{"id":9192,"date":"2017-09-08T11:00:19","date_gmt":"2017-09-08T19:00:19","guid":{"rendered":"http:\/\/www.palada.net\/index.php\/2017\/09\/08\/news-2965\/"},"modified":"2017-09-08T11:00:19","modified_gmt":"2017-09-08T19:00:19","slug":"news-2965","status":"publish","type":"post","link":"http:\/\/www.palada.net\/index.php\/2017\/09\/08\/news-2965\/","title":{"rendered":"Why don’t we know how much airflow IT equipment requires?"},"content":{"rendered":"

Credit to Author: Victor Avelar| Date: Fri, 08 Sep 2017 18:00:26 +0000<\/strong><\/p>\n

If you\u2019ve ever tried to find how much airflow a new server requires, then you\u2019ve experienced the frustration of burning precious time to no avail.\u00a0 Finding server airflow requirements should be as easy as finding its power requirements since they are just as important, yet IT equipment vendors leave us guessing on how to properly specify cooling.\"Uniflair<\/p>\n

The air conditioning fans cooling your IT equipment represent roughly 10% of your data center\u2019s entire electric bill (including IT energy), or about 40% of your total cooling energy.[1]<\/a>\u00a0 This energy could be much lower if we didn\u2019t oversize our computer room cooling unit airflow.\u00a0 Certainly, some oversizing occurs due to redundancy, but the oversizing I\u2019m talking about happens because designers don\u2019t know the IT equipment airflow or deltaT.\u00a0 Let me explain.<\/p>\n

The following formula <\/a>quantifies how much heat a server produces OR how much heat a cooling unit rejects.<\/p>\n

\"Airflow <\/p>\n

Q<\/strong>, measured in kilowatts (kW), is the rate of heat produced by the server or heat rejected by the cooling unit.
Airflow<\/strong>, measured in cubic feet per minute (CFM), is the volume of air moving through the server or cooling unit .\u00a0 Data center cooling units typically have a fixed airflow (some are fixed at 100% and some set airflow as a % of maximum).
deltaT<\/strong>, measured in Fahrenheit, is the temperature difference between the server\u2019s exhaust and inlet air or the cooling unit\u2019s return and supply air.\u00a0 Server designers design to a specific deltaT across the server.
(specific heat of air) and \u00a0(density of air) are constants for air at set conditions so these are known.<\/p>\n

When I enter values for the constants along with a conversion to 60 seconds \/ minute (1.08<\/a>), and conversion factor to kW (3,412) I get a more practical formula:<\/p>\n

\"Airflow <\/p>\n

 <\/p>\n

From this formula, you can see that for a given \u201cQ\u201d<\/strong> there are an infinite number of combinations of airflow and deltaT values.\u00a0 For example, an increase in airflow through a cooling unit, results in a decrease in deltaT across the cooling coil and vice-versa.\u00a0 What this means is that when designers size a cooling unit for a given IT \u201cQ\u201d, it WILL<\/strong> remove the IT heat but not at the same airflow and deltaT of the IT equipment.\u00a0 What happens when the cooling unit airflow doesn\u2019t match the IT airflow?\u00a0 Let\u2019s pretend that you are responsible for buying the cooling units to cool a 1,000 kW data center (i.e. 1,000 kW of IT load)[2]<\/a>, but you don\u2019t know the total airflow required by the IT equipment.<\/p>\n

Here are some possible airflow scenarios[3]<\/a> you can choose from, to cool this hypothetical data center, assuming no redundancy or safety factors.\u00a0 In each scenario, there are enough cooling units to cool 1,000 kW of IT load.\u00a0 Which do you choose?\u00a0 If I told you that the total IT airflow requirement was 130,000 CFM or deltaT was 24F, you would choose Scenario D.\u00a0 But you don\u2019t know.\u00a0 So, what happens if you choose Scenario A?\u00a0 In this case, the IT equipment will be starved of cool air and will ingest its own hot exhaust air causing significant hotspots.\u00a0 What happens if you choose Scenario G?\u00a0\u00a0 In this case, the IT equipment will use only the cool air it needs, and the remaining cool air will bypass the IT equipment and return back to the cooling unit without performing any thermodynamic work.\u00a0 Ideally, no hot spots in this scenario but you use 69% more energy than scenario D.<\/p>\n

\"Possible <\/p>\n

 <\/p>\n

Here in lies the dilemma for data center designers.\u00a0 Without knowing the IT airflow requirement or deltaT, it\u2019s understandable why over-specifying airflow occurs.\u00a0 But this means that I\u2019m spending more capital for cooling units, and paying indefinitely for fan energy I don\u2019t need.\u00a0 What this industry needs are for IT equipment vendors to provide the typical and worst-case airflow or deltaT requirements on their spec sheets.\u00a0 I realize that IT equipment fans increase or decrease airflow upon different events like high temperature or high CPU utilization.\u00a0\u00a0 However, this is no reason for IT manufactures to forego publishing the typical and worst-case airflow requirements, so that cooling specifiers don\u2019t oversize your budget and energy bill.<\/p>\n

I would appreciate any comments on your experiences with sizing cooling units for airflow requirements. If you are a designer, how do you manage this issue today?<\/p>\n

__________________________________<\/p>\n

[1]<\/a> Based on a 50% loaded data center, 2N power system, 1N cooling, using chilled water with packaged chiller, no economizer, and room cooling units.<\/h6>\n
[2]<\/a>
Normally you would need to cool non-IT loads as well but, for the purpose of education, let\u2019s assume there is only IT load.<\/h6>\n
[3]<\/a>
Data from Uniflair LE CW Technical Specifications<\/a> assuming 100% sensible cooling (i.e. cooling without dehumidifying the air).<\/h6>\n

<\/p>\n

The post Why don’t we know how much airflow IT equipment requires?<\/a> appeared first on Schneider Electric Blog<\/a>.<\/p>\n

http:\/\/blog.schneider-electric.com\/feed\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

Credit to Author: Victor Avelar| Date: Fri, 08 Sep 2017 18:00:26 +0000<\/strong><\/p>\n

If you\u2019ve ever tried to find how much airflow a new server requires, then you\u2019ve experienced the frustration of burning precious time to no avail.\u00a0 Finding server airflow requirements should… Read more »<\/a><\/p>\n

The post Why don’t we know how much airflow IT equipment requires?<\/a> appeared first on Schneider Electric Blog<\/a>.<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"colormag_page_container_layout":"default_layout","colormag_page_sidebar_layout":"default_layout","footnotes":""},"categories":[12389,12388],"tags":[12391,14591,12398],"class_list":["post-9192","post","type-post","status-publish","format-standard","hentry","category-scadaics","category-schneider","tag-data-center","tag-data-center-science-center","tag-power-and-cooling"],"_links":{"self":[{"href":"http:\/\/www.palada.net\/index.php\/wp-json\/wp\/v2\/posts\/9192","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.palada.net\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.palada.net\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.palada.net\/index.php\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"http:\/\/www.palada.net\/index.php\/wp-json\/wp\/v2\/comments?post=9192"}],"version-history":[{"count":0,"href":"http:\/\/www.palada.net\/index.php\/wp-json\/wp\/v2\/posts\/9192\/revisions"}],"wp:attachment":[{"href":"http:\/\/www.palada.net\/index.php\/wp-json\/wp\/v2\/media?parent=9192"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.palada.net\/index.php\/wp-json\/wp\/v2\/categories?post=9192"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.palada.net\/index.php\/wp-json\/wp\/v2\/tags?post=9192"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}