On-Site Combined Cooling & Power For Data Centers
August 1, 2011
Regulatory, competitive, and environmental pressures are pushing data centers away from the traditional power sources. Here, the author surveys the landscape and reviews one comparative study involving CCP cogeneration and conventional electricity sources. Reducing the carbon footprint and lessening reliance on a sometimes unreliable grid are just two reasons to look into CCP.
Our nation’s existing and currently planned remote coal- and gas-fired electric power generating stations (EPGS) are unsustainable in terms of greenhouse gas (GHG) emissions, expressed in pounds CO2kWh, their associated thermal pollution, and serious consequential global climatic effects estimated by scientific and engineering experts as reported in the executive summary of the U.S. Global Change Research Program report titled, “Global Change Impacts in the United States.”
The above-referenced report summary synthesizes information from a wide variety of scientific assessments and recently published research about the observed and projected consequences of foreseeable climatic changes, namely, “Climate-related changes have already been observed globally and in the United States. These include increases in air and water temperatures, reduced frost days, increased frequency and intensity of heavy downpours, a rise in sea level, and reduced snow cover, glaciers, permafrost, and sea ice.”
Furthermore, a collection of market forces driving a new IT business model comprising both remote private and public cloud computer subscription services “is expected to reach $102.1 billion in 2012 up from $68.3 million in 2010,” according to research firm Gartner. The greening of data centers is likely to continue driving infrastructure construction and additional upgrades resulting from advances in virtualization software and blade servers. Trends suggest that new data centers will need to accommodate 200 W/sq ft and replace existing data centers formerly designed on the basis of 50 W/sq ft.
Data center costs can be expected to increase this year 4% to 6% above last year due to more stringent EPA generator regulation, increased sustainable design pressure, and material and labor costs. Tier 3 data center construction costs can be expected to range because cooling costs tend to favor states and localities with colder temperatures (favoring greater free cooling), a perceived lower propensity for bad weather or earthquakes, and a more reliable utility infrastructure. The data center balancing act requires designers to become greener within tight budgetary constraints and power usage metrics.
Server consolidation and virtualization is the principal strategy being currently used to address increasing resource demands to overcome energy wasteful (older) legacy IT equipment by delaying as long as possible the purchase of more efficient, high capital cost newer power and cooling systems. What is needed is a break from the more traditional design-bid-construct process, instead employing a more affordable design-build process focusing on factory prefabricated, modular, and more efficient power and cooling systems. This also can substantially shorten the time needed for construction and allow the data center to come online sooner to receive more immediate customer cash flow.
CARBON-NEUTRAL IMPACTSLet us next try to define “carbon neutral” in terms of today’s realities. Currently, most forms of carbon-neutral energy involve burning at least some fossil fuels. Even crops used to synthesize ethanol and other biofuels cannot be practically harvested without using farm machinery that consumes fossil fuel. Renewable energy sources such as solar cells, wind, and hydroelectric turbines, are all produced and transported using fossil fuels to some extent. Although technology currently exists to make some of these operations truly carbon-neutral, it is clearly economically unviable at this time and unlikely any time in the near term future. Nuclear power production also involves fossil fuels in the mining and transport of uranium, the building of EPGSs, and the disposal of nuclear waste.
Furthermore, as uranium sources are likely to become scarce, mining it is more likely to consume even more fossil fuel than it does presently, as will the need to provide for long-term safe storage of non-recyclable nuclear waste product, etc.
Therefore, for purposes of comparisons involving production of electricity either by on-site combined cooling and power (CCP) cogeneration, gas- or coal-fired EPGS, MSW incineration, and more recently, proposed MSW plasma illustrated in Figure 1, we have chosen to define carbon neutral in relative terms of requiring the least amount of fossil fuel or CO2 produced per kWh delivered to the point of use.
Accordingly, the use of available waste heat becomes the prime energy source in driving building HVAC systems, in lieu of fossil fuels, when designing data centers’ MEP systems.
ECONOMIC ANALYSISTo illustrate the challenge of expected growth in this sector, consider the results of a recent data center client study requiring 3.5 MW for foreseeable peak electrical facility demand along with a peak facility cooling requirement of 2,240 tons. Electricity can either be supplied from an on-site CCP plant or purchased from a remote EPGS. The subject data center power demand established after virtualization then established our benchmark requirements for the CCP requirement is illustrated in Figure 2.
