Designing a System With Variable Refrigerant Flow for a Residential Apartment

Abstract

The heating, ventilation, and air-conditioning (HVAC) system is arguably the most complex system installed in a building and is responsible for a substantial component of the total building energy use. Variable refrigerant flow is varied using either and inventor controlled variable speed compressor , or multiple compressor of varying capacity in response to changes in the cooling heating required within the air conditioned space.The variable refrigerant Flow (VRF) air conditioning system as a high degree of intellectual control, with every indoor unit being able to directly start the air conditioning system, freely setting and regulating the temperature, the volume and direction of the current ,and the mode.

Every indoor unit can separately control it start and close, and regulate its operations.

HVAC design involves more than just the load estimate calculation the load calculation is the first step of the iterative HVAC design procedure. This strategy guideline discusses the information needed to design the air distribution system to deliver the proper amount of conditioned air to a space.

Heating and cooling loads are dependent upon the building location, sighting, and the construction of the house, whereas the equipment selection and the air distribution design are dependent upon the loads and each other. The Variable refrigerant flow systems may be a particularly good option for buildings with multiple zones or wide variance heating/cooling loads across many different internal zones. These systems provide individual control and the most versatile of the multi-split systems. Hotels, school and office buildings are good examples.

Introduction

Variable refrigerant flow (VRF) is an air-condition system configuration where there is one outdoor condensing unit and multiple indoor units. The term variable refrigerant flow refers to the ability of the system to control the amount of refrigerant flowing to the multiple evaporators (indoor units), enabling the use of many evaporators of differing capacities and configurations connected to a single condensing unit. The arrangement provides an individualized comfort control, and simultaneous heating and cooling in different zones.

Currently widely applied in large buildings especially in Japan and Europe, these systems are just starting to be introduced in the U.S. The VRF technology/system was developed and designed by Daikin Industries, Japan who named and protected the term variable refrigerant volume (VRV) system so other manufacturers use the term VRF 'variable refrigerant flow'. In essence both are same. With a higher efficiency and increased controllability, the VRF system can help achieve a sustainable design. Unfortunately, the design of VRF systems is more complicated and requires additional work compared to designing a conventional direct expansion (DX) system. This course provides an overview of VRF system technology.

Literature Review

Mr. Johnathan wood VRF air-conditioning systems owe their growing popularity to their ability to meet a wide range of requirements, as Tony Nielsen explains.The primary function of all air-conditioning systems is to provide thermal comfort for building occupants. There is a wide range of system types available, staring with the basic window-fitted unit through to the very latest VRF (variable refrigerant flow) equipment. Deciding which system best suits the application will depend on several variables. For example, in a modern, design-conscious office the aesthetic requirements of the client may prove of greater importance than the number of control options they provide. While a client looking for the best life-cycle cost will need to balance capital cost with long-term operatingcosts, efficiency and predicted VRF systems provide cooling and heating using refrigerant (R407C or R410A) as the working fluid. There are two basic types of VRF system cooling/heating-only and energy-recovery[1].

Tianzhenhong A VRF system's ability to control the refrigerant mass flow rate according to the cooling and/or heating load enables the use of as many as 60 indoor units with differing capacity 1989 2010 1989 2010 1989 2010 1989 2010 in conjunction with one single outdoor unit. This unlocks the possibility of having individualized comfort control, simultaneous heating and cooling in different zones, and heat recovery from one zone to another. The new VRF model in Energy Plus V8 developed by LBNL, was used for VRF system simulation in this study[2].

Hussain shah Variable refrigerant flow (VRF) system is a mature heating, ventilation and air conditioning (HVAC) technology which simultaneously heat and cool area through extracting heat from an area which needs cooling and transfer heat to another area. Variable refrigerant flow (VRF) systems are installed with air conditioner inverter that adds a dc inverter which drives the control of compressor that modulates heat or cooling in the area. The compressor unit of variable refrigerant flow (VRF) are installed on the roof of the building, and heat & cool refrigerant are connected through piping connected to condition the building[3].

RahulDhariaVRF(Variable Refrigerant Flow),sometimes known as variable refrigerant volume (VRV), is a smart climate control technology that offers high flexibility in terms of controlling temperature in different parts of a building at different times of a day. This innovative technology is becoming increasingly popular in large urban areas like Mumbai, Delhi, Kolkata, and Bangalore. VRF air conditioning system is a highly popular AC type in the market today[4].

