| Radiant System Vs Forced Air System |
| There are three basic forms of energy. |
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| Radiant Heat |
| Radiant heat transmits heat through space/air in all directions from a body with more energy to a body with less energy. If one object is warmer than another, the cooler object will absorb heat radiated from the warmer object, cooling one and warming the other. The sun is a perfect example of radiant heat exchange: the radiant heat wave travels through cold space until it hits a surface and warming it. This is why people and objects feel much warmer when exposed to the sun than when they are shaded. Air is heated very little by radiant energy. |
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| Conduction |
| Conduction is heat transfer between two bodies in actual physical contact with each other. |
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| Convection |
| Convection is heat transfer between moving fluid (water, air) and a solid body or another fluid. |
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| Radiant Systems |
| The cooling and heating medium for radiant systems is typically water that may be conditioned by boilers, heat pumps, chillers, geothermal ground loops, solar thermal panels, etc. There are many advantages to radiant systems over forced air systems, these include: |
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| Energy savings |
Exchanges heat with water rather than air. Water is a better heating and cooling transport agent than air. Air requires a much larger volume (1000 times more) to transport the same amount of heating and cooling capacity. Water uses 30% less energy by reducing 75% motor HP than forced air systems. The system is self regulated based on the room load. If the room is empty, no energy transfer happens, thus saving energy.
There have been a few studies on the energy savings created by capillary mats. International Energy Studies have performed test of Hydraulic Radiant Cooling in a high-rise office building in Oakland, California which demonstrate some of the cost savings associated with this technology. The Lawrence National Laboratory also has performed studies of the energy savings of hydraulic radiant cooling systems. |
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| Space saving |
| Low floor to floor height requirements due to small ductwork, air conditioning units and fans. Ceiling plenum requires only a very small space due to a reduced supply air capacity. Equipment room size can be reduced, providing additional rentable space. This allows more freedom to design and create usable space. |
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| Noise reduction |
| Noise is reduced because much less fan power is required. The radiant panel and capillary tubes are virtually silent. The only noise is created by a small D.O.A.S. fan and pump. |
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| Human comfort |
| The space is cooled/heated evenly, thus creating an even temperature. Better air quality as it uses 100% outside air. The application of radiant cooling significantly eliminates the contamination associated with re-circulated air, improving indoor air quality and reducing airborne transmitted contaminants. Improved air quality results in a better indoor environment, increasing productivity and health. |
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| Zoning |
| Zoning flexibility is easily available as space can be easily controlled by the opening and closing of the valves depending upon the room thermostat.. |
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| Maintenance |
| Lower maintenance is achieved as there are few electrical devices compared to a forced air system. Sub-stations consist of control valves, dew point sensors, pump and heat exchangers will require some maintenance. DOAS system will require less maintenance due to reduced equipment capacity and the location. |
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| Limitations |
Sensible cooling capacity is 25 btu/sq.ft.
Limited experience by U.S. engineers and architects.
Availability of professionals for design, installation, maintenance and repair of a system |
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| Benefits |
• Saves energy and protects indoor air quality
• 100% outside air is introduced without draft.
• Latent load is controlled by D.O.A.S.
• Can be applied to concrete, plaster/drywall or drop ceiling.
• Can be applied over existing wall ceiling without significant intrusion into space.
• Each room can have a separate zone
• Less energy is required to circulate water than air.
• Reduced noise
• Smaller and less conspicuous air supply ducts.
• No interference with draperies and blinds.
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| Forced air system |
The main function of forced air conditioning system is to cool the air inside the space. In the 1970s, variable-air volume (VAV) system gained prominence mainly because they addressed the period's energy concern. A new technology that has none of their drawbacks, poised to push VAV system into obsolescence, a new HVAC strategy bringing together a D.O.A.S, radiant cooling and heat recovery may soon transform the industry.
For any building envelope, perimeter thermal loads and interior heat generation can be designed to reduce the cooling load below 25 btu/sq. ft. is a candidate for radiant cooling/dedicated outside air system.
For any building envelope, perimeter thermal loads and interior heat generation can be designed to reduce the cooling load below 25 btu/sq. ft. is a candidate for radiant cooling/dedicated outside air system. |
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