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Completed Research, December 2019

ASHRAE Research Report RP-1745, Evaluation of Climate Reanalysis Data for Use in ASHRAE Applications

"Data Deserts" Affect How Weather Stations Inform Building Design

From eSociety, December 2019

Meteorological reanalysis models provide hourly snapshots of the state of the atmosphere over an extended period of time. In contrast to the operational weather forecast models on which they are based, reanalysis models focus on historical weather. From these snapshots, a continuous weather time series can be assembled for all locations on Earth. For the purposes of ASHRAE, these “virtual” weather stations can be used in the absence of more conventional stations to calculate design climatic conditions or as input to building simulation software. However, these virtual stations may not reflect the reality on the ground, putting building design at risk. 

In a recent ASHRAE research report, Michael Roth, Ph.D., Member ASHRAE, describes ASHRAE-sponsored Research Project 1745 to evaluate the feasibility of the use of reanalyses by its members. 

Roth discusses his research. 

1. What is the significance of this research?

Through chapter 14 in the ASHRAE Handbook—Fundamentals, and Standard 169-2013, Climatic Data for Building Design Standards, ASHRAE provides climatic design information for use by building design professionals for locations throughout the world. However, there are vast regions around the world, so-called "data deserts", where weather data is unavailable, often in undeveloped countries. Reanalysis datasets, provided by agencies such as the National Oceanic and Atmospheric Administration (NOAA), NASA or the European Centre for Medium-Range Weather Forecasts (ECMWF), provide "virtual" weather stations, which can serve to replace the information typically found in a ground-based weather station. These virtual stations span the globe, report every hour without fail and are consistent with all that is known about the dynamics and physics of the earth's climate system—potentially filling in these data deserts.

2. Why is it important to explore this topic now?

Building design professionals are using these reanalysis datasets as a replacement for the more conventional station-based weather data. This usage comes at a risk: is the data accurate? The purpose of 1710-RP, Effect of Dynamic Shading Devices on Daylighting and Energy Performance of Perimeter Zones, was to evaluate the reanalyses against ground stations and provide guidance on its usage.

3. What lessons, facts and/or guidance can an engineer working in the field take away from this research?

While reanalyses do provide information, they do struggle in "problem" locations: near coastlines (land-sea contrast), within cities (urban heat island) or in places where the topography changes rapidly (small islands, mountain peaks and valleys).

Reanalyses also tend to capture average values (e.g. average monthly temperatures) but may poorly represent the more episodic extreme values that are often used in the design of building HVAC equipment.

Finally, reanalyses require specialized expertise and large investments in time, storage and computational power—somewhat limiting its generalized usage.

4. How can this research further the industry's knowledge on this topic?

As part of the research, a software package was developed that allows users to download the data, store it in a database, access it quickly and translate it into a useful format for input to building performance software like EnergyPlus.

5. Were there any surprises or unforeseen challenges for you when preparing this research?

A perhaps surprising result is that it is often better to use a ground-based weather station, even if hundreds of miles away from the desired location, rather than to rely on reanalysis.