Cooling analysis for Milan appartment

Introduction

This report shows an overview of the cooling performance of the OXYCELL Dew Point Cooler (OXYCELL DPC), the OXYCELL Indirect Evaporative Cooler (OXYCELL IEC), the OXYVAP Direct Evaporative Cooler (OXYVAP) and the OXYVAP Two-stage Cooler (OXYVAP+), compared to conventional air conditioning technology (A/C).

 

To calculate the performance comparison, a fictional space of certain dimensions and heat load has been defined. The performance of each cooling technique has been calculated for one year of climate data.

 

Calculation method and details 

Overview of details and assumptions

Country

Italy

City

Milan

Year

2012

Number of data points

8482

Heat load type

Sensible only

Heat load behaviour

Linearly increasing with outdoor temperature

COP behaviour of conventional A/C

Linearly decreasing with outdoor temperature

Displacement ventilation*

Stratification, according to the 50% rule

Floor surface area

100 m2

Height

3 m

Height of occupied zone

1.8 m

Maximum allowable temperature within the occupied zone**

27.4 °C

Minimum outdoor temperature for cooling

20 °C

Maximum outdoor relative humidity for cooling

90%

Amount of cooling hours

2383 hours/year

Minimum specific heat load

20 W/m2

Maximum specific heat load

40 W/m2

Minimum COP of conventional A/C

2.6

Maximum COP of conventional A/C

4.0

Number of OXYCELL 1000 DPC heat exchangers

2

Number of OXYCELL 1000 IEC heat exchangers

2

Number of OXYVAP 45x55 pads

1

Overall fan efficiency

40%

*Source: Håkon Skistad, Elisabeth Mundt, Peter V. Nielsen, Kim Hagström and Jorma Railio, 2001, Displacement Ventilation in Non-industrial Premises, Rehva – Federation of European Heating and Air-conditioning Associations.

**Adapted from Australian Standard AS 2913-2000.

 

 

 

OXYVAP Direct Evaporative Cooler

The OXYVAP is a direct evaporative cooling pad, that adiabatically cools air towards its wet bulb temperature, typically achieving a 90% saturation efficiency. Having dimensions of HxWxL = 546 mm x 590 mm x 101 mm, it is designed to deliver a supply airflow up to 2500 m3/h.

 

OXYVAP cooling principle OXYVAP application principle
OXYVAP application principle

 

 

OXYVAP Two-stage Cooler

The OXYVAP Two-stage Cooler is an OXYVAP-based cooling configuration, that uses an additional air-to-water heat exchanger to enhance its performance. Chilled water from the OXYVAP is fed to the heat exchanger to pre-cool outdoor air before it enters the OXYVAP pad, that is then fed with heated water returning from the heat exchanger.

 

Since it is a closed system, the cooling process as a whole will be adiabatic, but the combination of the pre-cooling process and the recirculation of water between the components will lead to a vertical temperature gradient in the air leaving the OXYVAP pad.

 

The upper half of the supply air will have a higher enthalpy than the intake air, whereas the lower half will have a lower enthalpy. When the upper half of the air is discarded, the lower half can be used as supply air, reaching an average temperature below the initial wet bulb temperature, while less moisture is added compared to traditional adiabatic cooling.

 

OXYVAP+ application principle

OXYVAP two stage application principle

 

OXYCELL Indirect Evaporative Cooler

The OXYCELL IEC is a counter-flow indirect evaporative heat exchanger in which air in the secondary channel (work air) is adiabatically cooled, hereby extracting heat from air in the primary channel (process air). In practice, primary air cools down to within a degree above the physical limit, i.e. the wet bulb temperature of the secondary inlet air, while maintaining a constant absolute humidity. Having dimensions of HxWxL = 715 mm x 380 mm x 588 mm, it is designed to deliver a supply airflow up to 1000 m3/h.

 

OXYCELL IEC cooling principle OXYCELL IEC application principle
OXYCELL IEC cooling principle OXYCELL IEC application principle

 

 

OXYCELL Dew Point Cooler

The OXYCELL DPC is a counter-flow dew point cooler, in fact a special application of the OXYCELL IEC, in which part of the cooled primary air (typically 35-40%) is branched off and used as secondary inlet air, where it is cooled adiabatically, hereby extracting heat from the primary air stream. Ideally, primary air can be cooled down to its dew point temperature, while maintaining a constant absolute humidity. Having dimensions of HxWxL = 715 mm x 380 mm x 588 mm, it is designed to deliver a supply airflow up to 1000 m3/h.

 

OXYCELL DPC cooling principle OXYCELL DPC application principle
OXYCELL DPC cooling principle OXYCELL DPC application principle

 

 

Climate data

 Psycrometric chart Milan climate data 2012

Milan Climate Data 2012

 

Overview of minimum, average and maximum outdoor conditions

Value

Air pressure

Dry bulb temperature

Wet bulb temperature

Dew point temperature

Relative humidity

Absolute humidity

Specific enthalpy

[mbar]

[°C]

[°C]

[°C]

[%]

[g/kg]

[kJ/kg]

Minimum

986

-17.0

-17.3

-18.9

12.0

0.8

-15.0

Average

1016

14.7

11.1

9.0

72.3

7.1

31.6

Maximum

1035

35.0

23.3

22.1

100.0

16.7

69.1

 

 

 Outdoor temperature

 

Milan outdoor temperature

 

Outdoor humidity

 

Milan absolute humidity

 

 

OXYCELL DPC cooling performance 

  

OXYCELL DPC supply temperature

 

OXYCELL DPC supply temperature

 

 

Outdoor wet bulb temperature

 

Milan outdoor wet bulb temperature

 

OXYCELL DPC wet bulb efficiency

 

OXYCELL wet bulb efficiency

 

OXYCELL IEC cooling performance 

 

OXYCELL IEC supply temperature

 

OXYCELL IEC supply temperature

 

 

OXYVAP cooling performance

 

OXYVAP supply temperature

 

OXYVAP supply temperature

 

OXYVAP two-stage cooling performance 

 

OXYVAP+ supply temperature

 

OXYVAP+ supply temperature

 

 

 

Technology comparison 

 

Overview of OXYCELL DPC, OXYCELL IEC, OXYVAP and OXYVAP+ supply temperatures

 

Technology supply temperature comparison

 

Overview of the average indoor temperature and relative humidity within the occupied zone

 

Average indoor temperature and relative humidity

 

Summary
Summary data

*Typical value, source: McQuay International, Engineering System Solutions Edition No. 12, July 2002.

 

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