Contact Azane
Terms & Conditions
Star Refrigeration
  • Home
  • Products
  • Sectors
  • Case Studies
  • News
  • Why Low Charge Ammonia?
  • Videos
  • About Us
  • Careers

ASHRAE - Still Water

Published by ASHRAE | Written by Dr. Andy Pearson 

We are still thinking about the role of water in refrigeration, so we turn to the old-style absorption refrigerators. I was asked the question recently “why is the hydrogen pressure in a refrigerator so high?” If you are thinking “what hydrogen?”, then what follows may come as a surprise.

Refrigerators now are almost all built with compressors using R-134a (about two-thirds of the market) or R-600a, aka isobutane, which is almost universal in Europe and accounts for about one-third of the global market. However, from the earliest domestic refrigerators, developed around the turn of the 20th century, until the mid 1970s, the absorption cycle was commonly used. These machines usually had a small electric heater to drive the system but could be powered by gas, which makes them popular in small refrigerators for mobile homes and RVs.

The absorption cycle was originally developed in the 1850s in France—before the idea of using a compressor to drive refrigerant around the system caught on—and it initially
used a mixture of water and ammonia. In these systems the ammonia is the refrigerant and the water is there to provide the impetus for the ammonia to migrate from one part of the system to another. The early French systems worked in a batch process, gradually transferring the strong ammonia solution from one part of the system (like the high-pressure receiver in a vapor compression system) via the evaporator to the low-pressure side. 

They would then need to be re-primed, like rewinding an old clock, before being set to work again. In large systems the addition of a solution pump to raise the strong ammonia solution to high pressure enabled the process to be automated, but this was not desirable for the domestic units, especially the gas-fired ones. This is where the hydrogen comes in.

The addition of a third fluid is sometimes credited to Albert Einstein and his colleague Leo Szilard but respect probably should go first to the Swedish inventors Baltzar von Platen and Carl Munters, of desiccant wheel fame. By creating a three fluid system, they managed to get rid of the need for manual intervention without using a mechanical pump. A liquid trap at the condenser outlet (like the drain from a basin or a toilet) keeps the hydrogen gas in the evaporator. As ammonia gas condenses and flows through the trap, it encounters this zone of the system where the hydrogen creates a low partial pressure for the ammonia. The total pressure in the system remains the same, but if the ammonia only accounts for a small proportion of it then it will boil at low temperature, creating the cooling effect. The boiled ammonia is sucked back into the pool of water where it is heated to separate it from the water and sent back up to the condenser. The whole system runs at about 200 psig (1400 kPa), which means the ammonia condenses at about 100°F (38°C). When the liquid drains to the evaporator it boils under a partial pressure of 10% of the condenser pressure, at about 6.5 psig (45 kPa), which is –15°F (–26°C).

If this seems improbable check the January 2013 column, which featured the insights of the self-taught English natural philosopher, Mr. John Dalton. So the answer about high operating pressure is, in effect, “because it wouldn’t get cold enough otherwise.” The pressure needs to be high enough for pure ammonia to condense at whatever temperature
the kitchen is; so there needs to be enough hydrogen in the low-temperature part of the circuit to ensure the ammonia gets cold enough to be useful when it gets there.

One quirk of these systems is that, on rare occasions and particularly after long periods switched off, the liquid trap at the condenser outlet would dry out, allowing the hydrogen
to flow up from the evaporator and stop the condenser from working. The solution to this dryout was to turn the refrigerator upside down for a moment, enabling the pool of liquid in the bottom of the unit to flow back into the trap. It was watching my father do this to an ancient fridge when I was about seven years old, and we had just arrived at a holiday cottage, that first captured my interest in all things fridgy. This really was a dark art. Of course, you had to remember to take the eggs and milk out first otherwise it would be pancakes for breakfast, lunch and supper.

Andy Pearson, Ph.D., C.Eng., is Group Managing Director of the Star Refrigeration Group and President of group subsidiary Azane Inc, the leading US manufacturer of low charge ammonia chillers and freezers.  

This article was published in ASHRAE Journal, July 2016. Copyright 2016 ASHRAE. Reprinted here by permission from ASHRAE at www.azane-inc.com. This article may not be copied nor distributed in either paper or digital form by other parties without ASHRAE's permission. For more information about ASHRAE, visit www.ashrae.org.

Latest News
  • 20.11.2018
    Azane set new benchmark in low charge ammonia refrigeration technology at RETA National Conference 2018

    Leading US manufacturer of low charge ammonia refrigeration systems, Azane, have launched their new and imp...

  • 14.06.2018
    Azane Inc to promote widespread benefits of low charge ammonia at Gustav Lorentzen Conference on Natural Refrigerants

    Caleb Nelson, Vice- President of US low charge ammonia refrigeration manufacturer, Azane Inc, will present ...

  • 20.03.2018
    Azane Travels to IIAR 2018 Annual Natural Refrigeration Conference in Colorado

    Low charge ammonia chiller and freezer manufacturer, Azane Inc, is gearing up to exhibit at the IIAR 2018 N...

  • 26.09.2017
    Low charge ammonia manufacturer Azane to deliver technical ammonia paper at RETA National Conference 2017

    RETA’s conference  brings thousands of industry experts and manufacturers under one roof. Azane Inc will be...

  • 08.06.2017
    Azane Inc to showcase innovative low charge ammonia refrigeration systems at Global Cold Chain Expo in Chicago

    US low charge ammonia manufacturer, Azane Inc, will be sharing its innovations and years of experience in a...

  • 08.06.2017
    Azane-Inc to sponsor major industry event in California

    Azane Inc, a world-leading manufacturer of low charge ammonia refrigeration systems, is thrilled to announ...

Details

Azane-Inc
913 SW Higgins Ave
STE 105
Missoula MT. 59803

info@azane-inc.com
Tel: +1 888-882-9947

Products

Azanechiller 2.0
Azanefreezer

Sectors

Frozen Storage
Chilled Storage
Process Cooling
Leisure
HVAC Cooling

Star Refrigeration Group

Star Refrigeration
Star Technical Solutions
Starfrost
Star Learning Solutions
Star Renewable Energy
Star M & E Solutions
Azane

Follow @lowchargeNH3

©2007 - 2016 Star Refrigeration. All rights reserved.   Privacy Policy   Terms and Conditions