Daikin VRV III Service Manual
Introduction
The Daikin water cooled VRV® (VRV®-WIII) combines all the well known benefits of VRV® with those of water systems: The VRV® component of the system - condensing and indoor units, refrigerant piping and controls - delivers high efficiency combined with exceptional control flexibility. Heat is exhausted or absorbed via the condensing units to and from the 2-pipe water circuit as required, during cooling and heating cycles respectively.
On the water side of the system the heat source (water) is supplied to VRV® condensing units throughout the building via the water circuit, which incorporates ancillary items such as - pumps, valves, strainer, expansion tank, heat transfer equipment, air vents and water treatment equipment etc. The operating range of VRV®-WIII depends on the temperature of the water circuit, which should be maintained between 15°C and 45°C.
Application potential for VRV®-WIII:
- Tall or wide multi storey buildings not subject to limitations on length of water piping
- Applications in which the amount of refrigerant in the building is limited
- Refurbishment projects in which it is possible to link VRV®-WIII into existing water piping and use the existing heat source
- Sites where suitable alternative heat transfer sources such as district water, underground water, sea water, solar energy etc. exist
- Sites where low external noise is critical. NB! Models of heat rejection equipment (cooling towers) are available for low noise applications.
- Cold climate applications with no defrost cycle due to use of water circuit.
Basic configurations of VRV®-WIII
Basic configuration for cooling operation
In temperate climatic regions, excess heat within the water circuit can usually be exhausted via a dry cooler or cooling tower. However, alternative heat sinks can also be used, including natural water sources such as rivers, lakes and bore holes - existing process or chilled water circuits can also be utilized if fitted with heat transfer facilities.
The diagram shows that during summer operating cycles, a drop in cooling water temperature below pre set temperature level T1 causes 3-way valve bypass V1 to open. This bypass closes once more when T1 is exceeded, reducing the temperature by allowing an increased flow of water to the cooling tower. On/off control of pump and fan in closed cooling tower circuits is also provided by 3-way valve, V1.
Basic configuration for heating operation
Low pressure hot water from a boiler is generally utilized to maintain the required temperature levels within the water circuit - but steam, district/process/industrial heating systems or even solar energy can also act as the heat source.
During winter operation, water circuit temperature T2 is maintained by circulating water through the boiler (or similar) via valve V2, which shuts off immediately the pre set temperature is achieved.
Alternative solution
Cooling tower and boiler replaced by heat pump chiller. The use of a boiler and cooling tower to maintain condenser circuit temperature can be replaced by a heat pump chiller in most Southern European regions, resulting in good control options via a single package, which can be supplied by Daikin. The water circuit temperature on VRV®-WIII is outside the standard operating range of a standard heat pump chiller, hence the piping configuration is important. All engineering data books for Daikin chillers publish the operating range and specify the max and min ΔT across the evaporator (Usually 3~8°C).
To ensure maximum operating efficiency of the heat pump chiller, the following data represents the optimum selection point when using the above
configuration: -
Cooling Mode: Leaving chilled water temperature
- Highest possible leaving water temperature (16°C)
Heating Mode: Leaving hot water temperature =
- Lowest possible leaving water temperature (25°C)
Water piping elements
Water at the pre set temperature is supplied to all VRV®-WIII condensing units via a 2-pipe closed circuit.. Water temperatures within the circuit must be maintained at 15 to 45°C and pumps should be of sufficient duty to match the requirements of all VRV®-WIII condensing units. Air purging should be carried out in closed circuit systems and a strainer installed to prevent impurities from entering the water flow. Expansion tanks are also important since they allow for temperature changes within the circuit. System start up should be provided by a controller, which also regulates circuit water temperature and protects the system. Steel, stainless steel, copper and plastic but not galvanised, piping can be used.
When designing a water piping system, the following should be considered:
- Water must be supplied to the required locations according to the needs of each VRV®-WIII
- Head and friction losses should be kept at a minimum
- Water velocity should be properly controlled to avoid water streaming noise, pipe vibration or pipe expansion/contraction due to temperature differences.
- Attention should be paid to water management: impact of the water quality, corrosion prevention
- Enough arrangements should be provided for easy service and maintenance.
Heat rejection equipment
In cooling mode, the purpose of the water cooled VRV® plant is to reject unwanted heat outdoors. In an air cooled VRV®III, cooler ambient air is usually drawn across the condenser coil by means of propeller fans. High pressure refrigerant heat is transferred to the cooler ambient air and exhausted outdoors. By comparison, in a water cooled VRV®-WIII, cooling water is pumped through the plate type condenser. High pressure refrigerant heat is transferred to the cooler condenser water and exhausted outdoors.
Cooling towers types
The cooling tower is still the most common equipment used for water heat rejection. With the current drive towards energy efficiency, ground water, lakes, rivers and sea have been used as an alternative heat rejection medium. Environmental concerns and restrictions however, may limit this potential source. The cooling tower relies on the process of evaporation, enabling the condenser water circuit to be cooled to a temperature below the ambient wet bulb.
Over sizing cooling towers will lead to lower condenser water temperatures at part load operation, increasing plant efficiency.
Cooling towers are either of the "open" or "closed" type.
In an open tower, the condenser water / fluid circuit comes into direct contact with the outside air.
In a closed tower, the condenser water is circulated in the heat exchanger tubes, while an evaporating water film falls on the fins of the tube exchanger.
Open cooling towers
Open cooling towers are classified in terms of the airflow configuration. "Forced draught" and "induced draught" towers are the most common types
found in the HVAC industry. The forced draught tower is driven by a fan, which blows air through the tower. Induced draught towers pull the air through
the tower.
Depending on whether the air is drawn against the flow of the water or across the flow of water in the tower, the systems can be further classified as
"counter flow" or "cross flow" configurations.
Induced draught tower
This type of unit utilizes axial flow fans and is generally thought to be the most efficient and therefore the most popular, in use today. 
Large propeller fans on the air discharge or the top of the tower draw air counter flow or cross flow to the condenser water. Due to the higher discharge velocities they are less susceptible to short air circuits or recirculation. Noise levels are higher due to the low frequency noise associated with propeller and axial fans.
Forced Draught Tower
Forward curved centrifugal fans on the air inlet will force/push the air in either a counter flow or cross flow pattern. Centrifugal fans use more power but generate enough static pressure to overcome any problems associated with internally located cooling towers or those fitted with sound dampers. These towers are quieter than others and are particularly useful for low noise applications. The cross flow tower offers the benefit of a lower profile unit where aesthetics or plant room height may be restricted. On the other hand, the power input is approximately double that of an induced draught tower.
Readmore and Download Daikin VRV III Service Manual
| Title | : Daikin VRV III Service Manual |
| Format | |
| Pages | : 48 Pages |
| Language | : English |
| File Size | : 4 MB |
| Model | : 190059119 |
