Technological advances and concerns about global warming that is leading to Increase in temperatures, have completely revolutionised HVAC systems that re-engineer indoor climate, observes Sapna Kulshrestha.
No good design project is complete without an emphasis on the HVAC system – climate control systems that regulate indoor temperature and humidity levels, and are available in a broad spectrum of sizes and complexities.
The kind of system you use would depend on the size of your space. As Sunjay Porwal, principal architect, Kalayojan, says, “Window ACs and split ACs are good for small spaces; but where large volumes are involved, central air-conditioning systems of ductable packaged air-conditioner or central plants are preferred.”
The Indoor Air Management System
One of the hottest topics of debate in the HVAC industry is how you can maintain indoor air quality (IAQ). The focus for HVAC engineers today is not only on the environment, but also what has now come to be known as the ‘invironment’.
The reason isn’t hard to find: most commercial buildings these days are predominantly glass structures with a centralised air-conditioning system, and its occupants have no control over their environment. The indoor air circulation is often far from perfect, and could even be harmful to the health of people working there.
Amitesh Poddar, sales manager for Daikin India in the Maharashtra region, says, “Because of faulty HVAC systems, people suffer from health problems such as the Sick Building Syndrome, which particularly results because of the contamination of the indoor environment due to the growth of bacteria, fungi, mold, viruses and mildew (that are collectively termed micro-organisms) which spread through the re-circulation of the stale indoor air.
“In fact, new methods are constantly being defined to maintain the quality of indoor air – such as humidity and temperature sensors that help to maximise air quality, and CO2 sensors that improve the indoor air environment.”
An important part of maintaining indoor air quality is natural air-ventilation, which enables dilution and gradual removal of pollutants.
However, infiltration of even a small quantity of outside air into the air-conditioned space can raise HVAC plant requirements dramatically.
Also, the removal of pollutants solely by the use of an effective ventilation system is slowed down by the fact that some dust particles and other matter are trapped inside carpets, drapes and other such surfaces, only to be released into the air later.
Nitin Tiwari, sales head of Bluestar India (Mumbai & Goa region), feels, “A combination of pollutant control, filtration, air-cleaning and ventilation can be the ideal mix for improving indoor air quality.
In conventional HVAC systems, air filters, ionisers and electrostatic precipitators have been effectively removing microscopic particles such as dust and smoke, but they do not totally purify and revitalise the air.
There is another, more commonly employed system in commercial buildings and hotels – the UV light treatment. Installed in the main supply or return duct of an air-source heat pump or air-conditioning system, UV lights disinfect the air stream as it passes through the HVAC system repeatedly.
However, this system is a high-end product and is used only by premium segment institutions.”
TRANE’s CleanEffects air filters that utilise advanced air-cleaning technology to remove up to an astounding 99.98 per cent of airborne allergens from the stale indoor air, is one of the most recent innovations in HVAC systems.
It contains alternately-charged layers of filter for stronger and more effective pollutant collection of up to .1 micron in size. Moreover, its unique surface does not get clogged so as to hamper air flow.
Treated Fresh Air (TFA) Units offer complete solutions for Indoor Environment Quality. It is also energy-saving.
Due to low energy constraints and the ever-increasing demand for fresh air, conventional TFAs are increasingly being replaced with TFA units that incorporate ‘energy recovery devices’ (also known as Energy Recovery Ventilators or ERVs).
The ERV preconditions fresh outside air before it is introduced into a building, thus allowing for reduction in air-conditioning tonnage. Among the various types of heat recovery devices used, the best option is the Modern Rotary Heat Recovery Wheels (HRW), which offers air-quality enhancement, humidity control and energy conservation, all of them simultaneously.
Sumant Padhi, sales head, Western region, Desiccant Rotors International, talking about their recent TFA product, says, “Our EcoFresh range of fresh air treatment equipment includes ERVs and TFAs that allow HVAC designers to design systems with more ventilation, even while they keep energy costs low.
Ecofresh Rotary Heat Recovery Wheels (HRW) exchange the energy from the exhaust air to incoming fresh air, while desiccant (absorption material) removes pollutants and inbuilt purge sector eliminates cross contamination due to mixing of supply air and exhaust air streams through leakage or carryover. This ensures the indoor air quality as well as saves energy.”
