Indoor climate control in multi-unit grid-interactive efficient buildings
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Authors
Naqvi, Syed Ahsan Raza
Issue Date
2022-12
Type
Electronic thesis
Thesis
Thesis
Language
en_US
Keywords
Electrical engineering
Alternative Title
Abstract
In this work, we develop a number of energy management policies for building heating,ventilation and cooling (HVAC) systems for satisfying various objectives. Control policies
whose objective is to improve building operations are primarily aimed at economizing indoor
climate control operations. On the other hand, occupant-centric control strategies prioritize
the comfort of individual occupants. In this dissertation, we evaluate the performance of
some of these policies in both simulated and physical setups.
The thermal inertia of buildings, along with the flexibility associated with thermostatically controlled loads (TCLs) allows HVAC systems to be used for grid demand response
(DR). The initial few chapters of this report develop control strategies aimed at minimizing
the operational costs of a building’s HVAC system. We first consider a hydronic HVAC
system that serves multiple units in a residential building to meet their space heating requirements. We determine the optimal power flow to each unit that minimizes the energy
costs (EC) incurred by the building while keeping in consideration the occupants’ thermal
comfort. The building is assumed to participate in a DR program which allows the building
temperatures to deviate from the set-points up to a maximum limit. Despite the complex, non-linear structure of the problem, we show how the optimal solutions can be obtained
efficiently using quadratic programming. Since HVAC systems can run on either electricity
or natural gas, we study the efficacy of the DR regime for both hourly electricity prices and
flat gas prices over the course of 24 hours. We also study the optimal thermal power and
the evolution of unit temperatures for various energy pricing schemes.
Subsequently, we expand the scope of our work to include TCLs in large commercial
buildings. The load profiles of most commercial and industrial consumers are characterized
by brief periods of very high power consumption followed by intervals of lower demand.
To encourage such consumers to flatten their load profiles, power utilities in around the
world often levy a monthly demand charge (DC) on the peak demand measured over brief
intervals. It was seen in the preceding study that a control policy that minimizes EC while
being agnostic to instantaneous power consumption can introduce significant spikes in the
building’s demand patterns. Therefore, we expand our study on hydronic HVAC systems
to consider the joint optimization of EC and the instantaneous peak power of a multi-unit
building that participates in a DR program. We study the power demand patterns resulting
from our proposed control strategy for TCLs, and evaluate its performance for various climate
zones in the US, under both typical and atypical weather conditions. The results show that
depending on the ambient conditions and the tariff structure, our control policy can result
in utility bill savings of up to nearly 19% compared to the baseline. Our power control
strategy was also seen to significantly reduce the instantaneous peak power consumption in
commercial TCLs.
The work summarized hitherto is primarily centered around developing theoretical
control frameworks for building HVAC systems as desired by building operators (BOs).
However, the next part of the research presented in this report develops multiple control
strategies for heating and cooling operations in buildings for meeting the objectives of both
the BO and the building occupants. Moreover, this part of our report develops a prototype
for autonomous temperature management schemes that can be readily deployed in a real-life
shared workspace. Specifically, we study the problem of indoor zone temperature control in
shared workspaces equipped with heterogeneous heating and cooling sources with the goal
of increased energy savings and environment personalization. Shared workspaces typically
witness distinct intervals when they are occupied or are unoccupied. Moreover, these intervals generally follow a fixed schedule which may be known in advance. In this work, we develop control strategies for space heating and cooling operations to achieve the various indoor conditioning objectives for each of these distinct intervals. Specifically, we consider two
contiguous intervals of equal duration where a shared workspace remains unoccupied prior to
hosting a scheduled event, such as a work meeting. For the first interval, when the workspace
is unoccupied, we propose multiple time-bound pre-cooling/pre-heating control strategies for
conditioning the workspace in preparation for a scheduled activity (Phase I). For the second interval, when the workspace is occupied, we propose a separate control strategy which
enhances the thermal comfort of the occupants by harnessing the spatial differentiation of
the thermal environment to satisfy the different temperature preferences of the individuals
(Phase II). Utilizing a physical test-bed, we use data-driven model learning to establish a
relationship between the HVAC control inputs of the indoor space, and the zone temperatures. Next, we present a simple control strategy to achieve the pre-conditioning objective in
Phase I and show that it is less computationally expensive than conventional model predictive control (MPC). For Phase II, we then use a simple, low complexity, quadratic program
to minimize the thermal discomfort experienced by individuals based on their temperature
preferences. The experimental results show that for Phase I, the proposed control policies
can save a significant amount of energy and achieve the desired mean temperature in the
space fairly accurately. We further note that for Phase II, the control scheme can achieve a
significant spatial differentiation in temperature towards satisfying the occupants’ thermal
preferences.
Occupant well-being requires not only efficient indoor thermal management but also
indoor air quality (IAQ) management. Control strategies aimed at improving the efficiency
of HVAC systems while enhancing occupant wellness must jointly optimize ventilation as
well as heating and cooling operations. The final direction of this work studies the problem
of minimizing the energy consumption of the HVAC system in a multi-unit building, while
meeting thermal comfort and IAQ requirements. Here, we use zonal carbon dioxide (CO2)
to be an indicator for IAQ in individual zones. We first perform a steady state analysis of
the zonal CO2 concentration and the temperature dynamics. The resulting expressions are
convex in the zonal mass flow rates and zonal temperatures. Guided by the steady state
solutions for meeting the thermal comfort constraints, we develop two control policies for
improving the energy efficiency of building HVAC systems while jointly satisfying indoor
temperature and IAQ constraints. We compare the performance of our proposed approaches with those of multiple baseline approaches which implement separate regimes for managing
zonal temperature and IAQ for a typical work-day in a multi-zone campus building. We have
evaluated the performance of our proposed approaches under varying levels of flexibility in
zonal temperatures. Our proposed approaches were seen to offer potential savings of nearly
29% compared to the baseline.
In the closing chapter of this report, we offer some remarks pertaining to the results
obtained from the aforementioned studies. We conclude this report by proposing possible
extensions to this work.
Description
December2022
School of Engineering
School of Engineering
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY