Optimizing Radiant Systems for Energy Efficiency and Comfort

The technical approach will include a combination of fundamental full-scale laboratory experiments, whole-building energy simulations, development of simplified models for radiant slab system design and operation, validation of these new methods in field studies, collection of energy performance and occupant satisfaction data from a large number of buildings with radiant systems, and an update to Title-24 for radiant systems.

Project Team: CBE faculty and staff will lead the project, with support from Taylor Engineering, New Buildings Institute, TRC, and Price Industries. This team is involved in a wide range of research tasks:

Laboratory Tests

We have completed a series of full-scale laboratory experiments at two locations to provide a sound theoretical understanding of the behavior of radiant systems, as described briefly below.

Price Lab, Winnipeg, Manitoba: In September 2015 in collaboration with Price Industries and Armstrong World Industries, we conducted experiments to investigate the impact of suspended acoustical clouds and air movement on the cooling capacity of a radiant chilled ceiling. Two technical journal papers have been written about the experiments. In the first paper, Karmann et al. (2017a) found that by covering only 47% of the ceiling area with free-hanging acoustical clouds below a radiant chilled ceiling, only an 11% reduction in cooling capacity was measured while achieving acceptable sound absorption performance (see graphic abstract below). In the second paper, Karmann et al. (in press-a), it was found that with the same 47% coverage by acoustical clouds, adding a ceiling fan blowing up increased the overall cooling capacity of the radiant ceiling (compared to the ceiling with no clouds and no air movement) by 15% and adding small fans above the clouds blowing horizontally increased cooling capacity by almost 19%.

FLEXLAB, Lawrence Berkeley National Laboratory: During the summer of 2016, we conducted four full-scale experiments: (1) Impact of direct solar radiation, increased air movement, and carpet coverage on the cooling capacity of a radiant floor system; (2) Side-by-side comparison of cooling performance of radiant vs. all-air systems; (3) Pulsed flow control of radiant systems; and (4) Validation of the response time method that we described in Ning et al. (2017). Technical papers are currently nearing completion for the first three studies.

Simplified Design and Operation Tools

Results from extensive energy simulation parametric studies will provide a realistic range of radiant system configurations. We use this information to create a simplified design and operation tool for radiant slab systems, and we will implement this via a web-based tool. To date, we have developed an initial control strategy for thermally massive radiant systems that shows promising results regarding its ability to load shift, maintain comfort, and reduce energy costs. In August 2017, Paul Raftery presented a paper describing these results at Building Simulation 2017 in San Francisco (Raftery et al. 2017). We are currently developing a sequence of operations which we will test in field study sites, and which will be publicly available.

To provide additional background and context for current design practice, we interviewed eleven prominent professionals with substantial experience in the design, construction and operation of high thermal mass radiant buildings in North America. A report was written that documents the variety of design and control approaches currently used, highlighting themes and variations in common practice (Paliaga et al. 2017).

Field Studies

We are conducting detailed field studies in three field studies of radiant slab buildings, to include occupant satisfaction surveys, system monitoring, analysis of system and energy performance, and testing and demonstrating optimized control approaches. We have expanded the list to four buildings as described below:

Anaheim Regional Transportation Intermodal Center (ARTIC), Anaheim: CBE’s industry partners at Viega identified the ARTIC project as a field study site. CBE researchers conducted measurements of direct solar radiation on the chilled radiant floor system in ARTIC during October 2016. A technical report on the study is nearing completion.

Delta Products, Fremont: Delta Products agreed to provide their new headquarters as one of the field study sites. Field monitoring and energy measurements are currently ongoing.

Sacramento Municipal Utility District (SMUD) East Campus Operations Center, Sacramento: CBE completed a case study in 2015 of the SMUD building as part a research project sponsored by the California Energy Commission (CEC) Public Interest Energy Research (PIER) Program, entitled “Advanced Integrated Systems Technology Development: Personal Comfort Systems and Radiant Slab Systems.” The SMUD case study report was part of the final report to CEC and can be found as Appendix H here. As part of the current project, we will be implementing the newly developed control strategies for high thermal mass radiant systems and evaluating their impact on energy and comfort performance.

David Brower Center, Berkeley: CBE completed a case study in 2015 of the David Brower Center as part a research project sponsored by the California Energy Commission (CEC) Public Interest Energy Research (PIER) Program, entitled “Advanced Integrated Systems Technology Development: Personal Comfort Systems and Radiant Slab Systems.” The Brower Center case study report was part of the final report to CEC and can be found as Appendix G here. As part of the current project, we will be implementing the newly developed control strategies for high thermal mass radiant systems and evaluating their impact on energy and comfort performance.

Energy performance, cost assessment, and occupant surveys

CBE conducted a large outreach to identify as many buildings as possible having radiant systems, and gathered and analyzed data for energy performance and occupant satisfaction. This work is intended to provide industry with real world examples of radiant system performance in comparison to other buildings and benchmarks.

Online radiant map: As part of this task, CBE developed an expanded database of over 400 commercial buildings using radiant cooling and heating. All buildings from the database are displayed on an online interactive map located here. A report was written summarizing the results and trends from this radiant map dataset, which focuses primarily on North America (United States and Canada) (Talami et al. 2017).

Energy performance: The CBE research team was able to obtain annual energy performance data from 23 buildings in North America using radiant systems, to our knowledge, the largest database of its kind to date. A report (Higgins and Carbonnier 2017) was written summarizing the energy performance results and found that nearly all the buildings outperformed peer buildings and national benchmarks, suggesting that when radiant systems are part of an integrated design approach, they can lead to low-energy consumption.

Thermal comfort and occupant surveys: Karmann et al. (2017b) performed a literature review in 2015 to assess if radiant systems provide better, equal or lower thermal comfort than all-air systems. We found that a limited number of studies are available and therefore a solid answer could not be given at the time of publication. Nevertheless, there was suggestive evidence that radiant systems may provide equal or better comfort than all-air systems, as was determined in our subsequent more detailed study below.

As part of our efforts to document the above-described radiant building database, the research team also implemented the CBE occupant survey in 20 buildings, which added to six surveys already completed in radiant buildings. By combining the radiant surveys with previously completed surveys in all-air buildings, we were able to assemble the largest dataset, to our knowledge, used in a comparison of occupant satisfaction in radiant buildings. Karmann et a. (in press-b) presents indoor environmental quality survey results from 3,892 respondents in 60 office buildings located in North America; 34 of which used all-air systems and 26 of which used radiant systems as the primary conditioning system. The results indicate that radiant and all-air spaces have equal indoor environmental quality, including acoustic satisfaction, with a tendency towards improved temperature satisfaction in radiant buildings.

Case study briefs: As part of the large database of radiant buildings compiled for the above studies, the research team selected and completed case studies for nine commercial buildings that demonstrate good performance in terms of both energy use and occupant satisfaction. Each of these radiant case studies are available as downloadable 4-page case study briefs, as highlighted in the October 2017 issue of Centerline. Each brief includes a building and radiant system description, energy use vs. national benchmarks, and survey results for thermal comfort. Carbonnier et al. (2017) provide an overview of the nine case study briefs along with the energy performance results.

Codes and standards: We will provide updates to the Title 24 Alternative Calculation Method Reference Manual, to enable improved modeling capabilities of radiant systems. Participate on related ASHRAE Standards and Technical Committees to provide new information and guidance based on the results of the above mentioned tasks.