Heat Pumps

Heat Pump TechnologyHeat Pump Technology

Worldwide demand for more energy efficient and environmentally friendly technologies have led to significant support being given to the development of the electric hot water heat pump. In Australia, this field is led by Accent Air P/L, which has specialised in the manufacture of heat pumps since 1993. Accent's expertise was recognised to the point that the company was acquired by Rheem Australia in 2007 and it now produces both Accent and Rheem branded heat pumps for water heating. Accent units have been used in a diverse range of markets and applications over the years and the Company retains its ability to work individually with clients in achieving high efficiency and innovative solutions in water heating.

The Accent Heat Pump

The Accent heat pump is internationally recognised for its energy efficiency.

In the Australian market, the Accent design sets the standard for heat pump manufacture, quality and performance. Typically, when an engineering consultant drafts the specification for a major project, they will nominate the use of "Accent" or equivalent. The unit is Australia's commercial bench-mark.

The market leading efficiency and performance of the Accent heat pump is supported by detailed laboratory testing undertaken by the University of New South Wales. Likewise, Accent product is developed with the benefit of Rheem's full refrigeration test laboratory at Rydalmere, NSW. The functionality of this laboratory allows Accent to simulate the harshest of weather conditions and to continually seek advances in efficiency and output to Australian conditions. Accent's comprehensive testing and research and development program ensures that users of its heaters can trust in their output and efficiency.

While Accent has grown to be a major manufacturer, the company prides itself on the ability to retain a direct one-on-one relationship with its clients. In this way, we are able to customise each unit to meet specific project needs

Heat pump type options

The typical heat pump design is air-to-water. In this design, the heat pump absorbs heat value from air and transfers this heat to water in the internal heat exchanger. The output and efficiency of an air-to-water heat pump is a function of its design and Accent does not compromise in its total evaporator area and air flow requirements.  While this means that the Accent unit is characteristically larger, this sees the owner benefit from a unit which provides the maximum output and efficiency for its compressor rating.  Ultimately, this results in a lower heating cost.

In this design, the heat pump uses a water as its heat source. The water may be subterranean or from an open source such as a river, lake, canal or harbour. Water provides a relatively constant heat source and this approach may provide a more constant and higher average efficiency than the typical air-to-water heat pump. The unit itself has no evaporator is and more compact and quieter than the air-to-water heat pump. Water-sourced applications are specialist projects requiring particular design expertise.

Ground-sourced or ground-coupled
The ground absorbs nearly half of the thermal energy reaching the earth from the sun. In ground-sourced design, the Accent heat pump transfer this constant temperature source to water heating via a ground loop. Like the water-sourced project, ground-sourced applications are specialist projects requiring particular design expertise.

Split systems
The Accent heat pump is typically provided as a single package unit, ready for electrical and water connections. However, the unit may be provided as a "split" unit, with a Main Unit (containing the compressor and heat exchanger) and a Remote Evaporator (containing the coil and fans). Water connections would be made to the Main Unit with refrigeration and control connections running between the two boxes.

The split unit is often used where noise or space is an issue. The Remote Evaporator may be roof-mounted, taking the air discharge point to a higher less sensitive location.

Vertical, horizontal or end discharge
The Accent heat pump is typically designed as a vertical or top discharge. This means that the fans sit on the top of the unit, with the cooled air discharged upwards.

The unit may also be manufactured as side discharge or end-discharge. The side discharge unit allows the heater to be installed under a deck or under the house. This style is also sometimes installed in the side wall of garages or plant rooms, etc where the discharge air is easily ducted externally by means of a horizontal duct.

An end discharge unit may be beneficial where space is an issue, particularly with narrow plant rooms or under-building voids.

Accent heat pumpThe picture on the right shows a side-discharge design.

Right or left-handed plumbing connection
Accent will provide either right or left handed plumbing connection of the heater to best suit the hydraulic arrangements for each project.

Component Options
Accent's standard specification is set to achieve the highest level of performance, efficiency and unit longevity. Nevertheless, virtually all aspects of unit design may be altered to suit project needs.

Heat Exchanger Material and Design
As Accent manufactures heat pumps for all types of applications, it also has a broad range of options available in heat exchanger type and material.

Accent's standard specification for pool water heating is based on the use of a titanium heat exchanger. The titanium material is impervious to chemical corrosion so this allows Accent to offer a 10 Year Warranty in relation to failure due to corrosive water chemistry.

Co-axial heat exchangers for water heating may be of conventional single-wall design or double-wall (vented), with Accent recently releasing a vented titanium heat exchanger for specialist use such as aquaculture.

The conventional heat exchanger design has a direct point of heat transfer between the pool water and the refrigerant.

The double-wall (vented) tube-in-tube heat exchanger. In this design, the application water and refrigerant circulate in separate tubes with an air gap providing a safety mechanism in case of failure of the wall of the water carrying tube. This air gap ensures that water cannot enter the refrigeration system, giving protection to the compressor and evaporator.

