Full
load efficiency of FOCS and FOCS-CA units
Part
load efficiency of FOCS and FOCS-CA units – Analysis performed by
comparing the IPLV and ESEER indices
Part
load efficiency of FOCS and FOCS-CA units – Analysis performed by
estimating annual power consumption according to the climate in the place
of installation
Part load efficiency
of FOCS and FOCS-CA units – Analysis performed by estimating annual
power consumption according to the climate in different places of installation
Full
load efficiency of FOCS and FOCS-CA units The
FOCS and FOCS-CA units use the new screw compressors optimised for R134A.
The outstanding efficiency of these compressors, together with the accurate
design of the condensing and evaporating section, boost unit performance
and obtain elevated EER values.

Fig. 1 Total EER of FOCS-CA and FOCS units according to cooling capacity
As of today,
FOCS-CA, with EER>3.1 for all sizes, is the only air-chilled liquid
chiller to belong to energy efficiency “class A”, according
to the standards proposed by EECCAC, the “Energy Efficiency and
Certification of Central Air Conditioners” work programme promoted
by the European Community (see Tab. 1).
For the FOCS units, energy efficiency always remains between 2.7 and 3.1.
Tab.1
Energy labelling (EECCAC proposal - Energy Efficiency and Certification
of Central Air Conditioners) for air-cooled chillers according to EER
values.
|
Limit
EER values |
A |
EER>3,1 |
B |
2,9<EER<3,1 |
C |
2,7<EER<2,9 |
D |
2,5<EER<2,7 |
E |
2,3<EER<2,5 |
F |
2,1<EER<2,3 |
G |
EER<2,1 |

Part
load efficiency of FOCS and FOCS-CA units – Analysis performed by
comparing the IPLV and ESEER indices
Increasingly closer attention is being paid towards the power consumption
of air-conditioning equipment.
The EER energy
indices, calculated at rated full load conditions, are certainly an essential
initial parameter for valuating the efficiency of the unit and, in particular,
for making a preliminary comparison between different chillers.
Given that they refer to rated full load conditions, the EER indices do
not consider the behaviour of the unit when works at part loads.
Chillers for air-conditioning, in fact, are mainly used with external
air temperatures that are lower than rated values as well as at reduced
load conditions when the separation stages of the cooling compressors
are used.
This takes into account the fact that, in most conditioning systems, the
lower the external air temperature is, the lower the ambient load gets.
This is due both to the reduced amount of heat transmitted through the
walls of buildings and to the reduced amount of cooling power required
to treat the intake air.
These considerations lead to a more attentive choice of the unit and closer
attention to part load efficiency, with evident economic advantages that
will effect the initial purchase price, the cost of the system and running
costs, and therefore the Total Cost of Ownership which is the sum of the
costs over the entire lifetime of the product.
The market
tends to consider large semi-hermetic compressors as unsuitable for working
at part load conditions.
For this reason, great attention has been focused on multi-circuit units
with more than one scroll compressor per circuit.
Scroll compressors in themselves are considered to be very efficient;
the reduction in the cooling capacity obtained by turning individual compressors
on and off allows system requirements to be tracked very precisely as
one or more compressors working at full load are available for each step.
With this construction typology, it is essential to use leading-edge control
units in order to optimise compressor operation by preventing them from
stopping and starting too often and balancing their operating hours (FIFO
function).
In part load and separated operating conditions, the reduction in power
draw is greater than the reduction in power output, thanks to the oversized
exchangers (condenser and evaporator) which are large enough to handle
maximum refrigerant flow. The increase in the relationship between exchange
surface and quantity of refrigerant boosts energy efficiency.
In the presentation
of the new screw compressors optimised for R134a we saw how their full
load efficiency is greater than that of R407C scroll compressors.
As regards behaviour at part loads, we also pointed out that these new
screw compressors are fitted with an extremely efficient power adjuster
working in either the infinite or four step modes.
The units fitted with screw compressors that can modulate power according
to real load conditions obtain results that are higher than any system
based on switching on and off individual compressors. Of course, this
does not change the fact that the separation of screw compressors using
a slide valve causes inefficiency but, as we will see later, these will
never get near to neutralising the increased efficiency of the system.
Some considerations must also be made as regards construction and reliability.
In a hypothetical mono-circuit system with two compressors for each circuit,
when one of the two compressors is switched off, power is reduced by 50%.
