenance associated with durable components.

A working fluid used in a refrigeration or heat pump cycle to transfer heat from one location to another. In pool dehumidification systems, refrigerants absorb heat from moist exhaust air (causing moisture to condense) and transfer that heat to pool water or supply air.

The environmental credentials of the refrigerant used, particularly its global warming potential (GWP), are a key consideration in sustainable system specification.

A measure of how much heat a given greenhouse gas traps in the atmosphere over a defined time period, relative to carbon dioxide (CO₂ = 1).

Refrigerants vary significantly in GWP: common HFCs such as R410A have a GWP of approximately 2,088, while natural refrigerants such as CO₂ (R744) have a GWP of 1. Lower-GWP refrigerants are increasingly mandated or incentivised under F-gas regulations.

Transitional HFCs such as R32 (GWP 675) represent a lower-GWP alternative to R410A, though they remain subject to F-gas regulation.

A class of synthetic refrigerants widely used in HVAC and refrigeration systems due to their effective thermodynamic properties. HFCs do not deplete the ozone layer, but many have high global warming potentials, making them a significant contributor to climate change when emitted.

Common HFCs in HVAC include R134a, R407C, and R410A. HFCs are subject to phase-down under UK and EU F-gas regulations.

A newer class of refrigerants developed as lower-GWP alternatives to HFCs. HFOs have a double carbon bond that causes them to break down more rapidly in the atmosphere, resulting in GWP values typically below 10.

Examples include R-1234yf and R-1234ze. HFOs are not subject to the HFC phase-down under current F-gas regulations and represent a compliant alternative for many applications, though some HFO blends containing HFC components may still fall within F-gas scope.

Legislation controlling the use, containment and phase-down of F-gases, including HFCs. The EU’s revised F-gas Regulation (EU 2024/573), which came into force in March 2024, significantly accelerates the phase-down of HFCs, with a target of full phase-out of virgin HFCs by 2050.

Great Britain maintains its own F-gas regulatory framework under the retained Fluorinated Greenhouse Gas Regulation, enforced by the Environment Agency. Defra ran a consultation in late 2025 on tightening the GB HFC phase-down schedule, but confirmed in May 2026 that it will not legislate in 2026 to change the phase-down steps from 1 January 2027. The regulations drive the HVAC and refrigeration industry towards lower-GWP refrigerant alternatives.

An approach to pool dehumidification and heat recovery that does not rely on a vapour compression refrigerant cycle. By eliminating refrigerant from the system, refrigerant-free designs avoid F-gas compliance requirements entirely, remove the risk of refrigerant leakage and are insulated from future regulatory changes affecting HFC availability and pricing. Recotherm’s Aeris and Artis units are designed on this principle, offering a refrigerant-free alternative.

Refrigerants that occur naturally in the environment, including carbon dioxide (CO₂/R744, GWP 1), ammonia (R717, GWP 0) and propane (R290, GWP 3).

Natural refrigerants are increasingly favoured as low-GWP alternatives to HFCs, particularly as phase-down schedules tighten. However, they present their own handling and safety considerations: ammonia is toxic and propane is flammable so both require careful assessment in occupied public buildings such as leisure centres. CO₂ is generally considered the most viable natural refrigerant option for pool hall applications.

A regulatory requirement under F-gas regulations for equipment containing above-threshold quantities of fluorinated refrigerants. Operators of systems containing F-gases must arrange periodic leak checks by certified engineers, with frequency determined by the refrigerant charge size and GWP. Leak testing represents an ongoing compliance and maintenance cost for refrigerant-based systems.

A software and hardware platform that monitors and controls a building’s energy-consuming systems including HVAC, ventilation, heating and lighting with the aim of optimising performance and reducing waste.

A BEMS collects real-time data from sensors and meters throughout the building, identifies inefficiencies and either automatically adjusts system operation or guides operators with recommended actions. Well-implemented BEMS can reduce energy consumption by 15–30% compared to unmanaged operation.

All Recotherm units are equipped with a BEMS microprocessor which means we can ensure that the unit is always operating at maximum efficiency, minimising energy consumption.

A control and monitoring system for a building’s mechanical and electrical services. While a BMS focuses primarily on controlling systems, maintaining setpoints, managing schedules and providing operator oversight, a BEMS extends this with energy analytics, performance diagnostics and efficiency optimisation.

The two terms are sometimes used interchangeably, though BEMS implies a stronger emphasis on energy management intelligence.

A ventilation strategy in which air supply rates are varied in response to actual occupancy or air quality measurements, rather than operating continuously at design maximum rates.

In pool environments, DCV can significantly reduce fan energy consumption during low-occupancy periods. Sensors measuring humidity, chloramine proxies or CO₂ concentration can trigger increased ventilation when bather loads rise and reduced airflow when the hall is quiet.

