Seminar 49 -- Direct Expansion Ground Source Heat Pump: Reviewing Issues, Advancements and Advantages

Track: HVAC&R Systems and Equipment
Sponsor: 6.8 Geothermal Heat Pump and Energy Recovery Applications
Chair: Xiaobing Liu, Ph.D., Member, ORNL, Oak Ridge, TN
Direct expansion ground source heat pump (DX-GSHP) technology uses refrigerant as primary working fluid in ground heat exchangers (GHE). It is the oldest type of ground coupled heat pump and potentially the most efficient vapor compression-based air conditioning systems that are not commonly used due to several design and operational issues. This seminar covers the history and status of DX-GSHP, operational issues, ongoing studies on trends in GHE design and use of natural refrigerants and common myths surrounding DX-GSHP technology.

1. Performance and Reliability of Direct-Expansion Ground-Coupled Heat Pumps
Demba Ndiaye, Ph.D., P.E., BEMP, Member, University of North Carolina at Charlotte, Charlotte, NC
Direct Expansion Ground-Coupled Heat Pumps are potentially the most efficient vapor compression-based air conditioning system, but are not very popular due to the numerous operational and design issues they are plagued with: shortage of field studies, oil return to the compressor, expansion valve hunting, refrigerant flow mal-distribution in parallel loops, high pressure drops and gains in the ground heat exchanger, variable speed operation of the compressor, lack of reliable numerical models of the ground heat exchanger and of the whole system and lack of generalized design guidelines. This seminar discusses these issues and possible solutions to them.

2. Status and Trends in DX Bore Field Dimensioning
Louis Lamarche, Ph.D., Ecole de Technologie SUperieure, Montreal, QC, Canada
In a classical Secondary Loop (SL) GSHP, the ground loop is sized independently and simply to exchange enough heat with the ground. In a DX system however, the ground loop is an integral part of the heat pump and clear design metrics is less obvious. Therefore, good design can become technology-dependant and other constraints like oil-return or valve hunting plays a role as much as thermal performance. Recent research has brought some new guidelines to improve global knowledge on this technology. This presentation discusses recent trends in ground loop design based on experimental observations and theoretical modeling.

3. Direct Expansion Ground Source Heat Pump Using Carbon Dioxide As Refrigerant
Parham Eslami Nejad, Ph.D., Natural Resources Canada, Varennes, QC, Canada
Although the detrimental environmental impacts of conventional refrigerants have raised global concern, due to the worldwide growing energy demand, high energy efficiency of heat pumps still remains a great incentive for using this technology in residential and commercial buildings. Over the last decade, several studies have been conducted to replace synthetic refrigerants with natural ones. Among the candidates, CO2 has been attracting more attention due to being environmentally benign and safe together with superior heat transfer characteristics. This seminar presents some field operation results, modeling advancements and system and GHE performance improvements of DX-GSHP using CO2 as refrigerant.

Presented: June 28, 2017, 8:00-9:30 AM
Run Time: 90 min.

This is a zip file that consists of PowerPoint slides synchronized with the audio-recording of the speaker (recorded presentation), PDF files of the slides, and audio only (mp3) for each presentation.