This leads to an marked decrease in condensation temperature and an increase
in evaporation temperature, with evident energy benefits. In units featuring
these characteristics, great attention must be paid to variations: a sharp
decrease in condensation temperature causes the liquid refrigerant, already
at a higher temperature, to partially evaporate (formation of flash-gas
in the liquid line). As a consequence, adjustment disturbances in the
expansion valve feeding the evaporator occur. Similarly, switching on
a compressor (rapid doubling of power) leads to strong oscillations in
the adjustment circuit. This is often associated with insufficient overheating.
These effects must be carefully valuated and controlled. For these reasons,
Climaveneta has always paid the greatest attention to the accurate design
and testing of multiscroll units.
To compare
the real part load efficiency of a unit fitted with R134a screw compressors
against that of a multiscroll R407C unit, we considered two types of chiller
that were configured in order to give approximately the same cooling power
in rated conditions: about 660 kW with air at 35°C and water at 12-7°C.
The first chiller is a FOCS-CA 2712/B. At rated conditions, the unit provides
a cooling capacity of 666 kW, with a compressor power draw of 190 kW and
a total power draw of 208 kW. The unit is fitted with:
- 2 screw
compressors designed for R134a applied to two separate cooling circuits;
- 1 direct expansion shell and tube evaporator with a dual cooling circuit
and a single water circuit. Two asymmetrical passages on the coolant side
optimise performance with R134a;
- 4 condenser coils;
- 12 six-pole fans with a diameter of 800 mm;
- R134a refrigerant.
For the second
unit we took a chiller fitted with:
- 10 rated
25 Hp scroll compressors designed for R407C fitted to 4 cooling circuits;
two circuits each with 3 compressors in parallel and two circuits each
with 2 compressors in parallel;
- 2 large-size plate exchangers for R407C with an overall heat exchange
efficiency superior to that of a shell and tube exchanger (T evap. Scroll
> T evap. Screw);
- 8 generously sized condensing coils with an identical overall exchange
surface to that of the chiller with two screw compressors;
- 12 six-pole fans with a diameter of 800 mm;
- R407C refrigerant.
Calculations
gave the following results:
Unit with
screw compressor FOCS-CA 2712/B:
Cooling capacity 666 kW
Total power draw 208 kW
EER 3.20
Unit with
10 scroll compressors
Cooling capacity 662 kW
Total power draw 264 kW
EER 2.51
At full load,
the FOCS-CA 2712/B unit therefore features a total EER efficiency of 3.20
against 2.51 for the R407C multiscroll unit.
To compare
the efficiency of the two systems, we can calculate the European IPLV
index (called IPLVe for short) and the ESEER index. For a detailed description
of the meaning of these indices and how to calculate them, please consult
the energy index presentation.
These indices are calculated by evaluating the EER of the two units in
75%, 50% and 25% part load conditions, assuming that the external air
temperature at these conditions is 30°C, 25°C and 20°C respectively.
Load |
% |
100% |
75% |
50% |
25% |
Air
temp. |
°C |
35 |
30 |
25 |
20 |
Type of
chiller |
|
Scroll |
FOCS-CA
2712/B |
D% |
Scroll |
FOCS-CA
2712/B |
D% |
Scroll |
FOCS-CA
2712/B |
D% |
Scroll |
FOCS-CA
2712/B |
D% |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Cooling
Capacity
|
kW |
662 |
666 |
+0,006% |
497 |
500
|
+0,006% |
331 |
333 |
+0,006% |
166 |
167 |
+0,006% |
Compr.
power draw |
kW |
229 |
190 |
-17,0% |
136 |
118
|
-13,2% |
70,7 |
66 |
-0,07% |
28,8 |
31,1 |
+7,99% |
Total
power draw |
kW |
264 |
208 |
-21,2% |
155 |
131
|
-15,5% |
83,3 |
74,7 |
-10,3% |
35,1 |
35,5 |
+0,01% |
|
kW |
2,51 |
3,20 |
+27,5% |
3,21 |
3,81
|
+18,7% |
3,98 |
4,46 |
+12,1% |
4,69 |
4,69 |
-0,006% |
Tab.2:
chiller performance at part loads, FOCS-CA 2712/B with screw compressors
optimised for R134a and multiscroll with ten R407C compressors:
At full load conditions, the FOCS-CA 2712/B unit with two screw compressors
optimised for R134a is much more efficient than the same unit with 10
scroll compressors optimised for R407C (+27.5%).
As the load decreases, the efficiency of the multiscroll unit tends to
get closer to that of the FOCS-CA unit optimised for R134a , approx. arriving
at the same value for 25% part load condition.
Using the
data from Tab.2 in the formulas for calculating IPLVe and ESEER, we obtain
the values shown in Tab.3.