While there have been major technological advancements in terms of indoor air quality equipments, the conventional HVAC systems too have undergone innovative improvements, making them more energy-efficient and technically-advanced compared to earlier systems.
In the packaged air-conditioners segment, the commonly-used water-cooled models (where water is used as refrigerant) or air-cooled models for areas where water is scarce or of hard quality or where there’s no space for installing cooling tower, now come with electronic controls and even microprocessor control with the system, which gives them the added advantage of better precision, energy efficiency and reliability.
Sreenivas Iyer, branch manager (Mumbai), Carrier Air-conditioning & Refrigeration Ltd, says, “The Carrier package unit houses the innovative technology of the Scroll Compressor that guarantees high volumetric efficiency and low friction losses, along with microprocessor controller display – which is especially suited to Indian conditions such as wide operating voltage and economical running.”
The most commonly used central plant systems such as the Vapour Compression Chiller System and the Direct Expansion (DX) system have also seen technological changes, and so have environment-friendly refrigerants.
For instance, LG’s new specialised and optimised direct expansion air-conditioning systems called Multi F DX is equipped with inverter technology and R410a refrigerant that adds energy efficiency, low noise and low maintenance features. Similarly, in chilled water systems, the air-cooled condensers now offer greater advantages over water-cooled condensers of up to 200 TR, as they are more economical on the lifecycle basis.
The electrical-driven chilled water system has also seen increased efficiency after the application of energy management technology called the Variable Frequency Drive (VFD).
Based on the fluctuation in the air-conditioning demand from the end-user or due to climatic fluctuations, VFD changes the frequency and the rpm of the motor, thereby resulting in the saving of energy.
Also considered the next generation intelligent and energy-efficient air-conditioners, they come with a highly sophisticated electronic control centre that enables zone-wise climate control.
A recent development in HVAC equipment is the Variable Air Volumes (VAV), which provides air-distribution optimisation by tuning the volume of air according to the load at the end-user area.
All major players in the HVAC industry offer this technology as it is cost-effective and viable for even smaller applications. Variable Frequency Drives can be retrofitted to the existing equipment – saving up to 40% energy, while some of the newer HVAC equipment comes with built-in VFDs.
Blue Star, which has partnered with Danfoss, Denmark, as its Energy Solution Partners, now offers VFDs along with Power Saving Services in air-conditioning for commercial complexes.
Apart from vapour compression chillers, vapour absorption chillers driven by hot water are often used in spaces where the heat source, such as natural gas, is available and cheap. These are getting popular because of their low requirement of a small amount of power even for higher capacities of refrigeration.
They can also be powered by low-grade waste heat from the plant or extra steam from the boiler.
While chiller systems or compression refrigeration systems require a large amount of power, the absorption refrigeration system’s small pump requires a small amount of electric power for pumping refrigerant-absorbent solution.
As Tiwari explains, “In absorption chillers, the compression of the refrigerant (water) is done by its absorption through the absorbent (lithium bromide) for cooling, which does not produce the greenhouse effect. Due to absence of a compressor and several moving parts, it has added advantages: low maintenance and low noise. It is mostly used by industries that have availability of natural gas and do not require comfort air-conditioning.”
Humidity control for hot and humid areas is a big challenge for the HVAC industry, especially when it comes to maintaining the ambient levels in indoor air. As architect Rupam Dey says, “Maintaining humidity levels can eliminate the potential for mold, mildew formation and bacteria growth, thus playing a huge part in the longevity of a property’s room furnishings and ambience.”
Dehumidification has now become a key feature for every HVAC system, and it has also brought a paradigm shift in the HVAC design approach. For instance, HVAC systems are adopting Dedicated Outdoor Air Supply (DOAS) units to deliver pre-conditioned air to individual spaces and remove space-sensible cooling load through traditional HVAC equipment.
The mechanical dehumidification system is now being replaced by advanced system of rotary desiccant dehumidifiers, which use silica gel, activated alumina, molecular sieves and metal silicates in honeycomb-type matrices (or more commonly, rotary type) to provide a high surface area for exchange of moisture and/or temperature (sensible heat).
Ajay Kumar, director, Felicity Machines Pvt Ltd, manufacturers of dehumidifiers with in-built A/C, says, “The Rotary desiccant air-conditioning system combines the technologies of desiccant dehumidification and evaporative cooling; it is free from CFCs, uses low energy and provides humidity as well as temperature management.”
