Developing a combined intake and exhaust vent for heat recovery ventilation in cold climates

Thesis (M.S.) University of Alaska Fairbanks, 2022Heat recovery ventilation systems have become increasingly popular in modern residential buildings, particularly in cold climates. This has led to the research and development of supporting technologies, such as combined intake/exhaust vents. Conventionally, the intake and exhaust airflows of a heat recovery ventilation system use separate vents and penetrations in a building's envelope; combined intake/exhaust vents package these airflows together and use only one penetration. This simplifies heat recovery ventilation system installation and can lead to higher operating efficiencies; the implications are reduced up-front and operating costs as well as broadened access to heat recovery ventilation. Unfortunately, in cold climates, existing combined intake/exhaust vent designs are susceptible to frost accumulation, a mode of failure. The aim of this work was to develop a combined intake/exhaust vent more suitable for cold climate use: the Arctic Dual Hood. The design was developed in iterations informed by experimentation. These experiments included climate chamber evaluations and field performance comparisons. This design process produced a functional prototype with favorable frost mitigation characteristics compared to an existing combined intake/exhaust vent design, as determined through the field performance comparisons. Additionally, this prototype observed the constraints and met the performance requirements imposed by the American Society of Heating, Refrigeration, and Air-Conditioning Engineer's Standard 62.2: Ventilation and Acceptable Indoor Air Quality in Residential Buildings.Alaska Center for Energy and Power, Cold Climate Housing Research Center, Department of Navy award N00014-19-1-2235Chapter 1. Introduction -- 1.1 Impetus -- 1.2 Background information -- 1.2.1 Ventilation in cold climates -- 1.2.2 Indoor air quality and health -- 1.2.3 Heat recovery ventilation -- 1.2.4 Combined intake and exhaust vents -- 1.2.5 Frost accumulation -- 1.2.6 Materials and manufacturing techniques -- 1.3 Thesis organization. Chapter 2. Design -- 2.1 Requirements -- 2.2 Scope of Work -- 2.3 Design Methodology -- 2.3.1 Modeling and Simulation -- 2.3.2 Physical Experimentation -- 2.4 General Form of Design -- 2.5 Prototypes -- 2.6 Supporting Components. Chapter 3. Climate chamber evaluations -- 3.1. Introduction -- 3.2. Equipment -- 3.2.1. Climate chamber -- 3.2.2. The climate chamber apparatus -- 3.2.3. Instrumentation and controls -- 3.3. Methods -- 3.4. Results -- 3.5. Discussion and conclusions. Chapter 4. Field performance comparisons -- 4.1. Introduction -- 4.2. Equipment -- 4.2.1. Installation -- 4.2.2. Instrumentation -- 4.3. Methods -- 4.4. Results -- 4.5. Discussion and conclusions. Chapter 5. Contamination evaluation -- 5.1. Introduction -- 5.2. Equipment -- 5.3. Methods -- 5.4. Results -- 5.5. Discussion and conclusions. Chapter 6. Conclusions and recommendations -- 6.1. Conclusions -- 6.2. Recommendations. References -- Appendices

Impact of Intake and Exhaust Ducts on the Recovery Efficiency of Heat Recovery Ventilation Systems

The heat recovery efficiency of ventilation systems utilizing heat recovery ventilators (HRVs) depends not only on the heat recovery efficiency of the HRV units themselves but also on the intake and exhaust ducts that connect the HRV units to the outside environment. However, these ducts are often neglected in heat loss calculations, as their impact on the overall heat recovery efficiency of HRV systems is often not understood and, to the knowledge of the authors, a mathematical model for the overall heat recovery efficiency of HRV systems that accounts for these ducts has not been published. In this research, a mathematical model for the overall heat recovery efficiency of HRV systems that accounts for the intake and exhaust ducts was derived and validated using real-life data. The model-predicted decrease in heat recovery efficiency due to the ducts was in reasonable agreement (relative error within 20%) with the real-life measurements. The results suggest that utilizing this model allows for more correct ventilation heat loss calculations compared to using the heat recovery efficiency of the HRV unit alone, but more field studies are needed to verify the accuracy of this model in a wide range of applications

Impact of Intake and Exhaust Ducts on the Recovery Efficiency of Heat Recovery Ventilation Systems