Recotherm units contain fully modulating heating valves, fans and dampers which improve the energy-efficiency of the fans by up to a third compared to other units on the market.

An electronic device that controls the rotational speed of a motor, and therefore the output of a fan or pump, by varying the frequency of the electrical supply.

VSDs allow ventilation fans to modulate their output in response to demand rather than running at a fixed speed. Because fan power varies with the cube of speed, even modest reductions in fan speed deliver substantial energy savings. VSDs are fundamental to energy-efficient, demand-responsive pool ventilation and form a key part of Recotherm’s in-house control strategies.

A type of brushless DC motor controlled by an integrated electronic circuit, offering significantly higher efficiency than conventional AC induction motors, particularly at part-load conditions.

EC motors are commonly used in energy-efficient fans such as ZA bluefin fans, used in Recotherm units, where they enable precise speed control and low energy consumption across a wide operating range.

A target value for a controlled variable ,such as temperature, relative humidity or air change rate at which a control system aims to maintain operation.

In pool ventilation, key setpoints include pool hall air temperature, relative humidity and fresh air supply rate. Optimising setpoints to match actual facility needs (rather than over-ventilating or over-conditioning) is a significant source of energy saving.

The connection of environmental sensors measuring temperature, humidity, CO₂, occupancy or air quality to a control system or BEMS to enable data-driven operation. Sensor integration allows a ventilation system to respond dynamically to actual conditions rather than running to fixed schedules, improving both air quality management and energy efficiency.

The ability to access, review and act upon building system performance data from an off-site location via a network connection.

Remote monitoring allows Recotherm’s skilled service engineers to track energy consumption, identify faults and adjust system operation without being on site which reduces response times and enables proactive maintenance.

The carbon dioxide equivalent (CO₂e) emissions generated by the energy consumed in operating a building or system over its lifetime. In pool facilities, operational carbon is dominated by the energy required for heating, ventilation, dehumidification and water treatment.

Reducing operational carbon through efficient system design and heat recovery is the primary lever for delivering net zero pool facilities.

The carbon emissions associated with the manufacture, transport, installation, maintenance and end-of-life disposal of building materials and components.

Embodied carbon is distinct from operational carbon and is estimated to account for approximately 20–50% of a new building’s whole-life carbon footprint. For pool ventilation systems, embodied carbon considerations include material selection, component longevity and end-of-life recyclability. This is why all materials used in Recotherm AHUs are fully recyclable.

The total carbon footprint of a building or component across its entire lifecycle, combining both operational and embodied carbon.

Whole-life carbon assessment is the most complete basis for evaluating the sustainability of building systems, as it prevents the false economy of specifying low-capital-cost equipment that carries a high carbon penalty through short service life or high energy consumption.

A state in which the total greenhouse gas emissions associated with a building or organisation are balanced by equivalent carbon removals or offsetting, with offsetting generally reserved for residual emissions that cannot be eliminated.

In the built environment, achieving net zero requires addressing both operational carbon (through energy efficiency and decarbonised energy supply) and embodied carbon (through material selection and circular economy approaches).

A standardised unit for measuring greenhouse gas emissions that expresses the warming effect of different gases relative to carbon dioxide.

For example, a refrigerant with a GWP of 2,088 released into the atmosphere is equivalent to releasing 2,088 times its mass in CO₂. CO₂e enables direct comparison of the climate impact of different gases, systems and activities.

The UK government’s policy framework, published in 2021, for decarbonising heat in buildings as part of the path to net zero by 2050.

The strategy sets out a trajectory away from fossil fuel heating towards heat pumps, district heat networks and energy-efficiency improvement. Subsequent policy development under the current Labour government, including the Warm Homes Plan, has built on this direction of travel.

For pool operators and facilities managers the cumulative policy signal is clear: low-carbon heating technologies are the expected direction for new and retrofitted building systems.

An economic model designed to eliminate waste and maximise the value of resources by keeping materials in use for as long as possible.

In the context of pool ventilation systems, circular economy principles apply to component longevity (extending service life to defer embodied carbon from replacement), repairability and end-of-life recyclability.

Recotherm units meet this need as they have a typical service life of 25+ years, are designed for ease of maintenance and all parts are fully recyclable at end of life.

A framework for categorising an organisation’s greenhouse gas emissions.

Scope 1 covers direct emissions from owned or controlled sources (e.g. gas boilers).
Scope 2 covers indirect emissions from purchased electricity, heat, or steam.
Scope 3 covers all other indirect emissions across the value chain, including those from purchased goods and services.

For pool facility operators, Scope 1 and 2 emissions from heating and electricity are the primary focus of net zero strategies.

Whether you’re at concept stage or already deep into design, the Recotherm team is here to help. The earlier we’re involved, the more we can do but it’s never too late to get the right advice on humidity control and ventilation for your pool project.