A Modeling Approach to Characterize the Demand Flexibility of the Air Distribution System in Commercial Buildings

Commercial VAV systems have been a studied as potential flexible power consumption resources to provide these services. A significant limitation is the development of control oriented models for these systems that accurately control power consumption across timescales. To this end, we develop a modeling approach that characterizes the demand flexibility of the air distribution system in commercial buildings. The model maps all feasible terminal zone damper configurations to power consumption by identifying a system resistance model connected to a pressure-flow model of the supply fan. Under this model structure, the operational range of an installed system can be quantitatively bounded by the extreme resistance curves the air distribution system encounters. We also propose a simplified control algorithm that leverages this model structure to emulate a demand flexibility event. We validate this approach by calibrating a model in an experimental testbed and additionally testing the results in a simulation environment. A brief discussion of important properties and observations that can be derived from this approach as well as avenues for improvements is presented

Optimizing Radiant Systems for Energy Efficiency and Comfort

Radiant cooling and heating systems provide an opportunity to achieve significant energy savings, peak demand reduction, load shifting, and thermal comfort improvements compared to conventional all-air systems. As a result, application of these systems has increased in recent years, particularly in zero-net-energy (ZNE) and other advanced low-energy buildings. Despite this growth, completed installations to date have demonstrated that controls and operation of radiant systems can be challenging due to a lack of familiarity within the heating, ventilation, and air-conditioning (HVAC) design and operations professions, often involving new concepts (particularly related to the slow response in high thermal mass radiant systems). To achieve the significant reductions in building energy use proposed by California Public Utilities Commission’s (CPUC’s) Energy Efficiency Strategic Plan that all new non-residential buildings be ZNE by 2030, it is critical that new technologies that will play a major role in reaching this goal be applied in an effective manner. This final report describes the results of a comprehensive multi-faceted research project that was undertaken to address these needed enhancements to radiant technology by developing the following: (1) sizing and operation tools (currently unavailable on the market) to provide reliable methods to take full advantage of the radiant systems to provide improved energy performance while maintaining comfortable conditions, (2) energy, cost, and occupant comfort data to provide real world examples of energy efficient, affordable, and comfortable buildings using radiant systems, and (3) Title-24 and ASHRAE Standards advancements to enhance the building industry’s ability to achieve significant energy efficiency goals in California with radiant systems. The research team used a combination of full-scale fundamental laboratory experiments, whole-building energy simulations and simplified tool development, and detailed field studies and control demonstrations to assemble the new information, guidance and tools necessary to help the building industry achieve significant energy efficiency goals for radiant systems in California

Concept, design and energy simulation of a Net Zero Energy Home for the Mediterranean climate

