There is a lot of talk around sustainability and improved building practices. The pressure from the public, regulators and building owners is shaping the way buildings are designed, their function within society and their impact on the environment. Many believe that Zero Net Energy (ZNE) is the future and across the U.S, Europe and Asia are targeting ZNE certification.
A popular strategy to get to ZNE is to separate the building’s heating and cooling from the ventilation and dehumidification. Architects and owners are striving to meet heating, ventilation and air conditioning (HVAC) loads with optimum comfort and minimal energy.
Radiant systems provide heating and cooling through pipes, most commonly filled with water, while ventilation and any humidity control requirements are efficiently met by a Dedicated Outdoor Air System (DOAS).
Air & Water Cooling System
Air and water cooling systems take a hybrid approach to cooling using a Dedicated Outdoor Air System for ventilation and dehumidification while radiant cooling uses water to address the sensible heat.
DOAS, as the name suggests, delivers and conditions only the outdoor ventilation air being supplied to the building. By separating the supplying and conditioning of ventilation air from the system that is responsible for handling the rest of the buildings cooling load, the ventilation air can be delivered in more accurate quantities and with more precision to the correct zones within the building. This increase in efficient airflow aids the reduction of excess ventilation needed to comply with ASHRAE Standard 62.1-2010.
Additionally, these dedicated duty systems are very effective at regulating the environmental conditions necessary for controlling microbial population, hydrolysis, swelling in hygroscopic materials, and in promoting respiratory and thermal comfort.
The air and water system is particularly useful in most commercial spaces where the air distribution system can fulfil the ventilation requirements, cover latent loads and remove moisture from the space. The remaining cooling loads are only sensible. Radiant cooling panels or chilled beams can effectively handle sensible loads at temperatures that remain above the dew point, in effect increase the efficiency of the overall cooling system.
Energy Efficient Cooling
The Exploratorium museum, in San Francisco, achieved a LEED Gold certification with the help of a combines DOAS and radiant cooling solution. The museum is also the largest net zero energy museum in the United States. The Exploratorium, surpasses the ASHRAE Standard 90.1-2010 by being a staggering 57% more efficient that is required. One main contributing factor is that the radiant cooling system uses water directly from the Bay. This efficiency, according to Joseph Wenisch, project manager for Integral Group, the lead engineering and systems design company for the project, results in a 94% saving in electrical consumption for cooling and 55% for heating.
The DOAS used in the building has led to further efficiencies by exceeding the minimum ventilation requirements by 30% as set out by ASHRAE. Relative to an all-air variable air volume (VAV) system, the Exploratorium required 50% less ductwork due to the fact that the building used separate systems for ventilation and cooling.
Another great proponent of air and water systems is the Infosys office, Software Development Building (SDB1), in Hyderabad, India. SDB1, is perhaps the ultimate comparison between the hybrid setup of radiant cooling and DOAS against a VAV system. The building is split in two, where 125 000 sf was equipped with the standard VAV system while the remaining half was equipped with DOAS and radiant cooling slabs. InfoSys reports that during its first year of occupancy the radiant and DOAS system used 34% less energy than the VAV system. In years 2 and 3 that energy saving increased to 42% and received higher occupant satisfaction scores.
Radiant Cooling + DOAS Work
Radiant systems have no shortage of myths surrounding them, a few of which have been address in a previous article. One irrefutable fact about radiant is that as a technology it is an enabler, specifically when dealing with cooling systems. It enables the preferred separation of thermal comfort from ventilation. More simply put, its allows architects and builders to specify the use of 100% dedicated ducts for the DOAS which in turn results in better dehumidification, more efficient ventilation and requires less ducting.
Here’s why a radiant cooling system combined with a dedicated outdoor air system is a good idea:
- Reduces air movement and increases comfort
- Improves indoor air quality
- Uses less energy during peak times
- Improves space utilization, reduces building costs
- Reduces initial and operation costs