Iain S. Walker

Home Energy Article: A Systems Approach to RetrofittingResidential HVAC Systems

LBNL 57406 E RNEST O RLANDO L AWRENCE B ERKELEY N ATIONAL L ABORATORY Home Energy Article: A Systems Approach to Retrofitting Residential HVAC Systems J.A. McWilliams and I.S. Walker Environmental Energy Technologies Division April 2005

A comparison of the power law to quadratic formulations for air infiltration calculations

Although the power law has been broadly accepted in measurement and air infiltration standards, and in many air infiltration calculation methods, the assumption that the power law is true over the range of pressures that a building envelope experiences has not been well documented. In this paper, we examine the validity of the power law through theoretical analysis, laboratory measurements of crack flow and detailed field tests of building envelopes. The results of the theoretical considerations and field and laboratory measurements indicate that the power law is valid for low pressure building envelope leakage.

RESIDENTIAL THERMOSTATS: COMFORT CONTROLS IN CALIFORNIA HOMES

This report summarizes results of a literature review, a workshop, and many meetings with demand response and thermostat researchers and implementers. The information obtained from these resources was used to identify key issues of thermostat performance from both energy savings and peak demand perspectives. A research plan was developed to address these issues and activities have already begun to pursue the research agenda.

Indoor Air Quality in 24 California Residences Designed as High-Performance Homes

Todays high-performance homes are reaching previously unheard of levels of airtightness and are using new materials, technologies, and strategies for which impacts on indoor air quality cannot be fully anticipated from prior studies. This research study used pollutant measurements, home inspections, diagnostic testing, and occupant surveys to assess indoor air quality in a heterogeneous sample of 24 new or deeply retrofitted homes designed to be high-performance homes in California; homes were not all built or certified to the same performance standard (e.g., California Title 24). Although the mechanically vented homes were six times as airtight as non-mechanically ventilated homes (medians of 1.1 and 6.1 ACH50, n = 11 and n = 8, respectively), their use of mechanical ventilation systems and possibly window operation meant their median air exchange rates were almost the same (0.30 versus 0.32 hr—1, n = 8 and n = 8, respectively). Pollutant levels were also similar in vented and unvented homes. Numerous faults were observed in complex mechanical ventilation systems, and they were not corrected as part of this study. More rigorous commissioning is recommended to avoid or correct these faults. Cooking exhaust systems were used inconsistently, and several suffered from design flaws. Failure to follow best practices led to indoor air quality problems in some cases. Ambient nitrogen dioxide benchmarks were exceeded or nearly so in four homes that either used gas ranges with standing pilots or in passive house-style homes that used gas cooking burners without venting range hoods. Homes without active particle filtration had particle count concentrations approximately double those in homes with enhanced filtration, though the effects could not be controlled for outside particle levels and mixing in forced-air homes. The majority of homes reported using low-emitting materials; consistent with this, formaldehyde levels were approximately half those previously measured by another study in conventional, new California homes built before 2008. Emissions of ultrafine particles (with diameters <100 nm) were about 40 times lower on induction electric cooktops compared with either gas or resistance electric models. These results indicate that high-performance homes can achieve acceptable and even enhanced indoor air quality by providing adequate general mechanical ventilation, using low-emitting materials, providing mechanical particle filtration, incorporating well-designed exhaust ventilation for kitchens and bathrooms, educating occupants to use the kitchen and bath ventilation, and possibly by installing induction cooktops.

Potential Benefits of Commissioning California Homes

LBNL-48258 Potential Benefits of Commissioning California Homes Nance Matson, Craig Wray, Iain Walker, Max Sherman Environmental Energy Technologies Division Energy Performance of Buildings Group Indoor Environment Department Lawrence Berkeley National Laboratory Berkeley, CA 94720 January 2002 This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Building Technology, State and Community Programs, Office of Research and Development, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. This report was prepared as a result of work sponsored by the California Energy Commission. It does not necessarily represent the views of the Commission, its employees, or the State of California. The Commission, the State of California, its employees, contractors and subcontractors make no warranty, express or implied, and assume no legal liability for the information in this report, nor does any party represent that the use of this information will not infringe upon privately owned rights. This report has not been approved or disapproved by the Commission nor has the Commission passed upon the accuracy or adequacy of the information in this report.

Uncertainties in Air Exchange using Continuous-Injection, Long-Term Sampling Tracer-Gas Methods

Abstract The PerFluorocarbon Tracer (PFT) method is a low-cost approach commonly used for measuring air exchange in buildings using tracer gases. It is a specific application of the more general Continuous–Injection, Long-Term Sampling (CILTS) method. The technique is widely used but there has been little work on understanding the uncertainties (both precision and bias) associated with its use, particularly given that it is typically deployed by untrained or lightly trained people to minimize experimental costs. In this article we will conduct a first-principles error analysis to estimate the uncertainties and then compare that analysis to CILTS measurements that were over-sampled, through the use of multiple tracers and emitter and sampler distribution patterns, in three houses. We find that the CILTS method can have an overall uncertainty of 10 to 15% in ideal circumstances, but that even in highly controlled field experiments done by trained experimenters expected uncertainties are about 20%. In addition, there are many field conditions (such as open windows) where CILTS is not likely to provide any quantitative data. Even avoiding the worst situations CILTS should be considered as having a factor of two uncertainty for the broad field trials that it is typically used in. We provide guidance on how to deploy CILTS and design the experiment to minimize uncertainties.