By developing the life-cycle cost analysis (LCC) of our proposed CCP alternative to purchase power from a remote EPSG, one can determine the comparative advantage of budgetary capital equipment costs that were determined including labor and material costs for major CCP equipment during installation; estimated annual energy use cost for CCP plant; and the estimated annual O&M cost for the proposed CCP plant. The LCC analysis assumed a discount rate of 6%, and an O&M escalation rate of 3%.
Our CCP LCC comparison assumed a 20-yr lifetime. Accordingly, the economic analysis results for the proposed data center CCP are illustrated in Figure 3, which includes the CTG waste heat-fired integral HRSG component of the 1,740 RT, two-stage LiBr absorption chiller identified in Figure 2. The LLC as outlined above was also determined to be $105 million.
DATA CENTER STUDY RESULTSIn terms of direct LCC, the economic impact of the CCP option was found to be approximately 34% lower than the remote EPGS purchased power alternative.
Furthermore, including the difference in generating efficiencies through available energy accounting, the CCP alternative was found to be about 20% more effective than the EPGS option, and the projected emissions rate was also favorable for the on-site CCP option after an environmental impact analysis for GHG and NOx was completed.
The two-stage absorption chiller illustrated in Figure 2 was able to produce 1,740 tons employing CTG waste heat, and a 500-ton electric centrifugal chiller was required to meet the above-referenced data center design day 2,240-ton cooling load.
The above-referenced life-cycle economic cost model for the data center CCP was determined, along with beneficial carbon neutral results as illustrated in Table 2, using comparative eco-footprint and CO2 emissions. In addition, the comparative NOx were also compared since EPA recently announced that it is currently planning to issue mandatory NOx curtailment guidelines in the foreseeable future.
Accordingly, we reported to our client that the CCP option was preferable. It is our understanding that the subject data center is awaiting the approval of outside funding. Should the cost of natural gas and electricity continue to rise, we also reported to our client that the time required to amortize the additional CCP capital investment can be expected to drop.
The comparison was also found to be more favorable for CCP should the risk of fuel prices increase significantly as a result of a proposed carbon tax or other regulatory and/or market-driven factors related to climate change legislation now under review by Congress.
A key outcome of the above-referenced data center study is that we were able to establish the fiscal incentive for a CCP power plant, which still requires finalizing CCP equipment selections, CCP plant operational parameters, and preparation of design-build engineering plans and specifications to proceed after client funding and the proposed site selection options have been finalized.
ECO-FOOTPRINTSUsing data from the EPA’s eGRID2006, which provides power plant emissions data for the year 2004, Table 2 assesses the eco-footprints of the CGT-powered CCP equipment illustrated in Figure 1, relative to corresponding EPGS alternative. In terms of GHG emissions, the CHP-based systems can lower emissions by as much as 20%. Since generation technologies, fuel types, and age of plants varies widely between regions, the calculations include a comparison using data from the Western U.S., Northeastern U.S., and the national average. While the magnitude of the results varies somewhat, the overall trend remains the same: emissions from CHP seem to be lower than emissions from EPGS, ranging from 8% to 14% for GHG (Table 2) and ranging from 20% to 37% for NOx (Table 3).
CHANGING DATA CENTER DESIGN TRENDSA number of major U.S. companies - such as HP, I/o Data Centers, LLC, and Dell for example - now offer what they claim is a faster and more cost-efficient modular approach to constructing large data centers, which may result in a claimed 10% to 30% lower first cost due to their assembly-line, prefabricated approach.
Presently, custom-designed data centers comprise acre-sized warehouses filled with computers, virtualized servers, and telecommunication equipment, etc. They often require up to two years to build and can cost in excess of $100 million.
In 2010, for example, HP shifted to the modular approach when it started to sell prefabricated data centers to its customers. Last December, eBay announced that it planned to build a large modular data center in Phoenix. This past April, Dell announced plans to build ten new data centers at various locations around the world also using modules.
In response to a perceived demand for lower first cost and a more timely completion, HP’s director of worldwide critical facilities services anticipated that by 2013, “50% of all new data centers will be built modularly, rather than custom designs … .” Johnson Controls (JCI) currently supplies modular, prefabricated air conditioning systems, and it is anticipating that modular, prefabricated CCP systems will soon be added to this mix to reduce the cost of purchased electricity, a big ticket item for data center users as shown in Figure 4.
