CASE STUDY on Highly Energy Efficient Treated Fresh Air system
Project Title: Air conditioning of Pressing Hall
Background:
Client name is a leading Electrical and Electronics major of Wo rld. They have a factory in
location which also manufactures Heavy duty Transformers. The core of these transfo rmers
are heated in an oven to 120 deg C for 5 days and then brought out to a hall for Pressing
work for 18 hours. If this activity exceeds 18 hours then the core has to be sent back to Oven
for re-heating. During Pressing activity around 20 workers have to work inside the hall at
high temperature before it is dispatched for further processing. So the conditions have to be
made to suite human comfort levels . The factory has one existing hall which functions at
28±2°C and relative hu midity condition of 58%. This hall had a chilled water based HVAC
system with water coo led condenser.
Company planned to construct a new hall with an air-conditioning system to maintain
temperature 28 ±2°C and relative humidity condition of 55%. Energetic Co nsulting designed
and installed a 80TR Re -circulation system accompanied by a 25TR Treated Fresh air (TFA)
unit. It was recorded that the TFA functioned at 0 .6kW/TR against conventional consumption
of 1kW/TR which saved 40% energy. Additio n of TFA also resulted in better performance of
Re-circulation system reducing its specific energy consumptio n from expected 1.1kW/TR to
0.85kW/TR
Overall Proj ect Sc ope :

Design & Engineering

Preparation of P&I diagram, ducting layout, fabricatio n drawing s

Preparation of Bill of Quantities

Project monitoring & Coordination to maintain the overall project schedule

Project Management Assistance

Commissioning Activity
System specification :

Room dimension
:
15 m X 20 m X 12 m

Room temperature
:
28 °C + 2 °C

Humidity
:
Not more than 55% R H

Room pressure
:
+2 mm WC
P re pa re d b y: En erg e ti c Co ns ul ti ng Pv t. Lt d. – Th an e
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Heat Load details

Product details
:
300MT @ 90°C

Duration
:
18 hrs operation

Other Equipment
:
20kW
(Lighting, motor, Control panel)

Working People
:
20
Probl em situation:
Challenges in designing energy efficient system
Heavy outside air infiltration due to following reasons:
a. Building envelop is co nstructed out of galvanium sheets and there were large gaps
between the sheets and support civil structure.
b. Hall has 5 m x 4 m size two doors which open into another unconditioned space at
least twice in 18 hours span, resulting in heavy disturbance in roo m conditions.
Varying occupancy
a. Workers and other personnel constantly enter and leave the hall leading to
variation in humidity and temperature.
Proposed Solutions:
Design changes included to overcome these challenges
Building envel ope: Insulation and building envelop treatment was introduced to reduce, air
infiltration moisture ingress thro ugh walls and solar heat gain.
Humidity contr ol: Infiltration of outside air and reducing sensible load together have a
drastic impact on humidity resulting in steep humidity rise. Conventional Method of
managing the humidity rise is El ectrical Heaters in AHU with constant air volume circul ation
is highly energy inefficient. Design innovations implemented result in complete elimination
of electrical heaters. The modified design included:

Separ ate high COP Treated fresh Air (TFA) unit :
Specially designed TFA unit with min
COP of 6 for Independent control of fresh air dew point regardless of room dry bulb
temperature and to maintain positive pressure inside the room

Variable air volume circulation by maintaining constant Discharge Air Temperature with
blower speed modulation.

Selection of multiple compress ors of different capacities per AHU to work in tandem with
blower speed variatio n to maintain air to heat load ratio.
P re pa re d b y: En erg e ti c Co ns ul ti ng Pv t. Lt d. – Th an e
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Featur es of the installed s oluti on :

No untreated outside air entering room thereby improving dust and humidity co ntrol

Balanced average positive pressure inside ro om regardless of frequent door openings

Heat ingress reduction from 10 kW to 5 kW by improved building envelope

No electrical heaters installed in AHU for humidity control in spite of sensible heat variation
from 20 to 100%.

No reduction in COP o f total system for 20 to 100% load variatio n.
Recorded Results :
Installation was completed and final performances were measured and verified to compare with
design intent.
Following parameters were included in the M&V protocol for TFA unit:
Parameters
UoM
Proposed
Actual
m 3 /hr
6000
5950
C
33
35
Inlet Air R H
%
80
75
Outlet air Temperature (DBT)
°
C
28±2
14
Outlet Air temperature (DPT)
°
C
14
11
Power Consumption of system
kW
20
16.27
Noise level
dB
60
75
Heat load on the system
TR
25
33
kW/TR
0.8
0.5
Air flow at entry
°
Inlet air temperature (DBT)
Energy Performance o f the system
The addition of separate TFA units lead to better performance of Recirculatio n AHU unit which was recorded as below :
Parameters
Return air dry bulb temperature
(DBT)
Supply air dew point temperature
(DPT)
Supply air dry bulb temperature
(DBT)
Pressure (For air flow) at outlet
Fan Power consumptio n
(15,000 m 3 /hr x 4 No s.)
P re pa re d b y: En erg e ti c Co ns ul ti ng Pv t. Lt d. – Th an e
UoM
Proposed
Actual
°C
28±2
27±2
°C
14
13.2
°C
16
15.2
mmWC
65
40
20.0
20.4
kW
3
Compressor power co nsumption
(20 TR) x 4 Nos.
Pressure in the room
Energy Performance o f the system
kW
88
66.4
mmWC
kW/TR
2
1.1
2
0.85
Summary:
The system installed is designed to take care of fresh air load separately by treating fresh air in
TFA unit . This TFA consumed upto 40% less energy than com parable conventional TFA units.
Individual TFA system gives better control to maintain RH inside the room by treating fresh air and
also reduce the load on the r ecirculation AHU and brings down its specific energy consumptio n
(kW/TR) by 22%.
P re pa re d b y: En erg e ti c Co ns ul ti ng Pv t. Lt d. – Th an e
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