The air gap causes a less effective heat transfer, increasing the heat exchanger capacity needed to meet the nominal heating or chilling capacity. As such, this option has a price premium.

Specialist Treatments for Corrosive Environments
Heat pumps are often installed in highly corrosive environments, whether this is outdoor locations close to crashing surf where sea spray or salt content in air causes corrosion OR internal pool plant room installation where they may be some chemical discharge to air.

The range of options which may be considered include:

Anti-corrosion evaporator treatment
All Accent units include anti-corrosion treatment of the evaporators.  The treatments are typically a self etching epoxy water based finish that protects the refrigeration coil from corrosive agents. When cured, it is a translucent full gloss hard film with a blue tone. The process is done at the time of manufacture of the evaporator coil. Ongoing treatment of evaporators with anti-corrosion product such as Kirby Kote will be offered by Accent in service visits for plant in coastal or high pollutant locations.

Copper fins on copper coil
The evaporator may be manufactured with copper fins in lieu of aluminium. Typically, in a corrosive environment the aluminium fins will show the first signs of corrosion to the evaporator. The use of copper fins protects against this, with the coil being custom-manufactured for our use. This is a premium option.

Marine grade aluminium or stainless steel casing
The standard design of the Accent heat pump includes the use of marine grade aluminium as the casing material. This is a very robust material and is specified by many industry consultants in preference to stainless steel. However, stainless steel casing can be provided.

Electrostatic painting of the case
Painting (whether it be aluminium or stainless steel) can be provided and gives an added skin or buffer to the case.

Anti-corrosive painting of fan motors and blades
The fan motor is perhaps the most at risk component of the heat pump that is treated for corrosive environments. Painting of these components with anti-corrosive paints/oils will be done in manufacture but should also be part of the maintenance program.

Specialist coil guards
Accent units feature finned coil guards to ensure protection of the evaporator from hail, etc.

Specialist Treatments For Noise Sensitive Environments
Heat pump installation must carefully consider noise requirements, as the equipment is often required to run long duties in winter months, including over-night. The design of the Accent heat pump features a sealed electrical/compressor compartment and successfully contains compressor noise. This contrasts to many imported heat pumps that place the compressor in the air-stream, allowing compressor noise to escape with the air discharge. In addition, Accent offers various options in fan selection making the unit the quietest heat pump available.

Fan upgrade
Various options in fan selection are available, including the use of larger blade fans at lower speed, centrifugal fans, high static fans to allow ducting or acoustic fans.

Acoustic Hood
The acoustic hood provides a noise attenuation of around 2 to 3 dBA.

Compressor Jacket and Acoustic Lining
The option of a compressor jacket and added lining of the unit casing is available.

Specialist Treatments For Cold Climate Locations
The installation of air-to-water heat pumps installed in cold climate locations requires special care in unit design, capacity selection and method of deice.  Accent's access to Rheem's full refrigeration test facility has allowed it to develop specialist coil design for operation at cold ambients and this is reflected in its Cold Climate Series design. 

Hot Gas By-Pass
Deice by means of hot gas by-pass is standard in all Accent heat pumps. Under this method, hot refrigerant is bled back into the evaporative coil to maintain the coil temperature above freezing. The deice is triggered by sensing suction pressure and will occur at an air-on temperature of around 10°C.

Air Defrost Cycle
For units with hot gas by-pass deice, Accent also offers the option of an air defrost cycle. The cycle would be controlled by timers and may be changed according to seasonal needs. With this approach, the unit compressors are deactivated while the fans continue to run. The movement of air across the coil lessens or removes frost build-up.

Reverse Cycle Deice
This option provides the strongest form of deice. In this mode, the unit will switch to reverse cycle operation when the coil temperature is -5°C, thereby passing heat to the evaporator.

Twin Heat Exchanger For Automated Heating of Separate Pools
In this design, the heat pump contains twin heat exchangers and controls to allow for the automated switching of the heating function between two pools. This is typically provided for the heating of a pool and spa. The unit gives priority to the heating of the spa and will return to spa heating whenever a heating demand is sensed. As the unit's capacity will have been selected in essence for the heating of the pool, it is able to raise the spa temperature quickly.

This style of heat pump is well suited to resorts, hotels, etc where the requirement is for constant heating of the spa. The direct connection of both the pool and the spa to the unit removes the need for changing of valves in the pool/spa hydraulics.

Plunge Pool Design
The Accent plunge pool unit is a water-to-water design which provides chilling to the "plunge pool" while simultaneously rejecting the recovered heat to a "hot" pool. With this design, the priority task is the chilling of the plunge pool and the unit design includes a remote evaporator to disperse excess heat to outdoors (at times that the hot pool is at temperature).

Chilling Only
The Accent unit may be manufactured as a chiller only, providing water cooling for a variety of uses


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