A quantum leap in energy efficiencyThe HVAC market is rapidly changing. Inverter technology is the most energy efficient technology and is currently revolutionizing the way air conditioning systems are being designed and built to meet climate control needs around the world. The first to embrace variable-speed technology gains a competitive advantage.
Market needs: Avoid system oversizing, reduce electricity bill and inrush current, increased comfort and process are some key drivers for variable capacity.
Modulating technologies: There are several ways to modulate the cooling capacity in refrigeration or air conditioning and heating systems.
Bypass method
Working principle: Inverter compressors operate at different speeds generating a modulated refrigerant mass oil flow and cooling output.
Benefits: Better power supply quality, system diagnostics, humidity control, energy savings, accurate temperature control, less noise, process safety, greater comfort
Challenges: Compressor and drive selection, designer skills makes the system overall reliability and efficiency.
By using the Danfoss inverter compressor solutions, significant energy savings can be achieved compared to traditional on-off compressors or mechanically-modulated technologies.
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Better power supply quality, system diagnostics, humidity control, energy savings, accurate temperature control, less noise, process safety, greater comfort.
Inverter compressor technology offers new opportunities for air conditioning systems, first of all in terms of energy efficient buildings, reduced energy consumption and lower running costs.
Additionally, the technology improves power factor leading to better power supply quality as well as better system diagnostics and open communication protocols which facilitate servicing.
Continuous adaptation to cooling demand provides higher energy savings and accurate temperature control.
The compressor matches power input with cooling capacity. The unit copes effectively with changes in temperature and runs at partial load which can represent over 30% reduction in the energy bill every year compared to a fixed speed or mechanically modulated compressor. The stable temperature control secures the processes in an optimum way and provides greater comfort. All in all, this means energy efficiency in buildings.
The capacity modulation attenuates power demand peaks which also contribute to increasing the grid reliability and quality of power supplied.
The soft start control leads to a near zero inrush current and improves EER:
Additional benefits are of inverter compressors are:
This adds to the long list of benefits to manufacturers, consulting engineers and end-users in terms of:
Figure 1
Energy consumption for cooling systems using different compressor configurations. Average consumption index based on simulations for 10-30TR compressors used in applications with low pressure ratio (rooftop); Index 100 = Danfoss inverter scroll VZH energy consumption.
Figure 2
Typical load profile in a building.Only a few percentages of operations are at full load in a building. HVAC systems are designed for peak conditions (right side of the graph). These conditions are not those conditions in which the equipment will operate most of the time. This graph represents typical annual climate data and hours of run time (% of year) for each condition.
Source: Danfoss HVAC tool
Compressor and drive selection, designer skills makes the system overall reliability and efficiency.
Importance of the inverter drive: The compressor and drive need to be qualified to work together and for dedicated applications. The drive modulates the compressor speed and prevents it from operating out of the compressor operating limits. The inverter frequency drives need to use algorithms developed specifically for heating, ventilation and air conditioning (HVAC) or for refrigeration. They ensure that the system will run within the application constraints. The drive can also manage other devices such as oil injection valves or multiple compressors. As the compressor rotational speed changes, the amount of refrigerant — and oil — flowing through the compressor increases or decreases. The drive ensures that the compressor is optimally lubricated at all compressor speeds.
OEM manufacturer skills in inverter system integration: not all OEMs are yet prepared to adopt inverter technology due to following reasons:
Misconceptions about variable speed technology
Inverter technology reacts too slowly to load changes: some inverter scrolls ramp up/down speed range is between <0.1s; 3600s>Full load inverter losses 5-10% at full speed the inverter car lose 3% of efficiency. As full load is not the dominant profile, the loss will be minimal in the overall unit consumption.
Oil circulation increases at high frequency operation: oil circulation rate electronically controlled by some inverter scrolls can be less than 3% at full speed. Oil management is more complex with inverter compressor systems. Some inverter scrolls control oil circulation at both low and high speed requiring minimal design accommodations.
Inverters can't be used where EMC (Electro Magnetic Compatibility) is a concern: some inverter solutions offer 2 levels of EMC filtration which meet the most stringent European standards related to electromagnetic interference.
Avoid systems oversizing, reduce electricity bill and inrush current, increased comfort and process are some key drivers for variable capacity.
Many refrigeration and air conditioning systems require reliable processes which are more efficient, compact, environmental friendly, easy to install and to maintain. The cooling requirements vary over a wide range during the day and over the year due to ambient conditions, occupancy and use, lighting etc.
Three different market trends are converging to create new opportunities for efficient, sustainable solutions:
Energy efficiency is no longer an option. Energy regulations are strengthening. Building energy codes and standards are developed globally and energy incentives are getting more attention. Another global issue is the energy security. How to make sure that we will not lack of energy one day?
