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Airconditioning for large spaces

In the recent years, there has been an increase in the regulatory requirements regarding indoor air quality and energy savings in large commercial area projects. This affects a considerable number of projects: not only new construction, but also the renovation part.

 

From the point of view of the property, it is very interesting. Due to the economic repercussion it has, to underline that the main objective of these projects is to install air conditioning systems with greater energy efficiency.
The current trend in air conditioning is towards new control technologies, energy recovery, inverter or electronically commutated motors or new lower GWP refrigerant gases, as well as the use of water-cooled loops or heat energy transport loops to reduce the refrigerant volume of the facilities.

Fundamental role of air quality

However, from a design point of view, it should not be forgotten that indoor air quality must also play a fundamental role in the design of the installation, so that the ventilation levels and the characteristics of the supply air are kept within the adequate working ranges to achieve optimum levels of temperature, humidity and concentration of carbon dioxide in the environment.

 

Finally, the use of new technologies such as the storage in the cloud of large volumes of data, obtained through supervision systems, makes it possible to analyze the operation of the installation so that maintenance engineers can debug the control parameters of the installation and equipment to achieve maximum energy savings under real operating conditions.

 

All these circumstances mean that, to the traditional design considerations of this type of facilities, all the current technological demands and trends are added, which has caused an increase in options in the market when selecting the most suitable equipment and options. Suitable for each project.

Building layout

The factors that must be taken into account in the design of new large-area buildings or in the renovation of existing ones are those related to the improvement of the insulation of the envelope, the use of radiation protection elements. solar, etc. However, large surfaces are buildings whose energy demand is more sensitive to other factors that are more difficult to control, such as occupation, which is highly variable, and the associated ventilation loads.

 

It is very important to keep in mind their zoning, taking into account the different uses of each of the zones. We can distinguish, in a generalized way, different areas that have their own characteristics when establishing the thermal needs for the selection of air conditioning systems, such as the mall and common shops, entertainment venues and educational objects.

 

It is also necessary to take into account the following aspects when evaluating the thermal demand of the building. Regarding internal loads, high occupancy and high level of lighting. On the other hand, the high flow rates of outside air, a function of occupancy, as well as the high associated loads that are highly variable over time. Not forgetting the more than possible simultaneous cooling and heating needs at certain times of the year.

Indoor environmental quality

Since most of the uses of large areas are related to commercial service activities, whether they are sales areas or leisure areas (restaurants, etc.), it is very important to design the building keeping in mind the achievement of a quality level of adequate indoor air, in order to preserve the well-being of the users and the hygiene, both of the building itself and of the merchandise displayed in the sales areas. In this regard, the thermal quality of the environment and the quality of the indoor air must be taken into account.

 

Regarding the thermal quality of the environment, it is necessary to consider an operating temperature in cooling ≥ 26°C and in heating less than ≤ 21°C as well as a relative humidity between 30-70%. Regarding the quality of the indoor air, the main factors are the contribution of the outside air for ventilation and its filtration.

 

The design parameters of Indoor Air Quality are defined in the RITE, through tables 1.4.2.1, 1.4.2.3 and 1.4.2.5, which provide the necessary filtration class, the ventilation rate and the value of the CO2 concentration. minimum admissible. The IDA3 class is required in this type of installation.

Energy efficiency

In relation to energy efficiency, the recent European Union Ecodesign regulations, also called ErP, mark the minimum values of seasonal energy performance of the equipment to free cooling by outside air (PFn> 70 kW), heat recovery from the extraction air (Qae> 0.5 m3 / s), the use of renewable energies, such as geothermal or aerothermal, or residual, as well as energy transfer between different areas of the building are possible measures to adopt to improve the energy efficiency of the entire installation.

Heat recovery in air conditioning units

The recovery of heat from the extraction air, in most cases, is a mandatory requirement to be taken into account in the design of air conditioning installations in this type of building. As the regulations have increased the requirements related to indoor air quality, recovery appears as an increasingly necessary measure to reduce the increase in energy cost involved in the thermal treatment of the fresh air flow. Likewise, energy saving regulations require that the efficiency values ​​of heat recovery units are also increasingly high.

 

Traditionally, cross-flow plate type heat recovery equipment or rotary exchangers have been incorporated into air treatment equipment, solutions that are usually quite bulky and with a higher consumption of fans. In this sense, these solutions can be envisaged in new construction, but in existing works under renovation, it is more their incorporation.

Dynamic thermodynamic and active recovery

In this way, new recovery systems based on refrigeration cycles have been developed that replace or complement the previous systems and that make it possible to meet the required regulatory requirements without substantially modifying the dimensions of the old units, finding different proposals on the market.

 

Thermodynamic recovery consists of mixing the exhaust air with the condensation / evaporation air in the outdoor unit, improving the working conditions of the refrigeration cycle and, consequently, increasing its energy efficiency.
Dynamic recovery consists of passing the extraction air through an additional coil where the refrigerant in liquid state is sub-cooled, increasing the capacity and efficiency of the machine.

 

Active recovery consists of adding an additional refrigerant circuit in the machine, which works on the extraction flow and the internal air flow in more favorable conditions and with high energy efficiency.
A solution that can be applied to large areas already built is to include a compact and independent ventilation unit with active recovery of the extraction air by refrigeration circuit.

Equipment VS requirements

Currently, the market offers a multitude of innovative equipment and technologies that allow meeting the new regulatory requirements. Thus, for food distribution areas, manufacturers such as Keyter, offer equipment with heat recovery batteries that make it possible to take advantage of the condensation heat of the refrigeration units used in these spaces, with an estimated saving in global electricity consumption between 15% and 20% in periods where the heating thermal load predominates.

 

To comply with the F-Gas, which entails a drastic reduction in the use of greenhouse gases in the coming years, heat pumps or chillers with refrigerants with a GWP close to 1 are being imposed, such as HFOs and even propane. For rooftop units, equipment with R513A is developed, in order to offer a low GWP solution that is type A1 to be used in this type of installation.

 

To meet the performance requirements of the different ErPs, new benchmarks have been developed to determine the seasonal efficiency of the units, the SEER and the SCOP, and minimum values ​​have been set for each type of equipment to be met in 2018 and in 2021. In order to increase the performance of the units, equipment has been developed with compressors mounted in tandem or in trio, increasing the capacity stages of the equipment, and units with inverter compressor, which allow adapting the consumption of the units to the demand on the premises.

Dehumidification process

Together with the above, it is found that the increase in the requirements for renewal air ventilation causes in many geographical areas the increase in latent loads, so that in the control of the interior environment, not only the regulation of temperature should be considered, but also about humidity. In order to offer solutions that improve the ability to control humidity, options have been developed for autonomous equipment, such as the incorporation of a post-heating battery that recovers part of the condensation energy of the unit to control the air temperature. of impulsion in the dehumidification process.

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