Tese de mestrado integrado em Engenharia da Energia e do Ambiente, Universidade de Lisboa, Faculdade de Ciências, 2020Para reverter os efeitos das alterações climáticas e projetar um futuro sustentável, o setor da energia está a tomar três principais medidas: eletrificação, descarbonização e eficiência energética. Entre os três maiores consumidores de energia, logo maiores emissores de carbono, encontra-se o setor dos edifícios que, especialmente no sul da Europa, avança a passos lentos no sentido do edifício eficiente, estando em fase de desenvolvimento muito precoce da implantação do edifício de alta performance. Prevê-se que os climas temperados de latitudes médias sejam dos mais afectados pelo aquecimento global, com aumento nomeadamente da frequência, duração e intensidade das ondas de calor, pelo que perceber e instalar estratégias passivas de arrefecimento é urgente. São elas: a ventilação nocturna, a obstrução solar (sombreamento), o isolamento – desde que não exceda a capacidade do espaço de evacuar calor, acumulando-o –, trocas radiativas com o céu, convectivas, evapo-transpiração, o uso da inércia para armazenamento e modelação das condições interiores em parceria com a ventilação natural para remoção do calor, etc. Um desses climas com previsão de alargamento do verão é o clima Mediterrânico, que se traduz como um clima temparado quente – classe ‘C’ na classificação climática de Köppen-Geiger – de verão seco – subclasse ‘s’ – e quente ou ameno – subtipos ‘a’ e ‘b’, portanto Csa e Csb. Para uma recolha de 68 localidades do sul da Europa, com subtipos climáticos Csa e Csb, foi feita uma análise da temperatura ambiente e radiação global horizontal. A cidade que mais se aproximava da média da amostra em ambos os parâmetros era a de Nice, no sul de França, pelo que Nice foi escolhida como a cidade representativa da norma do clima Mediterrânico e o local de construção hipotética da casa projetada nesta dissertação. Nice apresenta clima Csa e verões quentes de Junho a Setembro. A planta da moradia foi desenhada em SketchUp considerando uma família de 4 pessoas, um só piso, e uma otimização do uso dos espaços a Sul. Assim, os quartos das crianças, a sua casa-de-banho, e o solário/marquise junto à sala foram inseridos na fachada Sul. A suite dos pais foi posicionada virada a Este com o seu WC privativo no canto nordeste da casa, protegendo a envolvente da suite a Norte. Os quartos encontram-se todos na secção Este da casa. Do outro lado, a cozinha está virada a Norte, seguida da sala de jantar+sala de estar (zona DLIV) no meio da secção com janela a Oeste, e então o solário com portas de vidro amovíveis (viradas para a sala) orientado a Sul. Uma pála horizontal exterior foi dimensionada analiticamente para que sombreasse totalmente a janela do solário e quartos das crianças (têm a mesma altura) no verão, e garantisse exposição solar total no inverno. A zona térmica da cozinha teve que ser separada da da sala pois, ao contrário da última, não tem operação AVAC; no entanto, um conceito aberto moderno era desejado, pelo que se criou uma porta interior ocupando (praticamente) toda a parede de interseção entre as zonas, e definiu-se esta porta dentro do EnergyPlus, o software de simulação energética utilizado, como estando sempre aberta. A casa tem grande área envidraçada, pé-direito de 3 m, e áreas de chão bastante razoáveis. A envolvente térmica que a compõe foi baseada na de uma casa certificada Passive House Premium localizada não muito longe de Nice (em Solliès-Pont). Os isolantes térmicos foram todos trocados por cortiça de condutividade 0.04 W/m.K, um material muito produzido no sul da Europa. A composição de cada fachada foi simplificada e os coeficientes de tranferência de calor (U-values) relaxados, excepto para o telhado plano que manteve 25 cm de isolamento. A janela escolhida foi dupla de baixa emitância térmica e preenchida com Árgon. Na construção do solo, uma simplificação foi utilizada que estabelece que as temperaturas do solo a 2 m de profundidade podem ser usadas no EnergyPlus como condição de fronteira do chão, se se projectar uma construção do pavimento com 2 m de espessura, tendo-se incluído o material ‘solo’ com a espessura em falta, 1.4 m. Já no EnergyPlus, para que a janela larga da cozinha virada a Norte ventilasse a sala, motivo pelo qual ela foi traçada, foi criado um modelo de movimentação de ar multizona, o ‘Airflow Network’ (AFN). Mas tanto os controlos de abertura de janelas para