Refer to Figure 4 for a alternative modular, prefabricated ICHP, power cooling, thermal energy storage (TES) package DBS designed to serve another client data center to be located within an existing office building, eliminating an exterior container required for the standalone modular,prefabricated CCP power cooling package illustrated in Figure 2. Rather than using the CGT exhaust for a CGT exhaust fired CCP absorption chiller, a heat exchanger is provided to transfer CGT exhaust waste heat to a low-pressure closed circuit high temperature heat transfer(HTHT) loop to drive an indirect fired absorption chiller for data center cooling needs together with a downstream low temperature fired DEMTEC absorption chiller to enable operation of an ice-generated thermal energy system (TES) to reduce current peak cooling demand for other conditioned occupied building areas as well.
Furthermore, market forces driving a new IT business model comprising both remote private and public cloud computer subscription services “is expected to reach $102.1 billion in 2012, up from $68.3 million in 2010,” according to research firm Gartner.
Another concern results from the passage of lead-free regulations, which have caused concerns regarding printed circuitboards, surface-mounted components, hard disk drives, computer work stations, servers, and other devices to the effects of corrosive airborne gaseous and particulate contaminants. In addition, data centers in unban areas are reporting failure of servers and hard drives, resulting in increased warranty costs and potential loss of confidence by customers. Recent efforts by ASHRAE TC 9.9 to relax (i.e., update) data center environmental guidelines to allow HVAC system operations, “in the most energy-efficient manner, involving greater use of outdoor air economizers, to improve its PUE,” may prove counterproductive.
Finally, with respect to greater efforts needed to have data centers approach net zero energy use, that seems highly unlikely without integration with CCP as recommended above for data center airside or liquid cooling.
CONCLUSIONSRegulatory and competitive pressures are increasingly driving a transition away from hydrocarbon fuels towards renewable energy alternatives.
The small fraction of these energy technologies in our existing portfolio - wind, solar, biomass, and geothermal - taken together produced only approximately 3.1% of consumed electricity in the U.S. during the 12-month period ending November 2008. That does not appear promising for the foreseeable future.
There is also strong evidence that the Arctic has experienced dramatic environmental changes over the last 30 years, resulting in a rapid decline in the thickness and extent of sea-ice in summer and recently winter as well. Should the present trends continue, the Arctic could experience ice-free summers within 30 years3 along with a consequential rise in sea levels along our coastal areas.
In terms of pressing environmental concerns, U.S. District Judge Bill Wilson issued an injunction in late October 2010 to halt construction of a $1.7 billion coal-fired power plant in southwest Arkansas, finding that plaintiff conservationist groups had shown, “a likelihood of irreparable harm to the environment.” Expect more resistance to excessive GHG emissions to follow.
The North American Electric Reliability Corp., an industry group charged with ensuring grid reliability of coal-, oil-, and gas-fired power plants with a collective capacity of about 76,000 MW (one MW provides enough power for about 750 homes), recently reported, “Four federal environmental regulations recently issued to improve water and air quality could by 2018 chop by nearly half the amount of projected reserve energy available to the U.S. power if the forthcoming rules are implemented under the fastest proposed timeline.” Under this scenario, “the amount of generating capacity that needs to be on standby to meet peak electricity load in the summer months and to cover for any unexpected generating outages could drop by almost half.”
Most existing and currently planned remote EPGS serving the growing number of data centers must begin to consider the potential impact of the above referenced new EPA rulings and the negative carbon impacts associated with distributing electricity from their remote electric utility generators to the data center customer electric meter. Consequently, the opportunity to incorporate use of CCP cogeneration to mitigate risks associated with above referenced EPGS/grid power availability should be more actively considered for the reasons and beneficial results given earlier. ES
CITED WORKS1. Dollard, J. “Hot Fix for Renewable Energy.” Pollution Engineering. September, 2010.
2. Meckler, M., L. Hyman, et al. “Comparing the Eco-Footprint of On-Site CHP vs. EPGS Systems.” Proceedings ASME 2nd International Conference on Energy Sustainability. 2008.
3. McKay, J.L. et al. “Holocene Fluctuations in Arctic Sea-Ice Cover.” Can. J. Earth Science. 2008:45:1377-1397.