Rajkumarsundaram Variable refrigerant flow also known as VRV(variable refrigerant volume) Means the main compressor which pumps refrigerant around can run at various speeds(stepless) thereby has an ability to continuously increase (or decrease) flow of refrigerant based on demand during various hours/minutes of usage.(Most of basic traditional units, work only by start/stop of compressor. This means either 100% flow or 0% flow of refrigerant)[5].

KarthikChandrasekaran Variable refrigerant flow, also known as VRV(variable refrigerant volume) Means the main compressor which pumps refrigerant around can run at various speeds Room thermal loads can go up or down gradually by suns heat or fluctuate rapidly when some doors are open/shut more often. Or sudden increase of rooms occupants . VRF Controls are designed to look at these fluctuations and adapt its cooling power almost like a automatic or CVT shift in a car[6].

Wilfred Alexander A challenging factor to the variable refrigerant flow (VRF) system is the guidelines that are shared by ASHRAE to control the concentration limits of refrigerant. Thus time to time maintenance is needed. The leakage of refrigerant which is being piped around the building in larger variabl refrigerant flow (VRF) system of 14-20 tons is potentially high and thus can restrain the growth of variable refrigerant flow (VRF) systems[7].

Steve reno A system capable of variable refrigerant flow should have VFD motors (variable frequency Drive) and be capable of changes to the volume of air moving through both coils.Artificially limiting outside air will raise head pressure (summer) or lower suction pressure (winter); both conditions being contrary to design[8].

G.R.K.D. SatyaPrasadet.al concluded from his paper titled “HVAC system Performance and operational strategies in Green buildings” that in most of countries, buildings represent 30-40 % primary energy use, including fuel input for production. Furthermore, today are almost exclusively dependent on energy supplied from outside, even though they have significant potential for self-support using renewable energy.

Buildings have the physical potential to harness diluted and sometimes unpredictable renewable energy. The building envelope and the ground constitute the basic resources for energy autonomous buildings. The key objective of the project is to produce new, innovative and non-conventional scientific knowledge in sustained, clean and efficient energy technologies to give a better solution for rooftop PV assisted buildings and achieving energy efficient buildings. The present work will be analyzed through simulation by using RETSCEEN software and compared with measured values and to arrive at certain general design rules for such systems[9].

Autodesk Revit Software

The REVIT software was developed by Charles River Software, founded in 1997 , renamed Revit Technology Corporation in 2000, and acquired by Autodesk in 2002. This software used for architects, landscape architects, structural engineers, mechanical, electrical, and plumbing engineers, designers and contractors. The software allows users to design a building and structure and its components in 3D, annotate the model with 2D drafting elements, and access building information from the building model's database. Revit is 4D building information modeling capable with tools to plan and track various stages in the building's lifecycle, from concept to construction and later maintenance and demolition

Methodology

• Site Selection
• Building Layout
•  Analysis
•  Placing of Vrf Units

The following system design methodology is used for HVAC design in Automobile:

Effective System Zoning: A HVAC system can be controlled via a single-zone strategy or a multi-zone strategy. With a single zone strategy, all areas served by the system receive the same amount of heating, cooling or air conditioning as defined by the control logic of the unit. However, different areas can have different energy requirements depending on a number of factors as outlined in section 2 above. Areas with similar end energy use requirements should be grouped and served from the same HVAC system. This will ensure the optimum amount of heating, cooling or ventilation is provided to the spaces when required.

Single Zone Requirements Driving a Multi-Zone System: The requirements of the areas being served by a unit should be as similar as possible, to prevent a single area driving the end energy use. For example, if an area on a multi-zone system has a humidity requirement of 40-50% RH while other areas on the system don’t require humidity control, this area should not be served by the same AHU. Smarter volume of air is being conditioned for humidity purposes than is required.

This may also result in unnecessaryheating and cooling occurring as the supply air may require cooling to remove moisture from the air and then require heating to achieve the correct supply-air temperature. This is the most energy intensive mode of operation for an AHU. It should be applied to the minimum volume of supply air as actually required, according to the real energy service requirement. All the parameters should be challenged and the reason for their specification questioned.

Waste-Heat Recovery: Waste-heat recovery devices recover thermal energy from exhaust air and transfer it to the incoming fresh-air supply. This can result in a reduction in the energy that would normally be needed to heat or cool air to the temperature requirements of the system. A correctly designed and installed heat recovery device can achieve savings upwards of 10% of the running cost of the HVAC system.

