Development of an Outdoor Temperature-Based Control Algorithm for Residential Mechanical Ventilation Control

Abstract

Executive SummarySmart ventilation systems use controls to ventilate more during those periods that provide either an energy or IAQ advantage (or both) and less during periods that provide a disadvantage. Using detailed building simulations, this study addresses one of the simplest and lowest cost types of smart controllers-outdoor temperature-based control. If the outdoor temperature falls below a certain cut-off, the fan is simply turned off. The main principle of smart ventilation used in this study is to shift ventilation from time periods with large indoor-outdoor temperature differences, to periods where these differences are smaller, and their energy impacts are expected to be less. Energy and IAQ performance are assessed relative to a base case of a continuously operated ventilation fan sized to comply with ASHRAE 62.2-2013 whole house ventilation requirements. In order to satisfy 62.2-2013, annual pollutant exposure must be equivalent between the temperature controlled and continuous fan cases. This requires ventilation to be greater than 62.2 requirements when the ventilation system operates. This is achieved by increasing the mechanical ventilation system airflow rates.There were four steps to this analysis:1. The outdoor temperature cut-offs were calculated-either as a fixed temperature (5°C), a fixed percentile (Q25 th ) 1 2. The REGCAP simulation tool was used to estimate the energy savings and IAQ impacts of using these cut-offs to control a mechanical exhaust fan. The simulated fans were not oversized and not compliant with 62.2-2013., or based on infiltration estimates (Inf and Inf2) using the stack part of the enhanced ventilation model (AIM-2) in the ASHRAE Handbook of Fundamentals.3. Exhaust fans were resized to maintain equivalence with 62.2-2013 using an iterative optimization procedure that incorporated both the stack and wind parts of the AIM-2 ventilation model. 4. The REGCAP simulation tool was used to calculate energy use and relative exposures, using oversized fans that provided equivalence with 62.2-2013.As shown in the figure below, new and existing, single-and two-story test homes from 10 to 3 ACH50 had substantial energy savings from the control of ventilation systems based on outdoor temperature, while maintaining equivalence with ASHRAE 62.2-2013 through fan oversizing. These savings reflect the maximum energy reduction estimate of the four temperature cut-off types (5°C, Q25 th , Inf and Inf2), for each combination of climate zone, airtightness, stories and house age. Limited savings were realized in milder climates for tighter homes of 1.5 ACH50. Temperature control is not recommended in climate zone 1 or in 0.6 ACH50 cases. In most cases, savings were greatest in 3 and 5 ACH50 homes. Annual HVAC energy 1 25 th percentile of annual hourly temperatures from TMY3 data files.iii savings ranged from approximately 100 kWh to 4,000 kWh (0.1 to 6% of total HVAC energy use). Absolute energy reductions generally increased with climate severity, though percentage savings were more consi...

Development of Smart Ventilation Control Algorithms for Humidity Control in High-Performance Homes in Humid U.S. Climates

“…So, the system was effectively able to control to seven discrete hourly average mechanical ventilation rates, from 0 to 300% of 62.2-2013, by 50% increments (each representing 10-minutes of runtime in the hour). As was found by Less et al (2014), larger ventilation fans increase the ability to engage in smart control strategies, while maintaining annual equivalence. For this reason, the CFIS system provides an excellent opportunity for smart ventilation control, though its energy use is typically greater due to use of the central air handler fan for distribution.…”

“…Acceptable IAQ is defined as providing annual pollutant exposure equivalent to a continuously operated ventilation fan sized to ASHRAE Standard 62.2-2013. Smart ventilation strategies have been previously applied to energy conservation and peak demand reduction using time-based controls as well as sensors for other ventilation fans (Max H. Sherman & Walker, 2011), and based on indoor/outdoor temperatures (Less, Walker, & Tang, 2014). The same principles will be applied in this study for humidity control.…”

Smart Ventilation for Advanced California Homes – Single Zone Technology Task

“…It may be possible to achieve greater energy savings if an additional level of complexity is added onto the Seasonal control. Past work on temperature-controlled smart ventilation suggested that a simple cut-off temperature was an effective approach to reducing ventilation load through smart control (Less et al, 2014). In this work, we developed a cut-off approach that ensures annual relative exposure less than one using a weighted average approach.…”

“…Past work on temperature controlled smart ventilation suggested that a simple cut-off temperature was an effective approach to reducing ventilation load through smart control (Less et al, 2014). In this work, we developed a more complicated cut-off approach that ensures annual relative exposure less than one using a weighted average approach and parametric optimization (as in the Seasonal controller).…”

“…A controller named RIVEC (short for Residential Integrated Ventilation Controller) was developed and briefly fieldtested in California that used occupancy, auxiliary fan sensing, grid signals and timer-based temperature controls (Iain S. Walker, Sherman, & Dickerhoff, 2012). Less, Walker, & Tang (2014) studied the effects of several temperature-based control strategies that used cut-off temperatures below which IAQ fans were turned off (fan airflow were increased during all other hours). Smart controls for humidity control in hot and warm-humid climates were developed for similar homes in Less, Walker, & Ticci (2016).…”