The need for cooling in buildings is mainly handled using systems based on the refrigeration cycle, often an energy- and cost-intensive process. High thermal mass radiant systems (HTMR) enable the use of warmer than typical chilled water temperatures to provide cooling. In favorable weather conditions, the cooled water can be produced through low-energy and low-cost cooling devices. In this two-phased study, we first determined the warmest supply water temperature (SWT) needed in HTMR that maintains thermally comfortable conditions on the cooling design day. Then, we investigated the potential of replacing the refrigeration cycle with evaporative cooling devices in the primary cooling system. We performed a quasi-random sampling of building and HTMR system design parameters representing typical building characteristics and design cooling loads for lighting, people, and plug loads to create 360,900 single zone EnergyPlus models. We iteratively simulated the models on the climate zones’ cooling design day to find the warmest SWT that did not exceed a maximum zone operative temperature of 26 °C. The test cases include simulations using 14 ASHRAE and 16 California climate zones. The results show that HTMR can use SWT of 12.3, 18.2, and 21.1 °C for the 25th, 50th, and 75th percentile, respectively, of test cases, indicating that overall cooling energy and costs can be reduced in all US climates through high-temperature cooling. In addition, high-temperature cooling allows at least 40% of waterside economizer operation during the cooling season for 21 out of 30 climate zones with reasonably performing evaporative cooling devices.
High thermal mass radiant systems as a hydronic thermal mass activation method have many opportunities for cost-effective demand management. The system is regarded with the possibility of long-term transferring peak heating and cooling loads to off-peak hours and peak load reductions. This study conducted over 300,000 case calculations for a sensitivity analysis of load shifting parameters in radiant space conditioning systems across 16 climate zones in California, 14 different climatic cities outside California. The parameters analyzed include building geometric parameters (building length, width, window-to-wall ratio, orientation), internal heat source levels (from people, lights, plugs), control parameters (start and stop times), and the design construction of radiant terminals. A comparative analysis was also conducted across cities in different climatic conditions to explore the impact of climate on the load shifting capabilities of radiant space conditioning. The results of this study will aid in the formulation of strategies and the optimization design for load shifting in radiant cooling systems.
A number of operational issues exist with typical variable air volume (VAV) reheat terminal units. These include temperature stratification at the heating coil discharge and the reduced capacity and higher flow rates required for increasingly popular low temperature hot water systems. This article summarizes the findings of a recent research project that sought to better understand and help overcome these issues.
There is an increasing focus on the time at which energy is used in buildings both to reduce utility costs and carbon emissions in response to time-dependent grid signals. One method to shift electrical load out of peak pricing hours is to use batteries, but they have high first costs and also incur an energy penalty due to round trip efficiency and other losses. Another method is to use thermal storage to offset heating and cooling. Similarly, mechanical ventilation systems can also be controlled to shift energy use to periods of the day with lower energy, cost, and environmental impacts by varying the ventilation rate while still meeting ventilation code requirements. Mechanical ventilation systems in large multi-family residential buildings are mostly central air systems with either manually balanced dampers or constant airflow regulator (CAR) dampers that aim to provide a constant ventilation airflow rate to each apartment. ASHRAE 62.2 allows for dynamic ventilation rate systems in these buildings as long as the average relative exposure rate and the peak relative exposure rate during occupied periods are no more than 1 and 5, respectively, for any time interval that cannot exceed an hour. In this study, we used EnergyPlus simulations to examine energy end-use profiles for a large multi-family building under design in San Jose, California. We considered a balanced ventilation system using a central dedicated outdoor air supply (DOAS) system. We tested different load-shifting scenarios with multiple parameters to explore how the ventilation airflow rate can be varied to shift load, while also assessing energy and utility cost impacts. The parameters we assessed in each scenario were: the presence of a centralized ERV system or not; ventilation design sizing; and length of load shifting time period. All dynamic ventilation cases, with and without ERV systems, resulted in energy and operational cost savings relative to the constant ventilation cases when compared to providing the same amount of load shifting using batteries, and all tested strategies met ASHRAE 62.2 requirements. The results show that after accounting for the battery penalty typically associated with load shifting, all dynamic ventilation cases reviewed result in improved energy savings when compared to the constant ventilation strategy.
Conventional wisdom and standard industry practice is to setback zone temperature setpoints when commercial buildings are unoccupied at night. The HVAC systems then operate in warmup mode to recover zone temperatures prior to the start of occupancy, sometimes with an optimal start algorithm. These strategies were intended to reduce HVAC energy consumption when originally developed decades ago but are due for re-examination given the significant changes in HVAC systems that have since occurred. In particular, the changes currently underway with the movement toward electrification present new design considerations and priorities. Warming up a building as fast as possible may not be the best strategy in terms of energy use, operating cost, or carbon emissions. This article discusses some of the downfalls of conventional morning warmup practices, suggests an improved strategy, and shows the results from a pilot field demonstration test.
We studied a combination of heating system measures in two large commercial officebuildings in San Francisco (110,000 and 120,000 ft 2 respectively) within a project funded by the California Energy Commission’s Public Interest Efficiency Research program. We retrofitted theexisting heating plants and updated the HVAC controls to ASHRAE Guideline 36-2021 as closely as possible while retaining the existing controller hardware. These measures decreased annual natural gas consumption by about 70 percent while also reducing HVAC electricity consumption. The results reinforce previous work showing significant natural gas reductions in 3 other buildings that underwent full controls retrofits (including controller hardware), and large savings from another 3 buildings that underwent partial controls upgrades. We show that on today’s electricity grid, which is quite dirty during the winter and early morning hours when most heating occurs, the carbon emissions reduction from these measures exceeds the reduction from fully electrifying the existing heating system’s load with today’s air-to-water heat pumps. More importantly, these solutions are mutually beneficial. Acknowledging that we also need to electrify HVAC loads to meet our climate goals, replacing controls first will reduce the size, weight, first cost, and ongoing operating cost of the subsequent heat pump installation requiredto fully electrify, and will make it more feasible to do so. This paper highlights an overlooked opportunity for enormous decarbonization in the existing commercial building stock using a solution that is available, cost effective, and scalable. We should prioritize these measures first,and then electrify, rather than focusing solely on electrification.
Natural gas combustion to serve space heating hot water systems causes approximately one third of large commercial building energy use in California. This project evaluated an innovative set of non-proprietary, cost-effective methods to reduce energy consumption and associated emissions from these systems. The project demonstrated 70% natural gas savings and substantial electricity savings in two large office buildings, yielding total utility cost savings of approximately $110,000 (or $0.5/ft²) per year. The project also conducted detailed studies on distribution losses and boiler efficiency in several buildings; measured performance of key components in laboratory tests; gathered and analyzed data from hundreds of buildings to evaluate actual performance of these systems; and provided a public dataset to inform future retrofits, research, and code development. The research also highlighted characteristics that make a building a good candidate for retrofit so these results can be scaled. Market transformation activities included 10 journal and conference publications, policy recommendations and a design guide. Based on these findings and other recent work, the opportunity for similarly large emissions reductions appears to be common within the existing large commercial building stock. The resources provided by this project can aid stakeholders in achieving California’s goals to decarbonize buildings.
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