Additionally, CO2 monitors and controllers are being used to supervise and control CO2 concentration in occupied spaces, room temperature and humidity. They display the CO2 levels in air and control the opening and closing of a set of relay contacts to bring in fresh air in order to reduce the CO2 levels. Rajiv Puri, senior director, design management, APAC, Marriott International, agrees.
“For hotel areas like pubs and restaurants, CO2 sensors can ensure that fresh air is introduced in sufficient volume without over-ventilating – so that energy could be saved and the quality of indoor air could be optimised.”
Re-engineering Air Distribution
Besides technological improvements in HVAC systems, there have also been radical changes in the designing and execution of air-distribution systems that mainly consist of supply and return air ducts, dampers, diffusers and grills.
Porwal adds, “A good practice to follow is to keep the HVAC plant in the direction of the natural airflow and to plan ducting in such a way that it avoids mixing of return air with other air, dust and moisture through openings in partitions above false ceilings.
Also, narrower ducts may create a humming noise problem, which can be avoided by following optimal design specifications.” Moreover, with the availability of computer-designed and machine-made ducts, diffusers and grills, effectiveness of air flow and overall HVAC efficiency has risen considerably.
Increasingly, the Building Automation System (BAS) has all equipment, including pumps, AHUs and cooling towers, connected to the centralised system. Honeywell, Siemens and Schneider Electricals are some of the major companies offering such state-of-the-art automation products.
The BAS helps operate the AHUs (Air Handling Units) and also automatically maintains proper temperature, humidity, air-flow, cooling tower, water temperature and pressure.
Vinayak Sane, director, Elmark Engineers, cites an example. “In an intelligent cold water chiller, the power required to attain the desired set point would be less compared to, say, a non-automated one leading to environmentally-efficient HVAC solutions.”
The use of PLCs (Programmable Logic Controllers) is the latest in HVAC automation systems, where the zone-based temperature sensors provide feedback to the controller to deliver heating or cooling as needed. The implementation of wireless technology for networking HVAC controllers, which often use sensors, will eventually cut installation and labour costs.
Carrier has also developed an advanced technology called Carrier Comfort Network (CCN) that provides centralised control and management of several chillers and automatic switch on/off for operation that balances optimisation and building control management while simultaneously integrating reliable Direct Digital Control (DDC) technology with the HVAC equipment.
With growing awareness about green buildings, technological innovations in the HVAC industry and energy-efficiency are being driven by concerns for sustainability.
In a major shift during recent years, conventional refrigerants such as CFC, R12 and R22 have been replaced with eco-friendly products. Globally, the HVAC industry has now switched to safer chlorine-free refrigerants like R134a, R407c, R404a or other similar HFCs (HydroFluoroCarbon).
Poddar adds, “R134a, an HFC, is a permanent refrigerant, has no phase-out requirement and is most preferred for all types of central air-conditioning plants for a green building.”
Also being promoted are air-pollution control devices like air scrubbers, wet scrubbers and gas scrubbers in HVAC plants that use high-energy liquid spray to remove aerosol and gaseous pollutants from an air stream.
The various scrubbers are commonly used to help control emissions of sulphur in the atmosphere. As Ketaki Narain, director, Corporate Communications of The Oberoi Group explains, “In our hotels, wet scrubbers have been installed in the generator and boiler exhaust systems to reduce the emission levels of sulphur dioxide, nitrogen oxide and particulate matter in the surrounding air.”
Interestingly, geothermal energy is the new source of energy being utilised in the alternate energy-efficient systems in vogue today.
A geothermal heat pump system consists of a heat pump, an air-delivery system (ductwork), and a heat exchanger. In winters, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In summers, the process is reversed and the heat pump moves heat from the indoor air into the heat exchanger.
Solar India Solutions is one of the few companies in India to offer this technology. CEO Chandra Shekhar says, “We have introduced the new global power-saving technology known as the Geo-Exchange System or the Ground Source or Water Source heat pump system that is adaptable to the ground source (geothermal-renewable energy) or water source (conventional energy) cooling towers.”
As the significance of green living and technological innovations are felt further throughout the globe, experts feel that the use of new tools such as the Building Automation System and energy-efficient HVAC systems will gain centre-stage in the HVAC industry.