Ashrae Refrigerant Numbers

Using chiller plants in humid zones

Mechanical engineers have always been faced with balancing functionality, health/safety codes, reliability, maintainability, and flexibility. Now the race to achieve net-zero facilities results in a variety of energy and sustainable scenarios that change based on each owner’s individual goals and preferences.

This article will review the use of dual chiller plants to achieve energy efficiency for federal office buildings located in humid climates, specifically in Washington, D.C. While humidity is a relative term, the fact remains that this area of the country enjoys four full seasons of varying weather conditions, along with fairly balanced energy price structures. These conditions can extend the payback of renewable energy investments such as wind or solar to well over 25 years. There are few silver bullets available to achieve enhanced energy goals. Thus, an integrated design approach by the team is necessary.

The facility under discussion represents approximately 360,000 gross sq ft of podium (including entries, a breakfast/lunch kitchen, conference facilities, and fitness center); approximately 1.4 million gross sq ft of tenant-specific office space throughout 15- and 17-story towers connected through the 10th floor; and approximately 1.3 million gross sq ft of parking structures.

Energy efficiency for the project began during the proposal phase in 2008. The building request for proposal (RFP) indicated that ASHRAE 90.1, LEED Silver, and the Energy Policy Act of 2005 were part of the contract requirements. The team reviewed energy model results that incorporated various options for exceeding baseline energy performance for the facility. As a strategy the design-build team chose a combination that not only met the facility’s needs but, more importantly, provided the future ability to exceed the minimum energy goals. This decision resulted in a cost-effective upgrade to LEED Gold for the owner during the construction phase of the project.

Southland Industries, as the mechanical engineer of record, developed initial energy models based on a variety of similar RFP criteria. The modeling showed a progression of energy savings with each added feature. For instance, multiple wall R-values were modeled to investigate the point of diminishing return. This was compared to an R-value of virtual infinity, as a super wall. The process continued adding features based on the anticipated level of impact such as windows, roof, and lighting. After minimizing the loads on the facility, multiple central plant options were explored. Typically any option with less than 1% savings or an extended payback of over 20 years was not necessary to meet the energy goals for this project. This process showed that series counter flow chillers (although successful on a previous project) were not beneficial for this facility. We also knew that decoupling the outdoor air for dehumidification and internal loads was a plus, and found that two separate chiller plants maximized savings, creating a 55 F sensible plant and 42 F standard chiller plant.

Dell makes hotter servers for warmer ASHRAE buildings - by Peter ...

Some servers to be used at 45 Celsius (113 F) for a few hours at a time, instead of the previous limit of 35 Celsius (95 F), without breaking the warranty conditions. It’s given this the name “Fresh Air” but it’s not new technology - just a new warranty.

Dell has refined its warranty to allow servers to have “excursions” in temperature, so they can go at 45 Celsius for up to 90 hours per year, and at 40 Celsius for up to 900 hours. The company has published a explaining how this works.

The new warranty covers the PowerEdge R610, R710 and T610 servers along with some PowerConnect switches, PowerVault storage arrays and EqualLogic products - and the new warranty is available on servers bought up to six months ago.

Dell says this gives it the hottest server warranty on the planet, but it won’t be alone for long. The move is definitely in line with data center trends - as you can see in the activity around ASHRAE.

ASHRAE (the American Society of Heating, Refrigeration and Air-conditioning Engineers) publishes Thermal Guidelines for Data Processing Environments, more usually known as TC 9.9 after the technical committee that produces it, and widely used in planning and designing data centers.

A new (third) edition of TC 9.9 is coming in September, and it’s a big change. This organisation has with the words air-conditioning and refrigeration in its name - and it’s publishing regulations designed to allow data centers to operate without chilling, using free air cooling.

ASHRAE reckons that data centers can be run in May which explains the coming changes.

In order to accommodate free air cooling, ASHRAE has added detail, expanding the number of classes of data center to take into account different purposes, and different levels of control of the environment.

Specifically, it adds two classes, with allowed temperature ranges up to 40 Celsius and 45 Celsius - so it is clearly no coincidence that Dell chose those temperatures for its own extended warranties.

This does over-simplify the ASHRAE work, which also covers the important issue of humidity. However, it is very clear that manufacturers and industry groups are getting together on the idea of running data centers hotter.

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