Design

SOME OF THE SHORTCUTS USED IN THE SOFTWARE

CL [STRUCTURAL COLUMN]: Adds a vertical load-bearing element to the building model.

CM [PLACE A COMPONENT]: Place a component.

DR [DOOR]: Adds a door to the room or building.

GR [ GRID]: Places column grid lines in the building design.

LL [LEVEL]: Places a level in view.

RM [ROOM]: Creates a room bounded by model element and separation lines.

RP [REFERENCE PLANE]: Creates a reference plane using drawing tools.

RT [TAG ROOM; ROOM TAG]: Tags the selected room.

SB [STRUCTURAL FLOORS]: Adds structural floors to a building model.

WA [ ARCHITECTURAL WALL]: Creates an on-bearing wall or a structural wall in the building model.

WN [WINDOW]: Places a window in a wall or skylight in a roof.

Manual steps for calculating load factors

Step 1 Finding the location, dry bulb temperature, wet bulb temperature, relative humidity, specific humidity and dew point temperature.

Step 2 Glass

Radiation: Q = µ×A×∆T

Transmission Q = U×A×∆T

Where, U= coefficient of heat transfer and µ= transparency factor

Step 3 Walls

Q = U×A×∆T

Step 4 Roof

Q =U×A×∆T

Step 5 Ceiling/Floor

Q = U×A×∆T

Step 6 Portions

Q = U×A×∆T

Step 7 Equipments

Q = w×4.16

Step 8 People = BTU/hr person × no. of people

Step 9 Infiltration

Q = CFM×1.08(Sensible)×A

Q = CFM×0.68(Latent)×A

Step 10 Ventilation

Q = CFM×1.08(Sensible)

Q = CFM×0.68(Latent)

Air Change CFM=(V×NACPH)/60 Where, NACPH = no. of air changes per hour

Step 11 Sum of sensible heat = Glass+ Wall+ Roof+ Floor/Ceiling+ Portion+ Equipment+ People+ Infiltration+ Ventilation

Step 12 Effective Sensible Heat = Total Sensible Heat×10% of Total Sensible Heat

Step 13 Sum of Latent Heat = People+Infiltration+Ventilation

Step 14 Effective Latent heat = Total latent heat×5% of Total Latent Heat

Step 15 Ton of Refrigeration = (Effective sensible heat + Effective latent heat)/12000

Step 16 Effective Sensible Heat Factor = (Effective sensible heat + Effective latent heat)/Effective sensible heat

Step 17 ADP = Apparatus Dew Point Temperature

Step 18 Sensible Heat at Heat Engine = CFM×1.08A

Latent Heat at Heat Engine = CFM×0.68

Layout of building for designing of variable refrigerant flow system

project summary

Building summary

Spaces in building

Conclusion

The variable refrigerant flow system is considered to be one of the most promising energy saving technologies gaining its momentum in recent year. A variable energy efficient technology is needed to conserve energy as well as to achieve better human comfort.

So this is been new and efficient way to design HVAC system with VRF technology. It provides realistic choice to traditional central systems. Its brings some of the latest technology to the market and provides a higher degree of reliability, comfort and energy efficiency that is expected from today’s consumer

References

1. Mr. Johnathan wood VRF air-conditioning systems Dynamic Simulation of Energy Management Control Functions for HVAC Systems in Buildings, Energy Conversion and Management 47 (7–8), 926-943.
2. Tianzhenhong International Energy Agency (IEA), World Energy Outlook, OECD/IEA, France, 2012. www.worldenergyoutlook.org/publications/weo2012.
3. Hussain shah Heating and Cooling Energy Trends and Drivers in Buildings, Renewable and Sustainable Energy Reviews 41, 85-98.
4. RahulDharia Variable Refrigerant Flow Systems, ASHRAE Journal 49 (4), 24-31.
5. Rajkumarsundaram Experimental Evaluation of the Ventilation Effect on the Performance of a VRV System in Cooling Mode-Part I: Experimental evaluation, HVAC&R Research, Vol.14, No.4, 615-630.
6. KarthikChandrasekaran Simulation Evaluation of the Ventilation Effect on the Performance of a VRV System in Cooling Mode—Part II: Simulation Evaluation. HVAC&R Research, Vol. 14, No. 5, 783-795.