Craig Christensen

Solar Advisor Model User Guide for Version 2.0

The Solar Advisor Model (SAM) provides a consistent framework for analyzing and comparing power system costs and performance across the range of solar technologies and markets, from photovoltaic systems for residential and commercial markets to concentrating solar power and large photovoltaic systems for utility markets. This manual describes Version 2.0 of the software, which can model photovoltaic and concentrating solar power technologies for electric applications for several markets. The current version of the Solar Advisor Model does not model solar heating and lighting technologies.

Method for Determining Optimal Residential Energy Efficiency Retrofit Packages

Businesses, government agencies, consumers, policy makers, and utilities currently have limited access to occupant-, building-, and location-specific recommendations for optimal energy retrofit packages, as defined by estimated costs and energy savings. This report describes an analysis method for determining optimal residential energy efficiency retrofit packages and, as an illustrative example, applies the analysis method to a 1960s-era home in eight U.S. cities covering a range of International Energy Conservation Code (IECC) climate regions. The method uses an optimization scheme that considers average energy use (determined from building energy simulations) and equivalent annual cost to recommend optimal retrofit packages specific to the building, occupants, and location. Energy savings and incremental costs are calculated relative to a minimum upgrade reference scenario, which accounts for efficiency upgrades that would occur in the absence of a retrofit because of equipment wear-out and replacement with current minimum standards.

Verification and Validation of EnergyPlus Conduction Finite Difference and Phase Change Material Models for Opaque Wall Assemblies

Phase change materials (PCMs) represent a potential technology to reduce peak loads and HVAC energy consumption in buildings. There are few building energy simulation programs that have the capability to simulate PCM but their accuracy has not been completely tested. This report summarizes NREL efforts to develop diagnostic tests cases to obtain accurate energy simulations when PCMs are modeled in residential buildings.

Analysis of System Strategies Targeting Near- Term Building America Energy-Performance Goals for New Single-Family Homes FY 2004 Fourth-Quarter Building America Milestone Report

The Building America residential systems research project uses an analysis-based system research approach to (1) Identify research priorities, (2) Identify technology gaps and opportunities, (3) Establish a consistent basis to track research progress, (4) Increase the cost effectiveness of research investments by identifying system solutions that are most likely to succeed as the initial targets for residential system research projects. This report describes the technical approach used by Building America to determine the most cost effective pathways to achieve whole-house energy savings goals. The report provides an overview of design/technology strategies leading to net zero energy buildings as the basis for analysis of future residential system performance. The analysis approach is demonstrated by providing an initial comparison of the least-cost options required to achieve 40% energy savings in five climate zones. The preliminary results from this study will be validated against field studies and updated on an annual basis to reflect best available residential system cost/performance data from ongoing Building America research activities.

Identifying and Resolving Issues in EnergyPlus and DOE-2 Window Heat Transfer Calculations

Issues in building energy software accuracy are often identified by comparative, analytical, and empirical testing as delineated in the BESTEST methodology. As described in this report, window-related discrepancies in heating energy predictions were identified through comparative testing of EnergyPlus and DOE-2. Multiple causes for discrepancies were identified, and software fixes are recommended to better align the models with the intended algorithms and underlying test data.

An Optimization Methodology for Zero Net Energy Buildings

A zero net energy building (ZNEB) is grid-tied, net metered and produces as much energy on-site as it uses in a typical year. In this paper, we describe methods to cost optimize designs for ZNEB’s. The goal is to find a constrained optimum, i.e., the minimum-cost design that achieves ZNE. Increased first costs for improved efficiency are balanced against the size of the PV system required to achieve ZNE (where the net-metered PV system is the energy source of last resort, because it is expensive but can meet the remaining load “using the grid for storage”). Discrete building component options are considered within various categories (e.g., walls, ceilings, foundations, glass types, air conditioners, furnaces, etc.). Each category is optimized by balancing the marginal cost of saved energy for efficiency options against the cost of energy from the PV system. Categories are optimized sequentially with iteration to adjust for possible interactions between categories. The process is automated with software that manipulates input files, launches DOE2 simulations, reads the results, and executes the optimization methodology.Copyright

Cost and Performance Solar Analysis Model for All Solar Technologies

A comprehensive solar technology systems analysis model is being developed at NREL to support program planning for the U.S. Department of Energy’s Solar Energy Technologies Program (SETP). This new model will calculate the costs, finances and performance of current solar technologies including solar heat (typically solar domestic hot water), concentrating solar power, photovoltaics (PV) and solar hybrid lighting. The primary function of the model is to allow users to investigate the impact of variations in physical, cost, and financial parameters to better understand their impact on key figures of merit. Although a variety of models already exist to examine various issues with each individual technology, this model, when fully implemented in the future, will have the capability to analyze and compare different solar technologies (utility-scale PV vs. CSP for example) within the same interface while making use of similar cost and financing assumptions. A central idea for this model is to have a user-friendly interface while at the same time having a detailed, accurate analysis for each of the technologies. The underlying performance engine, which is hidden from the user, is TRNSYS, which already contains an extensive library of solar technology models. There are built-in cost models or the user can access their own spreadsheet-based cost model. The financial model is an extension of an existing validated finance model. This paper will discuss the goals and implementation of the model and present several sample results for interesting sensitivities.Copyright

USING THE BEOPT AUTOMATED RESIDENTIAL SIMULATION TEST SUITE TO ENABLE COMPARATIVE ANALYSIS BETWEEN ENERGY SIMULATION ENGINES

Verification and validation are crucial software quality control procedures to follow when developing and implementing models. This is particularly important because a variety of stakeholders rely on accurate predictions from building simulation programs. This study uses the BEopt Automated Residential Simulation Test Suite (BARTS) to facilitate comparison of two energy simulation engines across various building components and includes building models that isolate the impacts of specific components on annual energy consumption. As a case study, BARTS has been used to identify important discrepancies between the engines for several components of the building models. These discrepancies are caused by differences in the algorithms used by the engines or coding errors.

Time-of-Use Monitoring of U.S. Coast Guard Residential Water Heaters With and Without Solar Water Heating in Honolulu, HI

A combination of high energy costs, uniform solar resource, and an active solar industry combine to make Hawaii a good location for cost effective applications of solar water heating. The non-freezing climate allows for simple solar water heating system designs. In the mild climate of Hawaii, solar water heating can displace a large fraction of a home’s electricity use since heating and cooling loads are small. In 1998, sixty-two solar water heaters were installed at Kiai Kai Hale US Coast Guard Housing Area in Honolulu, HI as a pilot project under a grant from the US DOE Federal Energy Management Program (FEMP). The systems are active, open loop systems with a single tank (electric water heater with the bottom element disabled). An assessment of these pilot units will help inform a Coast Guard decision regarding implementing solar water heating on the remaining 256 units in the housing area, and may be useful information for other government and utility programs. On 25 houses with solar water heating and 25 identical houses without solar, instruments were installed to measure on/off cycles of the electric water heaters and the tank outlet temperature. This paper describes the results the monitoring for a six week period From June 11 to July 25, 2002, with a statistical extrapolation to estimate annual savings. Demand savings are estimated at 1.62 kW/house, energy savings at 3,008 kWh/house/year, and annual cost savings per house is estimated at

Heat Pump Water Heating Modeling in EnergyPlus

380/year due to solar. For a system cost of