The heat recovery efficiency of ventilation systems utilizing heat recovery ventilators (HRVs) depends not only on the heat recovery efficiency of the HRV units themselves but also on the intake and exhaust ducts that connect the HRV units to the outside environment. However, these ducts are often neglected in heat loss calculations, as their impact on the overall heat recovery efficiency of HRV systems is often not understood and, to the knowledge of the authors, a mathematical model for the overall heat recovery efficiency of HRV systems that accounts for these ducts has not been published. In this research, a mathematical model for the overall heat recovery efficiency of HRV systems that accounts for the intake and exhaust ducts was derived and validated using real-life data. The model-predicted decrease in heat recovery efficiency due to the ducts was in reasonable agreement (relative error within 20%) with the real-life measurements. The results suggest that utilizing this model allows for more correct ventilation heat loss calculations compared to using the heat recovery efficiency of the HRV unit alone, but more field studies are needed to verify the accuracy of this model in a wide range of applications

Actions of compounds manipulating the nitric oxide system in the cat primary visual cortex.

1. We iontophoretically applied NG-nitro-L-arginine (L-NOArg), an inhibitor of nitric oxide synthase (NOS), to cells (n = 77) in area 17 of anaesthetized and paralysed cats while recording single-unit activity extracellularly. In twenty-nine out of seventy-seven cells (38%), compounds altering NO levels affected visual responses. 2. In twenty-five out of twenty-nine cells, L-NOArg non-selectively reduced visually elicited responses and spontaneous activity. These effects were reversed by co-application of L-arginine (L-Arg), which was without effect when applied alone. Application of the NO donor diethylamine-nitric oxide (DEA-NO) produced excitation in three out of eleven cells, all three cells showing suppression by L-NOArg. In ten cells the effect of the soluble analogue of cGMP, 8-bromo-cGMP, was tested. In three of those in which L-NOArg application reduced firing, 8-bromo-cGMP had an excitatory effect. In six out of fifteen cells tested, L-NOArg non-selectively reduced responses to NMDA and alpha-amino-3-hydroxy-5-methylisoxasole-4-propionic acid (AMPA). Again, co-application of L-Arg reversed this effect, without enhancing activity beyond control values. 3. In a further subpopulation of ten cells, L-NOArg decreased responses to ACh in five. 4. In four out of twenty-nine cells L-NOArg produced the opposite effect and increased visual responses. This was reversed by co-application of L-Arg. Some cells were also affected by 8-bromo-cGMP and DEA-NO in ways opposite to those described above. It is possible that the variety of effects seen here could also reflect trans-synaptic activation, or changes in local circuit activity. However, the most parsimonious explanation for our data is that NO differentially affects the activity of two populations of cortical cells, in the main causing a non-specific excitation

Understanding the Stable Isotope Composition of Biosphere-Atmosphere CO 2 Exchange

Stable isotopes of atmospheric carbon dioxide (CO2) contain a wealth of information regarding biosphere-atmosphere interactions. The carbon isotope ratio of CO2 (δ13C) reflects the terrestrial carbon cycle including processes of photosynthesis, respiration, and decomposition. The oxygen isotope ratio (δ18O) reflects terrestrial carbon and water coupling due to CO2-H2O oxygen exchange. Isotopic CO2 measurements, in combination with ecosystem-isotopic exchange models, allow for the quantification of patterns and mechanisms regulating terrestrial carbon and water cycles, as well as for hypothesis development, data interpretation, and forecasting. Isotopic measurements and models have evolved significantly over the past two decades, resulting in organizations that promote model-measurement networks, e.g., the U.S. National Science Foundation's Biosphere-Atmosphere Stable Isotope Network, the European Stable Isotopes in Biosphere-Atmosphere Exchange Network, and the U.S. National Environmental Observatory Network

Understanding the stable isotope composition of biosphere-atmosphere CO2 exchange

Stable isotopes of atmospheric carbon dioxide (CO2) contain a wealth of information regarding biosphere-atmosphere interactions. The carbon isotope ratio of CO2 (δ13C) reflects the terrestrial carbon cycle including processes of photosynthesis, respiration, and decomposition. The oxygen isotope ratio (δ18O) reflects terrestrial carbon and water coupling due to CO2-H2O oxygen exchange. Isotopic CO2 measurements, in combination with ecosystem-isotopic exchange models, allow for the quantification of patterns and mechanisms regulating terrestrial carbon and water cycles, as well as for hypothesis development, data interpretation, and forecasting. Isotopic measurements and models have evolved significantly over the past two decades, resulting in organizations that promote model-measurement networks, e.g., the U.S. National Science Foundation's Biosphere-Atmosphere Stable Isotope Network, the European Stable Isotopes in Biosphere-Atmosphere Exchange Network, and the U.S. National Environmental Observatory Network