Handbook Expands on GSHP Tech Info

From eSociety, February 2019

New users will be able to more easily find the information they are looking for in Chapter 34, Geothermal Energy, in the 2019 ASHRAE Handbook—HVAC Applications.

The chapter was rearranged to put the ground-source heat pump content before the direct use material, which was done based on how the material is being used in the field, said Harrison Skye, Ph.D., Associate Member ASHRAE, who was the Handbook co-subcommittee chair for TC 6.8, Geothermal Heat Pump and Energy Recovery Applications.

“GSHPs are more widely used, so we decided to put it first,” said Skye, who is a mechanical engineer at the National Institute of Standards and Technology and TC 6.8’s program committee chair.

The chapter has a number of revisions, updated code references and housekeeping refreshes such as new headings. The chapter now groups related material together that was previously separated, he said.

TC 6.8 added two new sections to the GSHP material: direct exchange systems and pressure considerations for deep boreholes. There were no changes to the direct use material, said Skye.

The direct exchange systems section includes background and introductory material about the technology that has relatively small market share but has potential to grow, said Skye. The TC wanted to include basic material in this Handbook to give background information and provide a base for future revisions of the handbook that can include more detailed design guidance, he said.

Before the 2019 edition, Chapter 34 did not have information on how to provide for pressure considerations for deep boreholes. Skye said there are special considerations for deep boreholes because hydrostatic pressure can be so large, engineers have to carefully select the right tubes so they will not burst.

A major update to the chapter will help people calculate their long-term temperature penalties for a wider range of configurations, said Skye.

The chapter’s primary design method was updated to include the calculation of the long-term temperature penalty using equations, rather than using values from a table as was done in previous editions. The newly added equations and the previously provided tables use the same concentric cylinder source method.

In previous chapters, people used one table to estimate the long-term temperature penalty. Skye said the table didn’t cover all configurations, so it was replaced by the calculation method used to generate those tables.

“The answers are the same. Now, by doing a little bit more calculation, people can get numbers for their temperature penalties for a wider variety of ground borefield configurations,” he said.

Smaller updates to the chapter include material in the standing column wells, hybrid systems, grout, water wells and cost data sections. Code listings were updated, including references to ANSI/CSA/IGSHPA Standard C448-16 (2016) and IMC 2015, he said.