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Designers and operators typically do not include distribution losses when analyzing the performance of heating hot water systems. Though these losses are very small compared to design-day loads, they are not zero. As the losses occur continuously whenever the systems operate, and these systems spend the vast majority of time operating at low part loads, the losses can still comprise a substantial fraction of annual heating energy consumption. When the entire building requires heating, these distribution losses have little negative effect. However, the losses unnecessarily waste heat whenever the air handlers operate above minimum outside air. In warmer weather, when temperatures are above air handler economizer lockout conditions, the losses are doubly detrimental as they both waste heat and increase cooling plant loads. We reviewed the literature and could not find measurements of hot water distribution losses in real buildings. Here, we report results from 7 large commercial buildings at 5 different organizations, all located in California, climate zones 3B and 3C. For each building, we commanded the valves closed on heating hot water end-use components and shut down the air handlers. We operated the heating hot water system to maintain a constant flow and a constant hot water supply temperature setpoint typical for each building. We then measured the steady-state heating power required to maintain that setpoint. Building characteristics varied widely in terms of size (5,100-15,000 m² or 55,000-160,000 ft²), type (e.g., city administrative office, college lab and classroom), HVAC design (VAV reheat or dual duct systems), and year of construction (1917-2000). Despite this, the results were reasonably consistent when normalized to building conditioned floor area. The median loss rate was 1.2 W/m² (0.37 BTU/hr.ft²) with a min/max range of 0.8 - 2 W/m² (0.25 - 0.63 BTU/hr.ft²) across all buildings at typical supply temperatures for each building. For comparison, this is roughly a third of average office plug loads, and though it is low on a conditioned floor area basis, it ranged from 6% to 60% of the annual HW energy consumption for the five buildings for which we had long term data. We discuss the methods, buildings, and results in more depth in this paper, as well as the opportunities for improving system design and operation. [ABSTRACT FROM AUTHOR]

Evaporative cooling technologies have the potential to dramatically reduce electrical energy consumption in hot and dry climates. A Sub-Wet bulb Evaporative Chiller (SWEC) can chill water to temperatures lower than wet bulb of outdoor air, making it desirable for cooling applications, similar to M-cycle indirect evaporative air coolers. However, the exiting water temperature from the SWEC is still significantly higher than that produced by a vapor compression unit. Hence, in order to effectively utilize this technology, it needs to be coupled with a high-effectiveness water-to-air heat exchanger. In this paper, a validated model of a SWEC, developed in prior work, is coupled with that of a counter-flow Microchannel Polymer Heat eXchanger (MPHX), currently being developed by the group. The SWEC is able to achieve sub-wet bulb temperatures via the configuration of four evaporative media sections sandwiched between four cross-flow air-to-air heat exchangers. An effectiveness-Number of Transfer Units (NTU) approach is used to model the SWEC. A sectional model for the MPHX, which includes potential for condensation in the air stream along the heat exchanger length as it is cooled by the chilled water, is developed. The two component-level models are coupled together to determine the system-level performance. The tradeoff between cooling capacity, system COP, and MPHX exit air temperature is discussed for a typical outdoor summer condition in California climate zone 12. [ABSTRACT FROM AUTHOR]