ventilação natural do AFN, como de operação dos dispositivos de sombreamento amovíveis – estores exteriores e persianas interiores – foram personalizados com detalhe usando o ‘Energy Management System’ (EMS). Programando dentro do EnergyPlus, escrevendo códigos curtos e simples, as condições de controlo limitadas do software são ignoradas e sobrepostas. Assim, um modo de condicionamento híbrido de AVAC e ventilação natural foi criado, que tendo ambas as opções disponíveis ao mesmo tempo, garante que não há simultaneidade de operação entre elas, bem como um programa de controlo dos sombreamento amovível das janelas exteriores, que permite que haja um segundo dispositivo na mesma janela; tal foi feito impondo uma mudança da construção da janela para uma que inclui o estor na posição exterior, quando as suas condições de operação são satisfeitas. O estor funciona como isolamento amovível, prevenindo arrefecimento excessivo e sobraquecimento quando a casa está desocupada. As persianas interiores também são controladas no mesmo program de EMS para bloquearem a radiação directa quando: a família está em casa, a sala está perto do sobreaquecimento e a radiação incidente tem uma intensidade superior a 150 W/m2. Todos estes controlos resultaram em cargas térmicas anuais de 3.62 kWh/m2.a e 2.90 kWh/m2.a por Área Tratada (TFA, soma das áreas de todas as zonas condicionadas) para aquecimento e arrefecimento, respectivamente, portanto muito abaixo do requisito do standard Passive House de 15 kWh/m2.a para cada carga. Uma bomba de calor teórica de eficiência global de 20% foi usada como equipamento AVAC, e uma série de sete módulos fotovoltaicos foi suficiente para suprir o consumo anual total de electricidade da casa de 1.99 MWh. As horas de operação das janelas, estores e persianas foram constatadas como elevadas, evidenciando a eficiência da aplicação destas estratégias passivas – excepto para as persianas, como se previa, visto que estas bloqueiam radiação excessiva quando a casa está ocupada, e à semana a família só chega às 18:30, quando a radiação já não é elevada; estas persianas são úteis ao fim-de-semana. No entanto, verificou-se um consumo de arrefecimento elevado na sala, e taxas de desconforto por sobreaquecimento quando a casa está ocupada acima do desejado. O modo passivo revelou menor desconforto térmico, o que valida que o problema terá estado na operação do AVAC. O horário de operação intermitente deve ser demasiado reduzido, a meia hora que antecede a chegada da família a casa e em que o sistema liga será insuficiente para colmatar sobreaquecimentos. De qualquer forma, um edifício de baixíssimo consumo foi alcançado.A single-family single-floor detached NZEH was designed for the city of Nice, France, of Mediterranean climate. A horizontal overhang was projected analytically to completely shade the South glazing on summer and assure total exposure on winter. The thermal envelope was based on a nearby certified Passive House Premium, with some relaxation of the heat transfer coefficient, except for the roof (25 cm of cork insulation). An intermittent operation was used for the HVAC. A modern open concept of kitchen-dining-living room was applied, with separation of the untreated kitchen from the dining-living room (DLIV) by an always open door that covers the whole joint wall. A sunroom faces South, DLIV is in the middle (West glazing), the kitchen on the North with a wide window specifically to provide north winds for night flushing of DLIV. Thus, a multizone Airflow Network was created on EnergyPlus (E+). Both venting and movable shading devices’ operation controls were customised using EMS. By writing simple codes inside E+, its limited control conditions were overridden, enabling a hybrid conditioning mode with HVAC and natural ventilation available at the same time but never overlapping, and a second shading device on windows, the external shutter, through a full window construction change. The shutters act as movable insulation, preventing overcooling and overheating when the house is unoccupied. The internal blinds, that block beam radiation when the occupants are home, were also optimised with EMS. All these controls resulted in thermal loads below 4 kWh/m2.y per Treated Floor Area for both cooling and heating, well below the Passive House 15 kWh/m2.y threshold for each. A theoretical heat pump was used, and a string of 7 PV modules was sufficient to supply the 1.99 MWh annual total electric consumption

