Yashen Lin

Ancillary Service to the Grid Through Control of Fans in Commercial Building HVAC Systems

The thermal storage potential in commercial buildings is an enormous resource for providing various ancillary services to the grid. In this paper, we show how fans in Heating, Ventilation, and Air Conditioning (HVAC) systems of commercial buildings alone can provide substantial frequency regulation service, with little change in their indoor environments. A feedforward architecture is proposed to control the fan power consumption to track a regulation signal. The proposed control scheme is then tested through simulations based on a calibrated high fidelity non-linear model of a building. Model parameters are identified from data collected in Pugh Hall, a commercial building located on the University of Florida campus. For the HVAC system under consideration, numerical experiments demonstrate how up to 15% of the rated fan power can be deployed for regulation purpose while having little effect on the building indoor temperature. The regulation signal that can be successfully tracked is constrained in the frequency band [1/τ0,1/τ1], where τ0 ≈ 3 minutes and τ1 ≈ 8 seconds. Our results indicate that fans in existing commercial buildings in the U.S. can provide about 70% of the current national regulation reserve requirements in the aforementioned frequency band. A unique advantage of the proposed control scheme is that assessing the value of the ancillary service provided is trivial, which is in stark contrast to many demand-response programs.

Agent-based and graphical modelling of building occupancy

We propose a novel stochastic agent-based model of occupancy dynamics in a building with an arbitrary number of zones and occupants. Simulation of the model yields time-series of the location of each agent (a software representation of an occupant). The model is meant to provide realistic simulation of occupancy dynamics in non-emergency situations. Comparison of the models prediction of distributions of random variables such as first arrival time of a building is provided against those estimated from measurements in commercial buildings. We also propose a lower complexity graphical model of occupancy evolution in multi-zone buildings. The graphical model captures information on mean occupancy and correlation among occupancy at various zones in the building. The agent-based model can be used in conjunction with building performance simulation tools, while the graphical model is more suitable for real-time applications, such as occupancy estimation with noisy sensor measurements.

Experimental Evaluation of Frequency Regulation From Commercial Building HVAC Systems

Automated demand response can be a valuable resource for ancillary services in the power grid. This paper illustrates this value with the first experimental demonstration of frequency regulation from commercial building heating ventilation and air conditioning (HVAC) systems. The experiments were conducted in Pugh Hall, a 40000 sq. ft. commercial building located at the University of Florida. Detailed are the steps required to make this possible, including control architecture, system identification, and control design. Experiments demonstrate: that satisfactory frequency regulation service can be provided by the HVAC system without noticeable effect on the indoor climate, and the ancillary service provided by this system passes the qualification criteria for participating in the Pennsylvania-New Jersey-Maryland (PJM) interconnections frequency regulation market.

Ancillary service for the grid via control of commercial building HVAC systems

The thermal storage potential in buildings is an enormous untapped resource for providing various services to the power grid. The large thermal capacities of commercial buildings in particular make the power demands of their Heating, Ventilation, and Air Conditioning (HVAC) systems inherently flexible. In this paper, we show how fans in air handing units (AHUs) of commercial buildings alone can provide substantial regulation service, with little change in their indoor environments. A feedforward architecture is proposed to control the fan power consumption to track a regulation signal. The proposed control scheme is then tested through simulations based on a high fidelity commercial building model constructed based on Pugh Hall located on the University of Florida campus. For the HVAC system under consideration, numerical experiments demonstrate how up to 15% of fan power capacity can be deployed for regulation purposes while having little effect on the building inside temperature. The regulation signal can be successfully tracked in the frequency band [1/τ0, 1/τ1], where τ0 ≈ 3 minutes and τ1 ≈ 8 seconds. Our results indicate that fans in existing commercial buildings in the U.S. can provide about 70% of the current national regulation reserve in the aforementioned frequency band.

Low-frequency power-grid ancillary services from commercial building HVAC systems

With the introduction of volatile renewable energy sources into the grid, the need for inexpensive ancillary service increases. We propose a method to provide ancillary service by using the flexibility of demand in commercial building HVAC (Heating, Ventilation, Air-Conditioning) systems. In particular, we show how a regulation command transmitted by a balancing authority can be tracked by varying the cooling demand in commercial buildings in real-time. A key idea here is the bandwidth limitation of the regulation signal, which allows the buildings HVAC system to provide this service with little effect on the indoor climate. The proposed control scheme can be applied on any building with a VAV (Variable Air Volume) system and on-site chiller(s). Simple calculations show that the commercial buildings in the U.S. can provide 47 GW of regulation reserves in the frequency band f ∈ [1=(60 min);1=(3 min)] with virtually no change in the indoor climate, while meeting current ISO/RTO standards for regulation.