Anyone who has had the opportunity to work in the Controlled Environment Agriculture (CEA) industry knows that managing the latent load of an operation is paramount to its success. For a plant to grow and thrive, it must pull water and nutrients from the growing medium, through its roots and up its stem to eventually transfer the nutrients into its growing tissue. To complete the process, this internal water must finally be exposed to the open air so it can evaporate away. A CEA facility is a farm operation that is fully contained indoors where light, temperature, relative humidity, and the atmosphere can be controlled. Most cannabis CEA facilities introduce supplemental carbon dioxide to encourage plant growth. Because of this, the grow rooms are sealed with minimal to no outside air to prevent exhausting valuable carbon dioxide. If latent removal capacity is insufficient, the relative humidity in the space quickly reaches saturation levels and the plant can no longer move water from roots to air. This can cause serious plant health issues that can eventually lead to death of the plant. Every pint of water placed in the growing medium that does not drain to waste outside the room must, eventually, be removed from the air. Sensible loads in a CEA operation are fairly easy to determine and handle due to the large lighting loads (20 – 50 watts/ft² ), but when the lights go off, it’s a different story. During the simulated nighttime, the plants reduce the amount of water they deliver to the air, but it does not disappear. Without the sensible load of the lighting system to drive the latent capacity of air conditioning, dedicated dehumidification must be used to control relative humidity. A high efficiency dehumidification system is vital to minimize the total electric consumption of the operation. This paper explores a comparative energy analysis of various dehumidification technologies used in CEA operations. The primary systems to be examined will be integrated HVAC systems with on-site heat recovery to achieve dehumidification reheat, chilled water systems with on-site heat recovery to achieve dehumidification reheat, solid or liquid desiccant dehumidification systems, and high efficiency stand-alone dehumidifiers as defined by California’s Title 24 proposed regulations for dehumidification efficiency in CEA facilities. Title 24 is a code for CEA facilities that governs dehumidification efficiency, lighting efficiency, and requirements for greenhouses. When possible, minimum allowed efficiencies and actual equipment efficiencies will be used. This analysis will focus on CEA cannabis operations, but the results could be applied to other crops, as well. [ABSTRACT FROM AUTHOR]

Insulated ducts are extensively used for building air-conditioning applications. The insulation levels are designed based on energy loss considerations while the level of insulation required to prevent condensation on the duct surface from the air surrounding the duct is often not evaluated. In this paper, a coupled heat-mass transfer model has been developed to model the condensation-evaporation on vertical duct surfaces with for ducts within stud-bays (cavities) located adjacent to the conditioned building envelope. California Building Energy Code Compliance-Residential (CBECC-Res) building simulation tool was used to calculate the indoor space conditions for a single-family home located in sixteen different Climate Zones (CZ) of California. The simulations indicated that an increase in the area available for air infiltration in the cavity can increase condensation, however, the duration for which condensed water is present on the duct decreases. The quantity of water condensed on uninsulated ducts with low emissivity surfaces (ε close to zero) is much higher than that for high emissivity (ε=0.9) ducts (twice as high for reference CZ 13, Fresno). Furthermore, insulating the duct reduced condensation significantly and for CZ 13, R-1 insulation is sufficient to eliminate condensation completely. The worst-case scenario (low emissivity, uninsulated duct in a cavity with a large area for infiltration) was modeled for all climate zones. The climate zone with the highest level of condensation is CZ 9 (Burbank) i.e. 0.0081 lb. (0.037 kg), while the condensation was lowest for CZ 2 (Santa Rosa). Overall, the amount of water condensed, even in the worst-case scenario, is small compared to the moisture already present in the wooden studs surrounding the duct. [ABSTRACT FROM AUTHOR]

Insulated ducts are extensively used for building air-conditioning applications. The insulation levels are designed based on energy loss considerations while the level of insulation required to prevent condensation on the duct surface from the air surrounding the duct is often not evaluated. In this paper, a coupled heat-mass transfer model has been developed to model the condensation-evaporation on vertical duct surfaces with for ducts within stud-bays (cavities) located adjacent to the conditioned building envelope. California Building Energy Code Compliance-Residential (CBECC-Res) building simulation tool was used to calculate the indoor space conditions for a single-family home located in sixteen different Climate Zones (CZ) of California. The simulations indicated that an increase in the area available for air infiltration in the cavity can increase condensation, however, the duration for which condensed water is present on the duct decreases. The quantity of water condensed on uninsulated ducts with low emissivity surfaces (ε close to zero) is much higher than that for high emissivity (ε=0.9) ducts (twice as high for reference CZ 13, Fresno). Furthermore, insulating the duct reduced condensation significantly and for CZ 13, R-1 insulation is sufficient to eliminate condensation completely. The worst-case scenario (low emissivity, uninsulated duct in a cavity with a large area for infiltration) was modeled for all climate zones. The climate zone with the highest level of condensation is CZ 9 (Burbank) i.e. 0.0081 lb. (0.037 kg), while the condensation was lowest for CZ 2 (Santa Rosa). Overall, the amount of water condensed, even in the worst-case scenario, is small compared to the moisture already present in the wooden studs surrounding the duct. [ABSTRACT FROM AUTHOR]