Responsive Building Envelope for Grid-Interactive Efficient Buildings – Thermal Performance and Control

The building sector accounts for 30% of total energy consumption worldwide. Responsive building envelopes (or RBEs) are one of the approaches to achieving net-zero energy and grid-interactive efficient buildings. However, research and development of RBEs are still in the early stages of technologies, simulation, control, and design. The control strategies in prior studies did not fully explore the potential of RBEs or they obtained good performance with high design and deployment costs. A low-cost strategy that does not require knowledge of complex systems is needed, while no studies have investigated online implementations of model-free control approaches for RBEs. To address these challenges, this dissertation describes a multidisciplinary study of the modeling, control, and design of RBEs, to understand mechanisms governing their dynamic properties and synthesis rules of multiple technologies through simulation analyses. Widely applicable mathematical models are developed that can be easily extended for multiple RBE types with validation. Computational frameworks (or co-simulation testbeds) that flexibly integrate multiple control methods and building simulation models are established with higher computation efficiency than that using commercial software during offline training. To overcome the limitations of the control strategies (e.g., rule-based control and MPC) in prior research, a novel easy-to-implement yet flexible ‘demand-based’ control strategy, and model-free online control strategies using deep reinforced learning are proposed for RBEs composed of active insulation systems (AISs). Both the physics-derived and model-free control strategies fully leverage the advantages of AISs and provide higher energy savings and thermal comfort improvement over traditional temperature-based control methods in prior research and demand-based control. The case studies of RBEs that integrate AISs and high thermal mass or self-adaptive/active modules (e.g., evaporative cooling techniques and dynamic glazing/shading) demonstrate the superior performance of AISs in regulating thermal energy transfer to offset AC demands during the synergy. Moreover, the controller design and training implications are elaborated. The applicability assessment of promising RBE configurations is presented along with design implications based on building energy analyses in multiple scenarios. The design and control implications represent an interactive and holistic way to operate RBEs allowing energy and thermal comfort performances to be tuned for maximum efficiency

Policy Design for Controlling Set-Point Temperature of ACs in Shared Spaces of Buildings

Air conditioning systems are responsible for the major percentage of energy consumption in buildings. Shared spaces constitute considerable office space area, in which most office employees perform their meetings and daily tasks, and therefore the ACs in these areas have significant impact on the energy usage of the entire office building. The cost of this energy consumption, however, is not paid by the shared space users, and the AC's temperature set-point is not determined based on the users' preferences. This latter factor is compounded by the fact that different people may have different choices of temperature set-points and sensitivities to change of temperature. Therefore, it is a challenging task to design an office policy to decide on a particular set-point based on such a diverse preference set. As a result, users are not aware of the energy consumption in shared spaces, which may potentially increase the energy wastage and related cost of office buildings. In this context, this paper proposes an energy policy for an office shared space by exploiting an established temperature control mechanism. In particular, we choose meeting rooms in an office building as the test case and design a policy according to which each user of the room can give a preference on the temperature set-point and is paid for felt discomfort if the set-point is not fixed according to the given preference. On the other hand, users who enjoy the thermal comfort compensate the other users of the room. Thus, the policy enables the users to be cognizant and responsible for the payment on the energy consumption of the office space they are sharing, and at the same time ensures that the users are satisfied either via thermal comfort or through incentives. The policy is also shown to be beneficial for building management. Through experiment based case studies, we show the effectiveness of the proposed policy.Comment: Journal paper accepted in Energy & Buildings (Elsevier

Feed-Forward Neural Network (FFNN) Based Optimization Of Air Handling Units: A State-Of-The-Art Data-Driven Demand-Controlled Ventilation Strategy

Indiana University-Purdue University Indianapolis (IUPUI)Heating, ventilation and air conditioning systems (HVAC) are the single largest consumer of energy in commercial and residential sectors. Minimizing its energy consumption without compromising indoor air quality (IAQ) and thermal comfort would result in environmental and financial benefits. Currently, most buildings still utilize constant air volume (CAV) systems with on/off control to meet the thermal loads. Such systems, without any consideration of occupancy, may ventilate a zone excessively and result in energy waste. Previous studies showed that CO2-based demand-controlled ventilation (DCV) methods are the most widely used strategies to determine the optimal level of supply air volume. However, conventional CO2 mass balanced models do not yield an optimal estimation accuracy. In this study, feed-forward neural network algorithm (FFNN) was proposed to estimate the zone occupancy using CO2 concentrations, observed occupancy data and the zone schedule. The occupancy prediction result was then utilized to optimize supply fan operation of the air handling unit (AHU) associated with the zone. IAQ and thermal comfort standards were also taken into consideration as the active constraints of this optimization. As for the validation, the experiment was carried out in an auditorium located on a university campus. The results revealed that utilizing neural network occupancy estimation model can reduce the daily ventilation energy by 74.2% when compared to the current on/off control