– Adaptive Defrost Technology
Adaptive Defrost Technology
From field experience to engineering innovation, we’ve invented a smart way to effectively defrost airHome heat pumps during extreme cold climate and high humidity conditions.
General defrosting principles: all heat pumps must defrost!
It is not always known by heat pump owners that their system automatically defrosts the outdoor unit during heating operation in winter.
Why is that? During the heating season, as the heat pump is heating the room, the condensing unit extracts heat from the ambient air. Once the heat is extracted, naturally present humidity condenses on the heat exchanger and the very cold temperature of the air exhaust causes the condenser coil to feeeze over time.
To remove the frost that forms, every heat pump performs a regular defrosting cycle which temporarily stops the heating operation. During this defrosting cycle, instead of circulating the hot refrigerant fluid inside the room, it will pass directly to the outdoor unit’s coil to remove the frost.
This defrosting operation is designed to be quick and unnoticed by the room occupants, as the room’s temperature remains stable. As per factory settings, defrosting cycle is minimized by consistently monitor heat exchanger, ambient and load conditions. Ultimately, this will help maximize heating cycle for end users and minimize defrost run times and cycles.
Our observations: Insufficient defrosting in very cold & humid weather
Hitachi Cooling & Heating partners in Quebec, Canada, observed that, when the outdoor temperature drops to extreme cold and the ambient humidity is high, especially in locations near rivers, the standard defrosting cycle would not completely remove the frost from the condenser. Over time, ice kept forming at the lower part of the condenser and the drain hose would freeze, despite the regular defrosting cycles.
Our engineers at simulated similar defrosting conditions in their labs, verifying the field observation. The extensive tests confirmed that in harsh cold climate conditions, some frost would keep accumulating on the coil over time.
“Insufficient defrosting in these unique cold climate conditions damaged the heat exchanger and ice blocked the drainage of condensate” explains Samuel Vivar, Direct Expansion Product Portfolio Manager for North America.
“We wanted to solve this issue to assure that Hitachi airHome heat pumps were a reliable heating solution for the colder regions in North America”.
Hitachi innovation: unique technology adjusting the defrost cycle to icy conditions
To make sure that the defrosting cycle would eliminate 100% of the frost, our expert engineers have developed an advanced algorithm, enabling the outdoor unit’s to detect insufficient defrosting and boost the next defrost to reach 100% effectiveness.
The new Adaptive Defrost Technology works in two major steps:
1. Detection of insufficient defrost
A good indicator of defrosting’s effectiveness is the refrigerant temperature at the end of defrosting, known as ‘defrost release temperature’. The engineers defined that the defrost release temperature should remain above 64° F (18° C) for an effective defrosting.
If the airHome heat pump detects a temperature below 64° F (18° C), it can accurately predict that some frost remains on the coil. Thanks to this constant monitoring, the airHome heat pump can activate a special defrosting for cold climates every time it’s necessary.
By adding an innovative defrost temperature sensor at the outdoor unit’s pipe, the airHome units became smarter and could now predict when the regular defrosting process was inadequate.
2. Adaptive defrost cycle to remove 100% of frost and ice
By developing multiple scenarios for various cold temperature and heat load levels, the new Adaptive Defrost Technology’s smart algorithm makes sure to adopt the suited and specific defrost cycle to completely remove the frost.
- Addition of a heater at the base of the drain pan, which activates after 30 seconds when the ambient temperature drops below 0° C / 32°F . This extra boost of heat ensures that all ice and frost are melted away.
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Advanced algorithm adjusting cycle duration. If the defrost temperature sensor indicated that the refrigerant is below threshold, the algorithm shortens the interval between the next defrosting cycle down to 30 minutes, to prevent accumulating too much frost on the coil. In any case, for all defrost cycles (standard or special for cold climates) the Adaptive Defrost Technology shortens the duration of defrost cycles, resulting in accrued end user’s comfort in heating season.
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Advanced algorithm for adaptive cycles: If the defrost temperature sensor indicated that the refrigerant is below threshold, the algorithm shortens the interval between the next defrosting cycle down to 30 minutes, to prevent accumulating too much frost on the coil.
Proven effectiveness
A series of tests were conducted in Johnson Control-Hitachi’s certified labs to confirm the effectiveness of the new Adaptive Defrost Technology.
“We pushed our environmental chambers to the most extreme conditions: 100% humidity at -13° F (-25° C) and sprayed water on the coil to create more frost. We wanted to make sure that the defrosting could withstand the harshest conditions in cold climate regions” says Sandeep Verma, lead engineer of the Adaptive Defrost Technology.
Figure: Adaptive Defrost Technology test
Conditions: Heating indoor unit at 69° F (21° C), outdoor air at 17° F (-8° C) with 87% humidity
Figure: Adaptive Defrost Technology test, extreme conditions 100% humidity at -13° F
Questions & Answers
Do all Hitachi heat pumps have the Adaptive Defrost Technology?
The airHome 600 and 800 series, equipped with HeatForce technology, include the Adaptive Defrost Technology. The airHome 400 has adaptive defrost but not as enhanced as the HeatForce models since it’s not intended for cold climate applications. The airHome Multi will not have the adaptive defrost technology but will have an enhanced defrost due to software improvements.
Is there any way to manually enable/disable Adaptive Defrost Technology?
By default, the heat pumps embedded with Adaptive Defrost Technology will automatically activate special defrosting when the standard defrost cycle becomes insufficient in cold climate conditions. There’s no disabling option as it helps sustain the performance of the heat pump.
What is the difference between Adaptive Defrost Technology and FrostWash outdoor units?
The purpose and processes of these two features are completely different. FrostWash in outdoor units is a self-cleaning functionality, which freezes and melts the coil to remove dirt from the condenser. It’s useful for any season, whether the heat pump is in cooling or heating mode. The Adaptive Defrost Technology delivers enhanced defrosting cycles for heating operations in cold climates.
Does Adaptive Defrost Technology reduce energy efficiency, due to the base pan heater?
Considering that insufficient defrosting affects heat exchange and reduces energy efficiency of your system, the Adaptive Defrost Technology preserves the energy efficiency of your heat pump instead of damaging it by enhancing the heating capability.
Also the base pan heater activates based on ambient condition only when it’s needed, as the advanced algorithm turns it off when defrosting can be effective without using the base pan heater.
