Radiant Cooling System

Radiant Cooling System

In fulfillment,As Part of Submission

for S.B.D.P-I,Pragya Gupta

Introduction

A radiant cooling system refers to a temperature-controlled surface that cools indoor temperatures by removing sensible heat and where more than half of heat transfer occurs through thermal radiation.

-ASHRAE Handbook. HVAC Systems and Equipment. Chapter 6. Panel Heating and Cooling Design. ASHRAE. 2008.

Heat will flow from objects, occupants, equipment and lights in a space to a cooled surface as long as their temperatures are warmer than that of the cooled surface and they are within the line of sight of the cooled surface. The process of radiant exchange has a negligible effect on air temperature, but through the process of convection, the air temperature will be lowered when air comes in contact with the cooled surface

Introduction

The temperature people feel is an average of the air temperature in a room and the radiant temperature from the surrounding surfaces.For Example If the floor temperature is 18°C and the room temperature 26°C people will feel it as 22-24°C.Therefore with floor cooling the room temperature can be increased compared to air conditioning system.

The cooling load is mainly defined by- Internal load Qint- Load from sun radiation Qsun-Convective load QconvThe convective load is proportional to the temperature difference

Tout – Troom

With radiant cooling the room temperature can be reduced which reduces the convective cooling load.

Potential

Energy savingsDemand shifting and reductionImproved thermal comfortImproved indoor air quality

Synergies with UFAD, DV, DOAS, and natural ventilationSynergies with envelopeCost competitiveness

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Potential

To remove 1 kW heat from a room an A/C ducting system needs ~ 140 W for the ventilator.For the same load a radiant cooling system needs ~3 W to run the circulation pump.

Radiant cooling can significant reduce the electricity consumption for cooling up to 40%.

System Design

Radiant Systems: aim to affect the thermal comfort of space occupants by modifying the radiant field within a space

Primary effect can be on surface temperaturesSome systems are simply direct radiant sourcesControls are more complex but inclusion of radiant effects may result in better comfort at lower air temperatures

This is a surface cooling system where the water tubes are placed in the roof slab that absorbs the heat from heat sources in the room.The Slab absorbs the heat and exchanges it with the circulating water. Typically the circulating water only needs to be 2-4°C below the desired indoor air temperature.Once having been absorbed by the actively cooled surface, heat is removed by water flowing through a hydronic circuit, replacing the warmed water with cooler water.

System Types

Chilled Slabs Floor or Ceiling

Cooling delivered through the floor makes the most sense when there is a high amount of solar gains from sun penetration, as the cool floor can more easily remove those loads than the ceiling.However, it is easier to leave ceilings exposed to a room than floors, increasing the effectiveness of thermal mass. Also, greater convective heat exchange occurs through a chilled ceiling as warm air rises, leading to more air coming in contact with the cooled surface.

Schematic Application

Typical Cross Section

Radiant cooling panels are generally attached to ceilings, but can be attached to walls. They are usually suspended from the ceiling, but can also be directly integrated with continuous dropped ceilings.Chilled panels are also better suited to buildings with spaces that have a greater variance in cooling loadsCeiling panels are also very suitable for retrofits as they can be attached to any ceiling.Panels tend to cost more per unit of surface area than chilled slabs.

Ceiling Panels

Slab Radiant Cooling System Using Bore Wells

This system consists of two bore wells and the water is pumped from one bore well to the radiant slab and the hot water that comes out from the radiant slab is connected to another bore well. Using this method it is possible to maintain the slab temperature same as the ground temperature. The idea behind this is that the earth temperature below 12 ft is constant throughout the year and it is the yearly average temperature of a particular geographical location. The room is also ventilated using stack effect ventilation system.

Ceiling Panels

Structural Slab Radiant Cooling System Using Cooling Tower

The radiant slab is connected to the cooling tower to maintain the slab temperature near to the wet bulb temperature (called Wet bulb approach).

This systems cools the space considerably well in hot and dry climates where there is higher difference in dry bulb and wet bulb temperatures. The top floor of the building which is exposed to sun radiates high amount of heat to occupant space can be controlled by using this system.

Ceiling Panels

Maximum comfort Draft free, no noise cooling Lower sensed temperature Lower investment costs Lower energy costs Architectural freedom Minimal maintenance Malfunction free operation Space conditioning equipments is not needed at the outside walls simplifying the wall, space and structural systems. No space is required within the air conditioner for mechanical equipment. Structural slab radiant system can be used for heating and cooling the buildings with same pipes.

Advantages

Sample of Underfloor Cooling Application:Hearst Tower, Manhattan – USA

The 856,000-sq-ft development, which incorporates Hearst’s 1928 landmark headquarters and adds a Norman Foster designed tower, was engineered to use 25% less energy than a building that meets minimum requirements of prevailing codes (ENR 10/31/05 p. 24). Some of the efficiency is in the radiant floor, combined with displacement ventilation.With radiant cooling, the sunlight hits the floor, and heat is taken away by circulating water in the embedded pipes, spaced 9 in. on center. Because the slab never warms up, the solar energy never becomes a load in the space. Radiant cooling takes advantage of the fact that it is more efficient to remove heat from water than to remove it from air.

Case Study

Sample of Underfloor Cooling Application:Zero Energy Office Building Bangi, Malaysia

The building is designed to achieve a building energy index of 40 kwh/m²/yr. The benchmark to qualify as an energy efficient building (as defined in Malaysian Standards MS1525:2001) is energy consumption of not more than 135 kwh/m²/yr.

ZEO achieves 75% of its cooling requirements by radiant cooling – water is piped through the floor slabs to draw off heat during the day, and ambient cooling and evaporation during the night cools the water for use the following day.The remaining 25% of its cooling requirement is achieved by conventional air-conditioners, powered by electricity generated by the BIPV system.

Case Study

Thank You