VRV , multisplit or something else 2

[pipedesign]

I would like to know the diference between VRV systems and multispilt systems. Is one better then the other, or there is a better system then those two ?
Thank you very much !

 

[arabei]

Hi pipe design, below is an article that i've found once i surfing the web in one of those precious moments that you can get sometime for yourself.

Practical Guide to Multi-split Systems and Variable Refrigerant Volume (VRV) Systems
by Mike Hardy

Introduction
There are many manufacturers of multi-split systems and VRV systems throughout the world and it is important that the designer / specifier / building owner has some practical understanding of their uses and limitations. These type of systems vary considerably from manufacturer to manufacturer particularly with reference to noise levels and the type of indoor units used. This is particularly the case with VRV systems where it is often assumed, quite erroneously, that there are few manufacturers of these systems and they are all similar - this is not the case.
The above systems have come of age in the last 5-10 years and are particularly popular because they require less outdoor plant space than conventional systems, are less disruptive to fit in existing buildings (particularly when occupied), are able to cool and heat through common pipe work and in the case of VRV systems have inherent heat recovery.
These systems all use refrigerant as the cooling / heating medium rather than chilled water / hot water as is used in conventional hydraulic systems circulated by pumps.
Condensing units are used externally when cooling only is required and heat pumps are used externally when both cooling and heating are required.
Multi-split Systems
The traditional 'split system' is also known colloquially and more descriptively as a 'one to one split system', meaning one external condensing unit / heat pump is connected by refrigerant pipe work to one indoor cooling / cooling and heating unit.
The multi-split system uses one external unit which is connected to several indoor units. The multi-split system takes a number of different forms and it is essential the designer / specifier understands the limitations of each type of system.
Master and slave system
One off external condensing unit / heat pump unit is connected to several indoor units as is typical for a multi-split system. One of the indoor units is provided with temperature controller / sensor and acts as master and the other unit(s) acts as slaves. All indoor units will therefore function as the master setting. Master and slave units are suitable for single areas, single rooms or even multiple rooms with very similar heat gains / losses. They are not suitable for individual areas / rooms which have different heat gain / loss characteristics because the master control will sense air temperature for one area / room only and the areas / rooms will overcool or overheat.
Zoned control units
As previously one off external / heat pump unit is connected to several indoor unit. With these systems each indoor unit has its own individual temperature controller and thus each unit functions as required to maintain the individual room temperature. With these systems whilst there is individual control the limitation is that if cooling is required in one area it is not possible to provide heating in a different area served by the same system because the compressors will function in only cooling mode or heating mode.
Variable refrigerant volume (VRV) systems
Again one off condensing unit/heat pump is connected to several indoor units. VRV systems are able to provide total versatility and each indoor unit may cool / heat independently of each other. In fact, if part of a building requires cooling and other areas require heating the heat rejected for the required cooling contributes or is recovered to provide heating in the other area.
Refrigerant Pipe work Limitations
The maximum lengths of pipe work it is possible to use for all mass produced refrigeration equipment is determined by the compressor. All 'split' systems therefore have a maximum vertical and total refrigeration pipe work length allowable. This is a considerable disadvantage compared with hydraulic systems which are pumped and as the pump may be sized to suit the system, then theoretically, the hydraulic pipe work may be run almost infinite distances. It is important the designer / building owner is aware of these limitations. Each manufacturer specifies both the size of the pipe work required for their system and the maximum permissible vertical and total refrigerant pipe work runs.
Moreover it may not be assumed that these distances will be similar between manufacturers for similar capacity equipment this is often not the case. However a nominal guideline is as follows:
Up to 5 kW of cooling maximum of 25 meters
Up to 7 kW of cooling maximum of 25 meters to 50 meters (varies widely between manufacturers)
Up to 15 kW of cooling maximum of 30 meters to 50 meters
VRV systems and zoned systems generally up to 50 meters vertically and 100mm overall. Typically one outdoor unit may be connected to up to a maximum of 8 indoor units.
(Some manufacturers produces a zoned system which allows up to 16 indoor units to be connected to one outdoor unit.)
Indoor Units
All indoor units used with multi-split systems provide air distribution by mixed flow and come in various forms:
Floor standing units
Units mounted on walls at high level
Unit mounted below a ceiling
Cassette units which recess within a false ceiling and terminate with a grille flush with the false ceiling through which air is supplied and exhausted to the space.
Ducted units or 'void pack' units mounted above a false ceiling and are generally connected to ductwork terminating in the ceiling with supply and exhaust grilles to the space. These ducted units may take the form of 'low static' pressure units or 'high static' pressure units.
With reference to (e), the size and type of the fan motors in these units vary considerably from manufacturer to manufacturer and this determines the extent of the ductwork allowable which is a function of the static pressure of the fan. Silencers may also be provided within the ductwork for very low noise levels required in such spaces as recording studios, but again the fan static pressure available has to be checked carefully so the pressure drop through the silencers may be overcome by the fan.
Outside Air
The introduction of outside air to all 'split' systems is often a problem (typically 8 L/S per person is required). To overcome this some manufacturers provide a heat recovery unit which provides outside air to the air conditioned space independently of the indoor units. With these systems an equal quantity of outside air and exhaust air is supplied and then exhausted from the air conditioned space. The supply and exhaust air passes over a heat exchanger so heat is recovered from the exhaust air and used to heat or cool the outside air. This solution has the limitation that air is introduced to the space at two different temperatures, i.e. that of the indoor unit and that of the heat recovery unit. If possible it is always ideal to introduce outside air to the indoor unit. It is possible to introduce outside air to the following indoor units:
Cassette units
Some manufacturers provide cut outs on the side of the unit so outside air may be ducted into the side of the unit above the false ceiling. The length of the outside duct has to be carefully considered and if over a certain length may have to be fan assisted. Most manufacturers publish maximum permissible lengths and / or pressure drops. As the outside air will bypass the cassette filter the ductwork should also be provided with a filter.
Ducted unit
Provision may always be made for introducing outside air into the return air ductwork.
Applications
The application of multi-split, zoned and VRV systems should be carefully considered. Whilst the VRV systems are the most versatile the capital outlay for the equipment is far higher than for the other systems.
Multi-split and zoned systems
With most of these systems generally it is possible to provide individual control to each indoor unit (the exception being the master and slave system previously described). The sensor will provide cooling or heating as and when required to maintain the set point temperature selected.
The systems are therefore applicable when there is a clearly defined heating and cooling season i.e. cooling only required throughout the building or heating only required throughout the building. With the increased prevalence of heat producing I.T. equipment within buildings this needs some consideration because if one particular part of a building requires cooling 12 months of the year this system would not be appropriate. The solution in this case would be either to use a V.R.V heat recovery system or have an independent system dedicated to that part of the building.
With the larger zoned systems typically it would be possible to connect up to 16 indoor units to one external unit. With most manufacturers the units may be mixed i.e. an assortment of ducted, cassette, wall, floor, and ceiling units connected to the one outdoor unit.
VRV systems
These systems are the most versatile of the multi-split systems as the indoor units may function individually and will heat or cool individually. These systems are widely used in commercial offices.
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About The Author,
M.J. Hardy, C.Eng, M.C.I.B.S.E., M.I.W.Soc.
Mike Hardy is the Managing Director and founder of Ambthair Services and has been designing and overseeing building service systems for over 30 years. He was originally trained at G.N.Haden Ltd. (now Haden-Young Ltd.) as a student apprentice, and after training and successfully passing the qualifying exams required for membership of the Institute of Building Service Engineers spent several years in Africa designing and overseeing, in particular, air conditioning systems.
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N.B.
Control system used in Multi-Split Systems (Reference, Carrier 38HDC Multi-Split Duct-Free Cooling Systems)
38HDS outdoor condensing unit:
The outdoor unit is equipped with a control that monitors the indoor fan coil cooling request. The control turns on solenoid valves for the appropriate indoor fan coil unit system. The control also combines the cooling requests to control up to 2 compressors.

