Re: [EnergyPlus_Support] Minimum Unloading Ratio

["Jean Marais jeannieboef@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>]

Hi Francesco, Our models in e+ are based on performance curves which show a declining performance (decreased efficiency) due to machine unloading and cycling effects at lower partloads. There is mostly a minimum below which the machine really can't even be on which is as a rule of thumb about 25%, but differs from equipment to equipment. For example, I just had a cost calculation on my desk for an AHU that is supposed to operate at 25 % volume flow...well guess what, although the fan and motor with inverter can actually go that low, the efficiency takes a big knock, but it gets worse...the cooling and heating coils don't need to cool and heat as much and the flow in the coils starts drifting into the laminar region. Consiquently, the performance makes a big spike over the transision and could cause erratic behaviour of the control valves which may also start trying to opperate outside their control bands. Despite the internal pressure drops of the AHU being far less, it actually costs more to run than a machine sized for the small amount of air. Anyway, I just wanted to say that there's always a bit more to it than the obvious and it's good to try and keep a wholistic view of things.Best regards, Jean.

2016-10-05 11:53 GMT+02:00 fpasserini.tn@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>:

 

Hello, if a chiller has 4 scroll compressors, then the Minimum Unloading Ratio shall be 1/4 (i.e. 0.25), correct?

I want to be sure, because in a model that I'm considering the chiller is oversized and the Minimum Unloading Ratio influences a lot the annual consupmtion.

Regards

Francesco

 

__._,_.___

---

Posted by: Jean Marais <jeannieboef@xxxxxxxxx>

---

EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx

The EnergyPlus web site is found at:
http://www.energyplus.net/

The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/

Attachments are currently allowed but be mindful that not everyone has a high speed connection.  Limit attachments to small files.

EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.

Visit Your Group

• New Members 11

• Privacy • Unsubscribe • Terms of Use

__,_._,___