It can be seen that the percentage variations between the ESEER and IPLVe
indices are not particular high, +10.6 % and +11.7 % respectively in favour
of the chiller with two screw compressors optimised for R134a.
CHILLER
TYPE |
SCROLLR407C |
FOCS-CA |
SCREW/SCROLL |
ESEER |
3,85 |
4,26 |
10,6% |
IPLVe |
3,75 |
4,19 |
11,7% |
Tab.3:
IPLVe and ESEER comparison between a FOCS-CA 2712/B optimised for R134a
and a chiller with 10 scroll compressors optimised for R407C:
If we suppose a seasonal demand for cooling power of 396,288 kWh (see
following paragraph for calculation method), we can estimate the total
power draw of the two chillers, both when using the IPLVe indicate and
when using the ESEER index (tab. 4)
The total power draw is calculated as follows:
Power draw = Power demand (summer) / Index of efficiency at integrated
part load
CHILLER
TYPE |
SCROLLR407C |
FOCS-CA
R134a |
SCREW/SCROLL |
Seasonal
cooling power |
396.288 |
396.288 |
|
ESEER |
3,85 |
4,26 |
|
Total
power draw (ESEER)
|
102.932
kWh |
93.025
kWh |
-9,62
% |
IPLV |
3,75 |
4,19 |
|
Total
power draw (IPLVe) |
105.677
kWh |
94.579
kWh |
-10,5
% |
Tab.4: comparison of total power draw of a FOCS-CA 2712/B
with R134a and a 10 scroll chiller with R407C assuming a seasonal demand
for cooling power of 396,288 kWh.
The
difference in annual power consumption is 9,907 kWh, a reduction of 9.62%
in favour of the FOCS-CA chiller optimised for R134a using the ESEER index
as the valuation parameter, while the difference is 11,098 kWh, equal
to 10.5%, if the IPLVe index is used.
Supposing electricity costs 0.13 euros/kWh, the annual saving is 0.13
X 9,907 = 1,288 euros/year if calculated according to the ESEER index
and 0.13 X 11,098 = 1,442 euros/year if calculated according to the IPLVe
index.
Part
load efficiency of FOCS and FOCS-CA units – Analysis performed by
estimating annual power consumption according to the climate in the place
of installation
We will now estimate annual power consumption for the
two chillers, assuming:
- installation in a typical central Italian town. We will take Perugia
as an example;
- evaporator inlet/outlet water temperature: 12 / 7°C;
- a linearly variable load demand starting from a maximum of slightly
below the cooling capacity of each of the two chillers with an external
air temperature of 35°C (640 kW) to a minimum of 0 kW with an external
air temperature of 15°C.
This is an acceptable estimate for residential air-conditioning
installations in the Mediterranean area, where a total load is supposed
to be proportional to external air temperature and therefore to the transmission
loads for the introduction of fresh air.
The values of this power consumption analysis for with
the external climate of Perugia are shown in tables 5) and 6).
Tab.5 FOCS-CA 2712/B – time zone 8-18 – Perugia.
External
air
temperature |
Demand |
External
air temperature distribution |
tot
EER |
Total
power draw |
Electricity
draw |
Cooling power
delivered |
°C |
KW |
hours/year |
kW/kW |
KW |
kWh |
KWh |
A |
B |
C |
D |
E=B/D |
F=E*C |
G=B*C |
15 |
0 |
325 |
0 |
0 |
0 |
0 |
17 |
64 |
288 |
5,39 |
11,9 |
3420 |
18432 |
19 |
128 |
269 |
5,14 |
24,9 |
6695 |
34432 |
21 |
192 |
292 |
4,90 |
39,2 |
11445 |
56064 |
23 |
256 |
292 |
4,66 |
54,9 |
16031 |
74752 |
25 |
320 |
258 |
4,46 |
71,7 |
18511 |
82560 |
27 |
384 |
129 |
4,15 |
92,4 |
11924 |
49536 |
29 |
448 |
80 |
3,88 |
115,4 |
9235 |
35840 |
31 |
512 |
44 |
3,61 |
141,9 |
6244 |
22528 |
33 |
576 |
34 |
3,34 |
172,2 |
5856 |
19584 |
35 |
640 |
4 |
3,20 |
200,0 |
800 |
2560 |
|
TOTALE |
2015 |
|
|
90161 |
396288 |
Tab.6
10-scroll unit for R407C – time zone 8-18 – Perugia
External
air temperature |
Demand |
External
air temperature distribution |
tot EER |
Total power
draw |
Electricity
draw |
Cooling
power delivered |
°C |
KW |
ore/anno |
kW/kW |
KW |
kWh |
KWh |
A |
B |
C |
D |
E=B/D |
F=E*C |
G=B*C |
15 |
0 |
325 |
0 |
0 |
0 |
0 |
17 |
64 |
288 |
5,21 |
