W. Travis Horton

Application of a hybrid control of expansion valves to a domestic heat pump and a walk-in cooler refrigeration system

Hybrid refrigerant flow control, as proposed by Kim et al. (2008), employs a primary expansion valve that provides most of the pressure drop between the condensing and evaporation pressures, while small secondary balancing valves in the distributor lines to the circuits of the evaporator adjust the refrigerant flow to provide equal circuit exit superheats. In this article, experimental results for the application of the hybrid control of expansion valves to a 3-ton (10.6-kW) R404A walk-in cooler refrigeration system and a 5-ton (17.6-kW) domestic heat pump are presented. For the walk-in cooler refrigeration, initial data was taken using the inbuilt thermostatic expansion valve. Baseline data with an electronic expansion valve was taken for both systems to determine the best possible performance without using individual circuit flow control. After that, secondary balancing valves were inserted into the distributor lines to complete the hybrid control scheme. The tests were repeated to determine the achievable performance improvement. Frost build up tests at high indoor room humidity were conducted with all control schemes to determine the influence of the control scheme on frost distribution and system performance. To determine the influence of a fixed and repeatable airside maldistribution, additional tests with partially blocked evaporator coils were conducted for both units with the electronic expansion valve and hybrid control scheme.

A Review and Cost Comparison of Current Idle-Reduction Technology

As of January 1, 2008 idling of the main vehicle engine for the purpose of powering sleeper cabin amenities by any truck over 10,000 lbs (4,500 kg) within the borders of the state of California is prohibited unless strict emissions standards are met. Following California’s lead, a number of other states have also passed legislation restricting idling time and emissions. In anticipation of tighter idling legislation and rising fuel prices, idle-reduction technologies are garnering an increasing market share. These include auxiliary battery-electric power systems, primary vehicle battery systems, truck-stop electrification, diesel-fueled auxiliary power systems, and fuel-fired heaters. In this paper the current state of anti-idling technology is reviewed. Off the shelf systems are compared in an attempt to discern which is more advantageous in terms of factors such as lifetime cost, lifetime cost per hour, and payback period.Copyright

Compressor driven metal hydride heat pumps using an adsorptive slurry and isothermal compression

Metal hydrides have been investigated for use in environmentally friendly heat pumps. These systems operate using reversible adsorption and desorption of hydrogen from metallic compounds and can be incorporated in a cycle having a work input (compressor) or thermal energy input (generator). Some challenges faced by compressor driven metal hydride heat pumps are poor heat transfer in the metal hydride beds and high compressor discharge temperatures. To overcome these challenges, this article investigates the use of a metal-hydride slurry in conjunction with various isothermal compression techniques. Liquid-flooded, electrochemical, and liquid piston compressors were modeled and integrated into a system model in order to assess their impact on the performance of the slurry-based metal hydride heat pump system.

Development of a generalized steady-state simulation framework for positive displacement compressors and expanders

In this paper, a generalized framework is presented that can be used to simulate the steady-state performance of a wide range of positive displacement compressors and expanders (scroll, piston, screw, rotary, spool, etc.). The complete simulation algorithm is described, and an emphasis is placed on the numerical methods required to obtain robust behavior of the simulation. This formulation has been implemented into an open-source software package entitled PDSim written in the Python language. PDSim is the first open-source generalized compressor and expander simulation package. The source code can be freely obtained on the internet.