[AusNOG] Data Suburb

[Tony de Francesco]

Thanks very much for that analogy as it precisely highlights one of the
reasons why the "reduced efficiency at part load" argument gets so much
traction with people, i.e. people think they understand the technology and
find over simplified examples to justify their position.

 

If you will allow me, let me educate on how an air conditioning system (and
not a V8 engine) responds to part load operation:

 

Let's look at an air conditioning unit that is designed for 1000kW of
cooling, but is delivering only 200kW of cooling:

 

a)       Firstly when operating at a full 1000kWs of Load:

a.       Refrigeration System Power Use:           EER of 3.5, equating to
around 286kW of absorbed power

b.      Air handling System Power Use:            (relates to 69,000m³/s of
supply air based on an equipment ΔT of 12°C) equating to around 60kW of fan
power

TOTAL = 346kW of power use or a pPUE of 1.346

 

b)      The same system at 200kW of Load:

a.       Refrigeration System Power Use:           EER of 8 (as the
refrigeration COP improves at part load), equating to around 25kW of
absorbed power

b.      Air handling System Power Use:            (relates to 14,000m³/s of
supply air based on an equipment ΔT of 12°C) equating to around 1kW of fan
power (as per the fan laws). 

TOTAL = 26kW of power use or a pPUE of 1.130

 

So you can see in this example at 20% load utilisation, the pPUE (i.e.
cooling system PUE) should be around 1.130 and increase to 1.346 as the load
approaches 100%.

 

This correlation is often not the case with electrical systems, such as
static UPS and DRUPS units, which tend to have lower efficiency at part load
and better efficiency at full load (as per your V8 analogy).

 

However, the improvement in the cooling system PUE at part load generally
offsets the reduction in electrical system PUE at part load and so the
overall facility PUE remains static over the load utilisation range.

 

Hope this helps your understanding although please feel free to email me on
or off list if you would like me to explain any of this in further detail. 

 

 

 

Kind Regards

 

Tony de Francesco
Technical Director

email: tonyd at pue.com.au

mob: +61 (0) 457 701 179

.....................................................

 

  _____  

From: ausnog-bounces at lists.ausnog.net
[mailto:ausnog-bounces at lists.ausnog.net] On Behalf Of Luke Smith
Sent: Thursday, 5 January 2012 11:16 AM
To: ausnog at ausnog.net
Subject: Re: [AusNOG] Data Suburb

 

>  This statement has permeated the industry and led to people accepting
lower levels of efficiency at part load in the hope that their PUE will
improve as the load increases.  There is no technical reason why PUE has to
suffer at part utilization, other than people accepting a facility design
that allows this. 

Applying an analogy... if this were the case then you should also expect the
same economy from a 6.0l V8 as you get from a 2.0l four in the same car. But
the world doesn't work like that.

 

Unless its *very* modular and you can totally turn off the bits you are not
using then you simply can't expect a half used facility to have the same
efficiency as a fully utilised one half the size. Going back to the analogy
modern V8s have cylinder deactivation that saves some of the overhead, but
they still waste energy spinning a few extra cranks and pistons about that
they don't need 99% of the time.

-- 
Cheers,

Luke Smith
0419 671 006

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