Improving air handler efficiency in residential HVAC applications

In continuing the development of energy efficiency standards, consideration has turned to air handlers used for heating and air conditioning of consumer residences. These air handlers have typical efficiencies of about 10% to 15% due to poor electric motor performance and aerodynamically poor fans and fan housings. This study was undertaken to examine some of these performance issues, under carefully controlled laboratory conditions, to support potential regulatory changes. In addition, this study examined the performance of a prototype air handler fan assembly that offers the potential for substantial increases in performance. This prototype and a standard production fan were tested in a full-scale duct system and test chamber at LBNL which was specifically designed for testing heating, ventilation, and air conditioning systems. The laboratory tests compared efficiency, total airflow, sensitivity to duct system flow resistance, and the effects of installation in a smaller cabinet. The test results showed that, averaged over a wide range of operating conditions, the prototype air handler had about twice the efficiency of the standard air handler and was less sensitive to duct system flow resistance changes. The performance of both air handlers was significantly reduced by reducing the space between the air handler and the cabinet it was installed in. Therefore any fan rating needs to be performed using the actual cabinet it will be used in.

Guidelines for residential commissioning

Currently, houses do not perform optimally or even as many codes and forecasts predict, largely because they are field assembled and there is no consistent process to identify problems or to correct them. Residential commissioning is a solution to this problem. This guide is the culmination of a 30-month project that began in September 1999. The ultimate objective of the project is to increase the number of houses that undergo commissioning, which will improve the quality, comfort, and safety of homes for California citizens. The project goal is to lay the groundwork for a residential commissioning industry in California focused on end-use energy and non-energy issues. As such, we intend this guide to be a beginning and not an end. Our intent is that the guide will lead to the programmatic integration of commissioning with other building industry processes, which in turn will provide more value to a single site visit for people such as home energy auditors and raters, home inspectors, and building performance contractors. Project work to support the development of this guide includes: a literature review and annotated bibliography, which facilitates access to 469 documents related to residential commissioning published over the past 20 years (Wray et al. 2000), an analysis of the potential benefits one can realistically expect from commissioning new and existing California houses (Matson et al. 2002), and an assessment of 107 diagnostic tools for evaluating residential commissioning metrics (Wray et al. 2002). In this guide, we describe the issues that non-experts should consider in developing a commissioning program to achieve the benefits we have identified. We do this by providing specific recommendations about: how to structure the commissioning process, which diagnostics to use, and how to use them to commission new and existing houses. Using examples, we also demonstrate the potential benefits of applying the recommended whole-house commissioning approach to such houses.

A simplified model for estimating population-scale energy impacts of building envelope air-tightening and mechanical ventilation retrofits

Changing the air exchange rate of a home affects the annual thermal conditioning energy. Large-scale changes to air exchange rates of the housing stock can significantly alter the residential sectors energy consumption. However, the complexity of existing residential energy models is a barrier to the accurate quantification of the impact of policy changes on a state or national level. The Incremental Ventilation Energy (IVE) model introduced here combines the output of simple air exchange models with a limited set of housing characteristics to estimate the associated change in energy demand of homes. The IVE model was designed specifically to enable modellers to use existing databases of housing characteristics to determine the impact of ventilation policy change on a population scale. The IVE model estimates of energy change when applied to US homes with limited parameterization are shown to be comparable to the estimates of a well-validated, complex residential energy model.

Applying Large Datasets to Developing a Better Understanding of Air Leakage Measurement in Homes

Abstract Air tightness is an important property of building envelopes. It is a key factor in determining infiltration and related wall-performance properties such as indoor air quality, maintainability and moisture balance. Air leakage in U.S. houses consumes roughly 1/3 of the HVAC energy but provides most of the ventilation used to control IAQ. There are several methods for measuring air tightness that may result in different values and sometimes quite different uncertainties. The two main approaches trade off bias and precision errors and thus result in different outcomes for accuracy and repeatability. To interpret results from the two approaches, various questions need to be addressed, such as the need to measure the flow exponent, the need to make both pressurization and depressurization measurements and the role of wind in determining the accuracy and precision of the results. This article uses two large datasets of blower door measurements to reach the following conclusions. For most tests the pressure exponent should be measured but for wind speeds greater than 6 m/s a fixed pressure exponent reduces experimental error. The variability in reported pressure exponents is mostly due to changes in envelope leakage characteristics. It is preferable to test in both pressurization and depressurization modes due to significant differences between the results in these two modes.