Ancillary services to the grid from commercial buildings through demand scheduling and control

How can a building Heating, Ventilation, Air Conditioning (HVAC) system vary its real time power consumption to provide ancillary services to the power grid without sacrificing occupant comfort? Prior work showed how this can be done if the reference power variation is of high frequency (seconds to a few minutes) so that the climate control system filters out the disturbance. This paper addresses the question of how to do that when the reference power variation is of lower frequency, e.g., periods of a few minutes to an hour. We propose a receding horizon approach to schedule the baseline cooling and heating power of a building based on weather forecasts. A lower level controller is then used to track the scheduled baseline plus ancillary service reference signal. Periodic updates to the scheduler based on measurements ensure quality of service in spite of forecasting errors. The algorithm is tested in simulation. Results show that ancillary service in the frequency range of f ∈ [1/(1 hour), 1/(10 minutes)] can be extracted from commercial building HVAC systems while still maintaining a comfortable indoor climate.

An experimental investigation of occupancy-based energy-efficient control of commercial building indoor climate

We present results from a week-long experimental evaluation of a scalable control algorithm for a commercial building heating, ventilation, and air-conditioning (HVAC) system. The experiments showed that the controller resulted in 37% energy savings without sacrificing indoor climate. In contrast to prior work that reports energy savings without a careful measure of the effect on indoor climate, we verify that the controller achieves the energy efficiency improvements without any adverse effect on the indoor climate compared to the buildings baseline controller. This is established from measurements of a host of environmental variables and analysis of before-after occupant survey results. We present a complete system to retrofit existing buildings including the control algorithm and the supporting execution platform which includes the deployment of a wireless sensor network. Results show that there is a large variation in energy savings from zone to zone, which indicates that estimating energy savings potential of novel HVAC control systems is not trivial even from experiments-something that prior work with uniformly positive messages did not emphasize.

Ancillary Services Through Demand Scheduling and Control of Commercial Buildings

Prior work showed building Heating, Ventilation, Air Conditioning (HVAC) systems can provide ancillary services to the power grid without sacrificing occupant comfort if the reference power variation is of high frequency (seconds to a few minutes). This paper addresses the question of how to do that when the reference power variation is of lower frequency, e.g., periods of a few minutes to an hour. The proposed control system to do so uses a two-layer architecture. An optimizer schedules the baseline cooling and heating power of a building based on load forecasts. A lower level controller is then used to track the scheduled baseline plus ancillary service reference signal. The schedule is periodically updated based on indoor measurements to ensure quality of service in spite of load forecasting error. The algorithm is tested in simulation. Results show that ancillary services in the frequency range of f ∈ [1/(1 hour), 1/(10 minutes)] can be extracted from commercial building HVAC systems while still maintaining a comfortable indoor climate.

Demand side frequency regulation from commercial building HVAC systems: An experimental study

Demand side resources can be valuable for providing inexpensive ancillary services to the power grid. This paper present an experimental demonstration of providing frequency regulation from a commercial building Heating Ventilation and Air Conditioning (HVAC) system. The experiments were conducted in Pugh Hall, a 40,000 sq. ft. commercial building located at the University of Florida. In this paper, we describe the steps required to make this possible, including control architecture, system identification, and control design. The field experiments demonstrate: 1. satisfactory frequency regulation service can be provided by the HVAC system without noticeable effect on the indoor climate, and 2. the ancillary services provided by this system passes the qualification criteria for participating in PJM Interconnections frequency regulation market.

Experimental evaluation of occupancy-based energy-efficient climate control of VAV terminal units

Results are presented from a nearly week-long experimental evaluation of a scalable control algorithm for a commercial building HVAC system based on real-time measurements of occupancy obtained from motion detectors. The control algorithm decides air flow rate and amount of reheat for each variable air volume terminal box based on real-time measurements of occupancy and space temperature. It is a rule-based controller, so the control computations are simple. The experiments showed that the proposed controller resulted in 37% energy savings over baseline on average without sacrificing indoor climate. In contrast to prior work that reports energy savings without a careful measure of the effect on indoor climate, it is verified that the controller indeed maintains indoor climate as well as the buildings baseline controller does. This verification is performed from measurements of a host of environmental variables and analysis of before/after occupant survey results. A complete system required to retrofit existing buildings with the controller is presented, which includes a wireless sensor network and a software execution platform. Two useful observations from this work are: (i) considerable energy savings—along with compliance with ASHRAE ventilation standards—are possible with simple occupancy-based control algorithms that are easy to retrofit; and (ii) these savings are attained with binary occupancy measurements from motion detectors that do not provide occupancy-count measurements. Results also show that there is a large variation in energy savings from zone to zone and from day to day.