The 38HDS control provides a 2-minute compressor time-delay circuit which disables the compressor for 2 minutes at unit start-up. The time delay device timers are initialized when the unit is powered up (for the first 2 minutes).

The 38HDS unit control includes an integral head pressure control function. This function maintains a minimum head pressure by cycling the outdoor-fan motor in response to inputs from the thermistor (for outdoor ambient temperature) and the transducers (for system discharge pressures in each compressor circuit). The head pressure for the compressor(s) is monitored to control the outdoor fan output. The control reads an outdoor temperature thermistor to determine if the head pressure should be used to control the fan output.

Operation

The 38HDS unit receives a 24-v control signal from each fan coil unit as each fan coil unit initiates a demand for cooling. The 24-v signal energizes a control relay in the 38HDS unit (one relay per fan coil unit).
The refrigerant flow to each fan coil unit is controlled through a solenoid valve (one valve per fan coil unit). The solenoid valve(s) will not open until compressor operation is initiated by the controller. The microprocessor control in the 38HDS unit includes a 2-minute, anti-short cycle, time-delay function. This function provides a minimum off delay between compressor run stages (2 minutes each from the end of the last on period to the beginning of the next on period). If more than 2 minutes have passed since the end of the last on period, the compressor is ready to restart with initiation of demand from any fan coil unit on its circuit.

Increased Demand for Cooling

NOTE:

There are 2 separate compressor circuits in the 38HDS048 units (circuit A and circuit B). Each circuit operates independently, and will operate as follows (as will the single-circuit 024 units) upon receiving the first 24-v cooling demand signal from a fan coil unit:
1. After the 2-minute time-delay function is satisfied, the appropriate compressor starts.
2. The solenoid valve connected to the fan coil sending the demand signal is energized (at the 38HDS units).
3. The outdoor fan starts, and its operation is controlled by the microprocessor. When a second fan coil unit
signals a demand for cooling, its associated solenoid valve is energized immediately, allowing refrigerant to
flow to both fan coil units simultaneously.

Decreased Demand for Cooling

When a fan coil unit’s demand for cooling ends, the 24-v signal to the 38HDS unit stops, and the appropriate solenoid valve closes. If the other fan coil unit on this circuit still has a demand, the appropriate compressor continues to run as long as necessary for the second fan coil unit. When the second fan coil unit’s demand for cooling ends, its solenoid valve closes, and the appropriate compressor stops. The compressor will not start for at least 2 minutes after the end of this cycle due to the time-delay function. On size 024 units, when the compressor stops, the out-door fan also stops. On size 048 units, outdoor fan operation may continue under control of the 38HDS microprocessor if the other refrigerant circuit is still operating. The outdoor fan only stops when both compressors are off.

Note:
On 38HDS048 units with 2 compressors running, the compressor with the lower head pressure controls
the fan operation. If only one compressor is running, that compressor controls the fan operation.

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[Tayfun]

if you dont need very long pipes and if your building is not a very big one, probably multi split will be chipper. There are no other difference. Both are frequency controlled and aproximately have the same efficiens. On the other way if your building is a big one we should study on more proffesional, and we have to know conditions of your country. I mean fuel prices.