This principle drawing introduces a space air conditioning system with some main HVAC (Heating Ventilation and Air Conditioning) applications where variable speed AC drives can be used. This simplified diagram is for space cooling but the cooling can be replaced by space heating instead. The variable speed AC drives are not always used in all these applications but in the modern buildings at least some of these applications are usually controlled by AC drives.
The purpose of the air conditioning system is to maintain the air quality for working and living in the room or space. These “Comfort Zone” requirements are:
- Temperature 22-26 °C
- Relative humidity 30-70%
- Air change 35 m3/hour/person
- Air speed 0.15 – 0.25 m/s
- CO2 content less than 0.1%
This system for space cooling of the room (9.) has both exhausts fan (1.) and supply fan (2.). The air volume is controlled with AC drives (8.) according to the temperature and pressure requirements to keep the comfort in the room. The supply air is flowing through a heat exchanger (10.), which is cooled with water circulated by the chilled water pump (3.). The chilled water flow is controlled by an AC drive. The chilled water is cooled in the head exchanger (7.) and the primary side of the heat exchanger is the evaporator of the chiller compressor (4.). Chiller compressor capacity is controlled by an AC drives and the water circulated by the cooling tower pump (5.) cools its condenser. The pump flow is controlled by an ABB AC drive. Cooling tower fan (6.) makes the cooling water cooling and the fan capacity is controlled by an ABB AC drive.
Performance in Creating Comfort Zone
The use of variable speed AC drives improves the controllability of the whole heating, cooling and air conditioning system, enabling good possibilities to maintain the Comfort Zone. THe use of variable speed drives usually increases the first-cost of investment but through savings in electrical energy in motors along the investment in VSD has pay-back time between 0.2 – 3 years. In addition to savings in electrical energy, there are several important customer benefits speaking for VSD:
- Fast control to maintain the comfort zone conditions
- Accurate control to keep the desired air quality
- Reduced consumption of heating and cooling energy
- Reduced consumption of electrical energy
- Simple to keep the noise level down