12,3 |
3540 |
18432 |
19 |
128 |
269 |
4,91 |
26.0 |
7007 |
34432 |
21 |
192 |
292 |
4,61 |
41,6 |
12157 |
56064 |
23 |
256 |
292 |
4,32 |
59,3 |
17309 |
74752 |
25 |
320 |
258 |
3,98 |
80,4 |
20744 |
82560 |
27 |
384 |
129 |
3,71 |
103,4 |
13338 |
49536 |
29 |
448 |
80 |
3,40 |
131,7 |
10535 |
35840 |
31 |
512 |
44 |
3,10 |
165,2 |
7268 |
22528 |
33 |
576 |
34 |
2,82 |
204,5 |
6954 |
19584 |
35 |
640 |
4 |
2,51 |
255,0 |
1020 |
2560 |
|
TOTALE |
2015 |
|
|
99872 |
396288 |
The comparison between annual power consumption of the two different chillers
is summarised in fig. 3

The comparison
between annual power consumption of the two different chillers is summarised
in fig. 3
From tables 5) and 6) we can deduce the annual power consumption of the
two chillers:
- FOCS-CA
2712/B chiller with R134a: 90161 kWh
- chiller with ten scroll compressors optimised for R407C: 99872 kWh
The difference in annual power consumption is 9,711 kWh, amounting to
9.7%, in favour of the FOCS-CA 2712/B chiller with two screw compressors
running on R134a.
Assuming the cost of electricity to be 0.13 euro/kWh, the annual saving
amounts to = 0.13 X 9,711 = 1,262 euros/year.
It should
be pointed out that, at the same seasonal cooling demand, the difference
in the total power draw of the two chillers, calculated according to the
climate in the place of installation, practically coincides with the value
calculated using the IPLVe index and, in particular, the ESEER index.
This shows how the use of these indices offers an extremely rapid and
reliable valuation of the power consumption of cooling units as it also
considers part load operation.
CHILLER
TYPE |
SCROLLR407C |
FOCS-CAR134a |
Seasonal
cooling power |
396.288 |
396.288 |
Total
power draw (calculated) |
99872
kWh |
90161
kWh |
ESEER |
3,85 |
4,26 |
Total
power draw (ESEER) |
102.932
kWh |
93.025
kWh |
IPLV |
3,75 |
4,19 |
Total
power draw (IPLVe) |
105.677
kWh |
94.579
kWh |
The IPLVe
or ESEER indices therefore allow us to calculate the seasonal electricity
draw and compare various chillers, bearing in mind the differences in
their part load performance.
Part
load efficiency of FOCS and FOCS-CA units – Analysis performed by
estimating annual power consumption according to the climate in different
places of installation
Similar evaluations to
the above have been made, considering the two different chillers and always
using a linearly variable load, with climate figures relative to round-the-clock
operation in various European cities.
|
Tipo
Chiller |
|
10
Scroll R407C |
FOCS
2712/B R134a |
|
Absorption
kWh/year |
Absorption
kWh/year |
Saving
kWh/year |
Saving
% |
|
Perugia |
152.801 |
138.967 |
13.834 |
-9,05% |
Milano |
138.738 |
126.580 |
12.158 |
-8,76% |
Francoforte |
86.420 |
79.306 |
7.114 |
-8,23% |
Parigi |
76.557 |
70.573 |
5.984 |
-7,82% |
Londra |
50.337 |
46.920 |
3.417 |
-6,79% |
Table
7 Summary of annual power consumption in various European cities.
In this case,
power consumption was not evaluated by applying the ESEER or IPLV indices,
but considering the effective performance of the unit over an operating
period of one year.
The advantage
of the chiller with screw compressor running on R134a compared with the
multiscroll varies according to the climate conditions relative to various
European cities. The advantage, ranging between 6.79% and 9.05% decreases
as we pass from the Italian climate to the central/northern European climate
because, maintaining the same comparison criterion (maximum load at an
external temperature of 35°C and no load with external air at 15°C),
part load operation becomes more important. In this condition, the EER
of the multiscroll tends to reduce the advantage of the screw compressors.
In all cases, power consumption of the chiller with screw compressors
running on R134a is always significantly lower than that of the chiller
with 10 scroll compressors running on R407C.
Climaveneta
S.p.A
|