Dual Path Technology based AHUs can save up to 50% energy in air conditioning.
Three most important selling propositions flaunted by all HVAC equipment manufacturers are energy efficiency, energy efficiency and energy efficiency.
Chiller manufacturers world over have been responding by trying to squeeze even more out of their systems. For example, the efficiency of chillers has risen slowly to the point to which the latest generation offers peak-load efficiencies 25 percent higher than those of 10 years ago.
Changes in control systems and the use of variable-frequency drives have improved part-load efficiencies of chilled water production and transmission.
We can safely say that the production and transmission of cooling has been the major thrust areas but the Demand Side Management (read Air Handling Unit) has remained as inefficient as it was a century back.
However, consistently rising operating expenses due to perpetually escalating energy costs are forcing facility owners/managers to look for new ways to improve the operating efficiency of their energy guzzling air conditioners.
Conventional Air Handling Units
Air Handling Unit (AHU) in its present day avatar is not at all energy efficient, especially in Asian continent due to following reasons.
Major part of the hinterland in the continent often has fairly dry summers having specific humidity in the range of 5 to 10 gms/Kg at dry bulb temperatures often touching 50 0 C for almost four months, reasonably temperate, between 10 to 15 0 C winter climate for four months. To maintain acceptable indoor humidity and IAQ, dehumidification of indoor air is compulsory during 4 to 6 months.
Conventional Air handling units require tight buildings which are totally isolated from the favorable ambient conditions. These AHUs treat all seasons as humid and keep on wasting energy by over cooling, even when the ambient enthalpy may be lower than space enthalpy.
Following points illustrate the present environment:
1. All residential, commercial and IT buildings in UAE without exception are being constructed as tight buildings. Conventional AHU has no option for Ambient Building Connectivity.
2. Due to high internal sensible heat loads, many such buildings require air conditioning, even when the ambient temperature is below the desired indoor temperature.
3. Conventional AHUs can only re-circulate the air so the chiller must operate and keep on over cooling to remove the non existent room heat.
4. There is no provision to facilitate free cooling whenever the ambient conditions are favorable. Use of chiller can be significantly reduced or totally eliminated if the building could make use of favorable ambient conditions.
6. Tight buildings and conventional air handling units loose the free cooling advantage for a range of 3000-4000 hours annually.
7. Opportunity to reduce chiller operating time by 50 to 60% is lost and so are the resultant Opex and Energy Savings opportunities.
So, with conventional AHUs, free cooling is the first casualty. The Chiller must be continuously on and often run on part load to remove the small internal heat load, all the time. Hence, no matter how efficient or reliable a chiller may be, the overall energy efficiency of the system remains poor.
Even today, conventional air handling units are being specified and installed with full knowledge of these disadvantages.
Reasons could be as under:
• “Business as Usual” is the easiest option chosen by all stake holders
• No alternatives being offered by conventional AHU manufacturers
• Few HVAC consultants are exposed to Hybrid Air Handling units
• Energy Managers / Energy Auditors are concentrating on improving the existing installation
with VFD driven fans / better controls and have limited participation in new projects and latest technological innovations
• Efforts are required to make Facility owners / Architects sensitive to energy efficiency and new technologies
Dual Path Technology
May 2002, ASHRAE journal published an article by Mr. Mukesh Khattar, a distinguished ASHRAE member and Energy Director at Oracle on dual path strategy to save energy in HVAC installations.
The core idea was to treat sensible and latent loads independently.
We took this thinking forward and designed Hybrid Air Handling units based on Dual Path technology to treat these loads independently but also use the most cost effective and refrigerant free technology (recycling condensate) using just 10 watts/TR for removing sensible heat instead of
Latent heat and residual sensible heat requires less than 700 watts / TR during peak load conditions.
That is whopping 50% less energy use, 50% less GHG and Ozone-depleting chemical refrigerant emissions, to save us from global warming and climate change, thereby reducing the carbon footprint.
During low load / Free cooling conditions, the power use may drop to as low as 300 to 400 Watts /TR.
Dual Path technology saves a massive amount of energy in the UAE specific application of Treating Fresh Air for desired IAQ. Presently used Fresh Air Handling Units / Heat Recovery Unit are energy guzzlers and need to be retrofitted with energy efficient Dual Path Systems.
More common are the following types of systems:
1. Fresh Air Handling Units
These are vanilla units having a fan pushing hot and humid outdoor air into the AHU room or Fan Filter unit fitted with a 6 or 8 row Chilled water coil sending treated fresh air into the AHU room. In both these cases, power penalty is whooping 12 to 15 kW for just a 1000 CFM unit.
2. Heat Recovery wheel based DOAS
Heat recovery wheels are designed for winter heat recovery in cold climates, where the dust and absolute moisture content are extremely low. These unit are available as Sensible or Energy wheels for sensible or total heat recovery. However, when used in tropical climates in Asia, these units fail to perform after few months due to high ambient humidity and dust loading. Cross contamination, Seal leakages, Drive belt failures, Transmission losses and poor regulation of “demand control ventilation” due to belt driven fans.
Toro Dual Path Fresh Air Handling Units
Let us compare the conventional FAHU / HRU with Dual Path Technology based Toro FAHU /
Toro Units have no moving parts for Heat / Energy recovery and the only moving parts are the backward curve, Electronically commutated direct driven, external rotor motor mounted fans. These
are high efficiency failsafe air movers guaranteed for 40000 operating hours. Nearly 85% sensible
heat is removed from the fresh air by evaporating the recycled condensate in the Twin Heat
exchanger working in Tandem and residual sensible and latent heat is removed by refrigeration
Annual energy savings achieved are 30-50% depending upon the ambient conditions. Finally, a new
generation of Toro Hybrid Air Handling units, based on Dual Path technology offer the opportunity to the HVAC professionals to improve energy efficiency of the entire air-conditioning system. Toro
Hybrid systems, allows design engineers to make full use of free cooling and reduces the chiller
load and operating hours to save energy.
The unique design also permits use of higher temperature chilled water for cooling indoor recirculated air because there is no need to over cool as there is no moisture to remove any more.
Toro Dual Path Unit has already dehumidified the fresh air to the desired room dew point. This
high water temperature operation reduces the chiller load by 30% or more.
Overall annualized energy savings exceed 50% almost anywhere on the planet!