Field Monitoring of Air Conditioning Systems in the Tertiary Sector: Experiences in Italy
Marco Masoero – Politecnico di Torino
CASE STUDIES OF AC SYSTEM ENERGY AUDIT
One of the goals of the AUDITAC project has been to collect
and organise into a data base successful Case Studies of
AC system energy AUDITS
The available information on such audits has proved to be
limited in all participating countries, particularly as far as the
actual energy consumption data are concerned
PROBLEMS ENCOUNTERED (1)
The main energy input for AC systems is the electricity used by the
motors that drive refrigerating compressors, fans, and pumps
Generally, electrical energy is centrally metered at the grid interface
(main delivery board) without separating the individual users (i.e.,
lighting, appliances, AC, etc.)
Most energy service contracts include AC systems, but electricity bills
are generally paid directly by the building owner / tenant
Consequently, no real reasons exist at present for implementing a costly
and relatively complex procedure of gathering disaggregated
electricity use data
PROBLEMS ENCOUNTERED (2)
Most AC system retrofits carried out in the past (at least in
Italy) were determined by reasons different from energy
conservation, namely:
• Improving the comfort condition in work spaces
• Solving IAQ problems, or complying with compulsory
regulations on air changes (e.g. in hospitals)
• Replacing room air conditioners with a central HVAC
system to overcome maintenance problems and to avoid
excessive differences in indoor environmental conditions
PROBLEMS ENCOUNTERED (3)
For space heating, the Heating Degree-Day (HDD) method
has been firmly established since decades as a simple
and reliable means for correlating energy consumption
and local climate
Standard methods for AC energy data analysis are not as
well known and established in the professional community
CASE STUDIES FOR ITALY
Three case studies are presented:
1. Hospital in NE Italy: air conditioning of a surgery / nursing
department
2. Hospital in NW Italy: retrofits of existing refrigeration
equipment
3. Water-to-water heat pump system for a small Auditorium
CASE STUDY No. 1
Surgery / nursing department:
•Air-conditioned floor area 350 m2
•Two identical AHUs each with:
•9700 m3/h air supply (100% outdoor)
•8800 m3/h extraction
•Fan power: 11 kW supply, 4 kW extract
•Intermediate-fluid heat recovery
The energy analysis has been focused on optimising the operation of the
Air Handling Units
Monitoring campaign data (June-September 2006):
•Electricity consumption of the heat recovery loop circulation pump
•Air and water temperatures (16 sensors)
Heat Recovery data analysis:
•Measured average effectiveness of the existing recovery system: 58% (A)
•Estimated effectiveness of an air-to-air recovery system: 65% (B)
Heat recovery type
Δ (B–A)
A
B
Recovered thermal energy (kWh)
2955
7819
4864
Chiller electrical energy savings (kWh)
1477
3910
2433
Pump electrical consumption (kWh)
389
0
-389
Net electrical energy savings (kWh)
1088
3910
2822
•Seasonal savings with existing recovery system: 300 € (A)
•Seasonal savings with air-to-air recovery system: 500 € (B)
Free cooling with outdoor air:
•Free cooling by direct supply of outdoor air (without mechanical cooling) is
assumed feasible when Tout < 20°C
•Estimated energy savings
Free cooling
Cooling energy (kWh)
YES
NO
Δ
Δ(%)
48075 57079
9004
16%
Chiller electrical energy (kWh) 24037 28539
4502
16%
CASE STUDY No. 2
Retrofits of existing refrigeration equipment :
•No cooling foreseen at time of hospital
construction (early 1960s)
•15 chillers installed were needed
•Retrofit work includes:
•New water loop connecting the units
•Two new chillers (963 kW cooling each)
Several different strategies of refrigeration units management (including
recovery of condensation heat) have been analysed
Partial replacement of existing chillers with the new ones
Euro/Day
Daily cost for electric energy and possible saving in the analyzed
period
€ 440
€ 390
€ 340
€ 290
€ 240
€ 190
€ 140
€ 90
€ 40
Obtained saving
Old chillers
os
t
Av
era
ge
C
Oc
tob
er
Se
pte
mb
er
16
-30
Se
pte
mb
er
1-1
5
Au
gu
st
16
-30
Au
gu
st
1-1
5
Ju
ly
Ju
ne
Ma
y
Ap
ri l
-€ 10
New chillers
Recovery of condensation heat for SHW production:
Economic analysis (Net Present Value)
NPV
€ 6.000
€ 4.000
€ 2.000
€0
-€ 2.000
-€ 4.000
-€ 6.000
-€ 8.000
-€ 10.000
-€ 12.000
-€ 14.000
-€ 16.000
0
1
2
3
4
5
6
Years
CASE STUDY No. 3
Monitoring of a water-to water heat pump for a
small Auditorium:
•Air-conditioned floor area 300 m2
•Fan-coil + primary air (3200 m3/h) HVAC
•Heat Pump cooling power 68 kW @ 7-12°C
•Heat Pump heating power 60 kW @ 40-45°C
•Heat source / sink: lake water
Heat Pump / HVAC System Scheme
AHU
SECONDARY
CIRCUIT
FAN COIL
PRIMARY CIRCUIT
HEAT PUMP
TO
LAKE
FROM
LAKE
BEMS
Monthly average Heat Pump C.O.P. vs. outdoor temperature
Monthly average C.O.P.
4,5
4,0
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
30
25
20
15
10
5
0
May
June
July
C.O.P.
August
Outdoor temperature
September
[ °C ]
Supplied energy
Cooling energy vs. air temperature, air specific humidity and air enthalpy
190
Supplied energy
[ kJ / m^3 ]
210
[ kJ / m^3]
190
170
150
130
170
150
130
110
110
90
90
20
21
22
23
24
25
26
27
28
29
30
7
9
11
13
15
Curva cumulativa del fattore di carico giornaliero
Specific humidity [ kg H2O / kg AIR ]
0,0
0,1
Outdoor temperature [°C]
Supplied energy
120
190
100
[ kJ / m^3 ]
170
80
150
[%] 60
130
40
110
20
90
0
35
40
45
50
55
Outdoor air enthalpy [kJ/Kg]
60
65
0,2
0,3
0,4
Utilization factor
0,5
0,6
0,7
Conclusions (1)
The implementation of EPBD’s article 9 may offer a unique
opportunity to promote effective energy savings policies in
building air conditioning
In order to transform this opportunity into a real market,
several technical and institutional barriers still have to be
overcome:
• National legislations must provide clear guidance on AC
inspection, in terms of timing, methodologies, reference
standards, official inspecting bodies , etc.
• Incentives should be adopted in order to promote energy
service contracts including clauses that – similarly to what
is already customary in space heating – remunerate
electrical energy savings in summer air conditioning
Conclusions (2)
• Technical standards, accepted by the professional and
scientific community, are needed both for the calculation of
summer AC energy and for the evaluation of ECOs
• Provisions for disaggregated electricity use metering
should become customary in new installations and
incentives for retrofitting the existing one should also be
introduced
To overcome these barriers, a concerted action will be
necessary in the coming years involving, at the Community
level, more EC funded research and CEN activities, and, at
the National level, an effort to complete the implementation
of the EPBD to include summer air conditioning.