ASHRAE Journal - June 2020 - 44

2020

ASHRAE TECHNOLOGY AWARD CASE STUDIES

as IT equipment kW loads reduce from the maximum
design load, the PUE goes up. This is predominantly
due to lower efﬁciencies under part-load operation
of the mechanical cooling systems and associated
compressor performance plus the electrical systems'
inefﬁciencies. However, through ingenuity, the team
has managed to reverse the outcomes at the Kao Data
Campus. Through the application of the Thermal
Guidelines and elimination of mechanical refrigeration, the PUE evidenced during the commissioning
and ﬁnal integrated system test (IST) remained equal
to, or below, the full-load PUE. As the ITE load reduced
the cooling, the system dynamically responded with
the facility input power tracking closer to the ITE input
power, resulting in an optimized PUE and greater overall energy efﬁciency. The system underwent testing
through commissioning levels 1-5, in accordance with
ASHRAE Guideline 1.6P, Commissioning of Data Centers.
The data collected during the various stages of testing, under full- and part-load conditions, enabled the
theoretical design PUE modeling to be veriﬁed and
recorded (Table 1).

Indoor Air Quality and Thermal Comfort

The primary function of a data center is to house and
reliably support compute, storage, and networking
equipment, termed by ASHRAE Technical Committee
9.9 (TC 9.9) as information technology equipment (ITE),
and, as such, thermal comfort and indoor air quality for
human occupation beyond statutory obligations is not
a primary consideration. Data center industry environmental conditions relate to air temperature, humidity
level, and air cleanliness for the ITE, both gaseous and
particulate contamination.
The TC 9.9 thermal guidelines1 internal thermal environments design criteria are as follows:
* Class A1 Recommended: 18°C (64.4°F) -27°C
(80.6°F) DB
* -9.0°C (15.8°F) DP, 60% RH and 15°C (59°F) DP
The Kao Data cooling system is closely controlled to
maintain the internal temperature within this range,
and the only introduction of external air is by an ancillary air-handling system, which provides a nominal
air change rate of 0.5 ach to 1 ach. This positively pressurizes the technical space to prevent dust ingress and
air inﬁltration. This system includes functionality for
humidiﬁcation and de-humidiﬁcation to ensure that
44

ASHRAE JOURNAL

ashrae.org

J U N E 2020

Table 1 Validated PUE through integrated system testing (2.2 MW).
Simulated Thermal IT Load

Measured PUE

100% (2,200 kW [7.51 MBtu/h])

1.21

75% (1,650 kW [5.63 MBtu/h])

1.16

50% (1,100 kW [3.75 MBtu/h])

1.14

25% (550 kW [1.88 MBtu/h])

1.15

the outside air introduced into the technical space
adheres to the guidelines.
Data centers must be maintained to ISO 14644-1 Class
8. Coupled with the correct maintenance program, this
level of cleanliness can generally be achieved by the following ﬁltration levels:
* The recirculated air ﬁltered with MERV 8 ﬁlters (G4/
F5)
* Outside air ﬁltered with MERV 11 (F6) or MERV 13 (F7)
The Kao Data pressurization air-handling system previously mentioned incorporates both MERV 8 pre-ﬁlters
and MERV 13 ﬁlters to ensure particulate cleanliness is
maintained.
In addition, manufacturers of IT equipment require
data center operators to consider exposure to gaseous
contamination to ensure equipment warranties are not
put at risk. Research shows sulphur, chlorine, and ozone
can, in varying compositions, contribute to electronic
component reliability issues and accelerated corrosion.
However, this requirement is lesser known and catered
for across the data center industry. ASHRAE TC 9.9 published guidance on gaseous contamination thresholds,2
referencing ANSI/ISA-71.04-2013, Environmental Conditions
for Process Measurement and Control Systems: Airborne
Contaminants, summarized as reactivity rate thresholds:
* Class: G1; Severity Level: Mild; Copper Reactivity:
<300A (angstroms) per month
* Class: G1; Severity Level: Mild; Silver Reactivity:
<300A (angstroms) per month
To ensure that the indoor air quality remains within
these limits, real-time corrosion monitoring for both
copper and silver reactivity monitors airborne contamination levels in accordance with ISA-71.04.2013, ensuring the customers' equipment warranties are never put
at risk. This is unprecedented for a wholesale co-location
data center in the UK.
https://www.ashrae.org/
ASHRAE Journal - June 2020

Table of Contents for the Digital Edition of ASHRAE Journal - June 2020