HVAC and refrigeration systems are usually designed for peak demand which represent only a small percentage of the actual operation. Such oversizing leads to efficiency losses and extra costs for oversized equipment. Energy efficient capacity modulation is a way to match cooling capacity to cooling demand thereby matching these application requirements.
There are several ways to modulate the cooling capacity in refrigeration or air conditioning and heating systems. The most famous common in air conditioning are: on-off cycling, hot gas bypass, manifold configurations of multiple compressors, mechanical modulation (also called digital) and inverter technology. Each has advantages and drawbacks.
Air-conditioning is responsible for approximately 20% of the total annual electricity consumption in a country like the USA. The introduction of inverter drive technology in air-conditioning and heat pump systems presents an opportunity for significant energy savings due to efficient part-load operation, and also helps improve power quality of the grid.
Power factor is an important measure of how hard the power utility must work to deliver electricity.
Increasing the power factor of installations can directly impact the quality of power supply. For electric utilities, this equates to fewer losses and improved reliability of service. For building- and homeowners, this means more efficient equipment with the possibility of local utility, state and/or federal incentive programs.
Power factor is the combination of the displacement power factor (displacement of active and reactive power) and the distortion power factor (distortion of the electrical power due to harmonics).
Power factor close to 1 means:
The use of inverter drives allows a significant enhancement in power factor, since the displacement power factor is close to 1. The distortion power factor however negatively affects transformers, cabling, fuses and circuit breakers due to harmonics.
The Danfoss inverter technology has a low distortion and high power factor (0.98) due to correction from a DC choke whilst other inverter frequency drives or mechanically modulated systems can have a power factor as low as 0.60.
Other benefits of the prequalified drive correction in Danfoss inverter solutions:
An inverter compressor is designed to operate with a drive which steplessly adjusts the speed of the compressor motor to deliver the cooling need.
It can either be a scroll, rotary or reciprocating, semi-hermetic, open compressors, including screw, centrifugal and axial compressors. This type of compressor uses a special drive to control the compressor motor speed (measured in round per second RPS). Inverter compressors can operate at different speeds: the inverter compressor is specifically designed to run at different motor speeds thereby generating a modulated refrigerant mass oil flow and cooling output.
The variable frequency drive indicates the cooling requirement to the compressor motor. The motor continuously adapts speed to produce more or less cooling capacity to match the exact cooling need. The combination of the two devices – compressor and drive – gives a continuous cooling modulation. The variable speed principle requires a very sturdy compressor for full speed running and a special compressor lubrication system for systems using oil. Excellent oil management is a critical requirement to secure compressor lifetime. The oil management system guarantees good lubrication of the scroll set at low speed and prevents excess oil from being injected into the circuit when operating at full speed to maintain a perfect Oil Circulation Ratio.
Danfoss reciprocating inverter compressors avoid oversized and short cycling systems. The compressor automatically adapts to the current load. By combining an efficient Danfoss Maneurop® reciprocating compressor with a Danfoss Drive, we provide an innovative and intelligent package that utilizes variable-speed technology to ensure superior efficiency across the entire operating range for precision cooling.
Danfoss inverter scroll compressors for commercial air conditioning use variable-speed technology to deliver the highest possible cooling capacity and energy efficiency.
Danfoss Turbocor® model TTS oil-free compressors are available in four different models ranging from 60 tons to 200 tons / 200 to 700 kW utilizing R134a or low GWP R513A.
Danfoss Turbocor® model VTT oil free compressor is available with a capacity up to 400 tons / 1430 kW using R134a. This compressor is designed for water and evaporative cooled chiller applications.
Danfoss Turbocor® model TGS oil free compressors are available in 5 different models ranging from tons to 150 / 140 kW to 540kW utilizing ultra-low GWP R1234ze or R515B.
At Danfoss we have all the refrigeration solutions, experience and know-how to act as a competent and trustworthy partner for the global air drying industry.
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VFDs are used for a wide range of motors, not just RTU fan motors. Danfoss was able to pre-program the VLT® Micro Drive specifically for RTU applications and offer it to contractors. Because the programming work is done upfront, the contractor simply mounts the drive inside the RTU, wires it up, and enters the nameplate installation. Most mechanical contractors can do the job in about half a day.
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Coolselector®2 is essential software for engineers, consultants, and system designers who work in the refrigeration and air conditioning industry. Using Coolselector®2, you can easily optimize energy consumption and increase efficiency in your HVACR system — simply run calculations based on your operating conditions and then choose the best component setup for your design.
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