Table of Contents
Advertisement
3.4 What is the E.V.I. technology (enhanced vapour injection)
EVI stands for "Economised Vapour Injection." The technology involves injecting refrigerant vapour into the middle of the compression process,
a procedure that significantly boosts capacity and efficiency. Each scroll compressor used in these units is similar to a two-stage compressor
with built-in inter-stage cooling. The process begins when a portion of the condenser liquid is extracted and expanded through an expansion
valve. The low temperature liquid/gas mixture produced is injected into a heat exchanger that operates as a sub cooler. Any liquid is evaporated
and the vapour produced is superheated. The superheated vapour is then injected into an intermediate port in the scroll compressor. This
cold vapour reduces the temperature of the compressed gas thus enabling the compressor to raise the pressure to levels (and temperatures)
beyond that possible with a single stage scroll. The additional sub cooling of the main volume of liquid refrigerant increases the evaporator
capacity. This compressor technology generates a larger pressure ratio between condensing and evaporating pressures, with significant
performance improvement. Using this technology enables the units to produce hot water up to 65°C and the ability to operate down to -20°C
ambient temperature.
P
Pi
The graph below shown the trend of the coefficient of performance C.O.P. compared with a standard scroll compressor (dotted line); EVI
scroll compressor (Continuous curve).
The efficiency of EVI compressors at low ambient conditions is about 25% higher than standard scroll compressors. The effect of this
difference becomes even more evident in applications that require high hot water temperatures (i.e. when domestic hot water is required).
In such applications the operational limits of a standard scroll compressor prevent it from producing the required hot water temperature at
air ambient temperatures below 5°C.
Max Water
Temperature (°C)
The above graph shows the operation range of the EVI scroll compressors supplied in the units; at -20°C ambient the water outlet tempe-
rature is still 52°C; this performance makes the installation of a heat pump suitable for any European condition.
Pm+i
Pi
Pm
Ph
C.O.P.
4,0
3,5
3,0
4,0
2,5
3,5
2,0
3,0
-15
-10
2,5
2,0
-15
-10
70
60
50
70
40
60
50
30
40
20
30
10
-20
20
-10
10
-20
-10
TEV
HX
Water production at 40°C
-5
0
5
Ambient temperature (°C)
-5
0
5
0
10
20
30
0
10
20
30
Ambient temperature (°C)
14
m +i
i
m
TEV
Water production at 40°C
Water production at 55°C
Water production at 55°C
10
15
10
15
40
50
40
50
Rev. A 11-2020
Advertisement
Table of Contents
