Feature dehumidification in order that fresh air is introduced at the same moisture level as the ideal building climate .
In summer , in hot dry environments like the highveld , the constant use of air-conditioning to keep the building space cool , has a negative drying effect , where adiabatic cooling with humidification with fresh air make-up would be energy friendly resolution of this issue .
COOLING FOR FREE ON OFF-PEAK SCENARIOS USING ADIABATIC METHODS . Andersen gives the example of a situation where a building is cooled using evaporative cooling methods , using a contact media associated method . “ Say it was using fresh air to do free cooling , circulating fresh air with a blend of building air , and the refrigeration compressors would only switch on when the humidity as well as temperature bands got breached — then refrigeration needed to be used .”
“ An innovation is ‘ indirect cooling ’, where you ' re able to do the same amount of cooling but without adding moisture to the air still using the evaporative method , by utilising a heat exchanger with the adiabatically cooled wet-bulb air or water . Another alternative is to use cooling towers , which aren ' t as efficient from a wet-bulb approach , so the direct contact evaporative media is still the most efficient option .”
“ Large hyper scale data centres use massive amounts of energy on racks so their power utilisation efficiency is required to be under one . They use contact evaporative media for direct and indirect cooling , either two stage or single . High moisture content in the air means that you can ' t have high humidity leaving the system going into the building space , so one needs to be able to cool that air without adding moisture . This is accomplished using the energy-friendly indirect method . Project owners might not like it because the opex cost can be a little higher than standard air conditioning because it requires additional maintenance — but that maintenance cost is much less than the energy cost saving ; a worthwhile ROI .”
Andersen notes that the concept of ‘ full lifecycle cost ’ is extremely important in designing an HVAC system , with a five-to-seven-year lifecycle being the optimum for contact media . This model looks at issues such as predictive analysis to look at water quality and its potential to create scaling as water evaporates to leave salt . The elements therefore can be changed while the base system can continue because it ' s made out of high-quality steel that ’ s good for 15 – 20 years .
ENERGY CONSIDERATE DECISIONS “ Dehumidification is generally expensive if not specified using the correct method for the associated condition . There are other highly efficient methods with a cooling coil using
Glsun Mall / Unsplash refrigerant , which is extremely efficient for dehumidification at high temperatures and high humidities . Beyond that point , the efficiency of the plant from a coefficient of performance perspective needs to be evaulated : The COP drops with temperature . The energy consumed by the plant gets higher compared to the kilowatts of output of the plant as the temperature drops ,” says Andersen .
“ It depends on what humidity you want to dry the air to — if it ' s within the realms of human comfort then HVAC does an extremely good job . However , if you ' re able to use waste heat from your cooling plant , then the sorption dehumidification method starts becoming exciting . You ’ re
already cooling the building and have a large amount of energy available from your air conditioning plant in the form of hot gas with mild 55 degree water available that can be used to regenerate a desiccant wheel which does the rest of the dehumidification for free to save a lot of energy on the latent load .” Coils are designed to have a high sensible ( real energy temperature removal portion versus a latent portion — moisture content removal ). Cooling coils are typically designed to remove heat and if they have to remove a lot of moisture then the efficiency of the coil is compromised against the design standard .”
“ Finally , it also depends on where you are — for example Durban having a high moisture content . Having a combination system to reduce the moisture content of the air to bring the air to dew point and then using desiccant humidification thereafter to do the rest of the work to achieve a lower humidity setpoint is actually more efficient . It ' s not as energy efficient below 18 degrees air-on to use the refrigeration method as compared to desiccant . There is a balance point where using refrigerants is not much more economical from a kilogram per watt consumption perspective than compared to using desiccant . Combination desiccant and refrigeration cooling has a higher capital cost associated with it , but long term the machines last 15 to 20 years to give a good return on investment ,” says Andersen . RACA
High tech industrial park .
www . refrigerationandaircon . co . za RACA Journal I March 2023 31