Install Instructions

79
IM-PR 566442 1114 (Design Manual)
3.6 Commercial radiant cooling
Radiant cooling systems operate by reducing
the surface and air temperature within a space,
which is referred to as “sensible cooling.” “Latent
cooling” occurs when the heat content of air is
reduced through condensation of the air’s vapor
on a cool surface. To avoid condensation on
radiant cooled surfaces, latent cooling should be
provided by a supplemental forced-air cooling and/
or dehumidification system. The use of radiant
surfaces for sensible cooling combined with
dedicated outdoor air systems for latent cooling
and ventilation has shown great promise for energy
savings. In fact, an article in the ASHRAE Journal
projected more than 50% savings for a radiant
cooled slab and dedicated outdoor air system
versus a standard constant air volume cooling
system.
17
3.6.1 Design temperatures
Cooling design temperatures are selected as a
function of cooling load, occupant comfort and
dewpoint temperature.
Panel surface temperature: Lower panel surface
temperatures provide higher heat transfer when
cooling a space. However, if surface temperatures
drop below the space dewpoint, undesired
condensation can occur. Another design parameter
that limits the low end of the panel surface
temperature is concern for occupant comfort.
For example, to ensure that comfort levels are
acceptable in occupied rooms, it is advisable to
maintain floor surface temperature at or above
66°F. This temperature is the lowest temperature
that has been shown to achieve a 10% predicted
percentage dissatisfied (PPD) among occupants
(or acceptable comfort for 90% of occupants),
while maximizing heat transfer to the floor.
Based
on considerations for condensation and occupant
comfort, it is advisable to maintain floor temperature
above the higher of the dewpoint and 66°F.
18
17. Doebber, I., M. Moore, M. Deru. 2010. “Radiant Slab Cooling for Retail.” ASHRAE Journal 52(12):28-37.
18. In some cases, facilities have successfully specified floor surface temperatures of 64°F while maintaining acceptable levels of
occupant comfort.
19. Doebber, I., M. Moore, M. Deru. 2010. “Radiant Slab Cooling for Retail.” ASHRAE Journal 52(12):28-37
Standard
Efficiency CAV DX
RTUs
High-Efficiency
VAV DX RTUs
Radiant
Floor-DOAS:
Constant Flow –
Variable Supply
Temperature
(reactive control)
Radiant
Floor-DOAS:
Variable Flow –
Variable Supply
Temperature
(proactive control)
DX and chiller 189,855 125,866 41,365 32,916
Pumps – – 22,728 16,163
Fluid coolers – – 121,302 61,810
Fans 247,914 217,964 78,838 73,240
Total HVAC 437,769 343,830 264,233 184,130
Savings over CAV
baseline (%)
0% 21% 40% 58%
Table 3-6 Modeled HVAC annual electrical energy consumption, based on an example big box retail store in
Sacramento, CA
19