Fans - Full Load Energy Rate

3 posts / 0 new
Last post

In the Trace 700 + LEED training example, the fans in the proposed model were in locked in at their nominal horsepower. I do not fully understand how Trace uses this information.

When the nominal hp is set like this, does Trace use the unloading curve and fan efficiency of the particular library member selected under "Type", and then project that fan's performance across the modeled operating conditions?

I want to make sure that I am still getting credit for using an efficient airfoil fan when I lock in the nameplate hp. I had initially thought that, if we have an efficient fan, that setting the full load energy rate to kW/ CFM-in wg would yield greater savings than setting the nominal hp.

Thanks!

lowedogg's picture
Offline
TRACE 700 User
Joined: 2012-03-09
Reputation: 0

Your initial thought was right. The thing is that TRACE ultimately determines the KW draw of the motor. Thus, an efficient fan will have a better kw/cfm-in wg, and given the same cfm and static, it would have the lower KW or hp.

In general for LEED, you should already have equipment selections and thus you should enter the data to match what you have in your selection.

On another note, the fan type does refer to the unloading curve, but this really only matters if the system is variable volume. In a constant volume system, with the fan set to "cycle with occupancy" (per LEED). The fan will operate at full load for 100% of the time that the building is occupied.

This is where selecting a high efficiency fan (and rightsizing) will allow you to lower the total hp or KW from that fan. Since given all the conditions are the same - a high efficiency fan will still have the lower kw draw.

Sometimes constant volume fans also come with a VSD, especially if they are oversized and then they are calibrated on-site. It is useful to have this data to submit to LEED because the fan may be nominally 50 hp, but in reality it is set to a certain CFM and only ever operates at say 30 hp. This would be a 40% savings in a CV system.

Bob's picture
Bob
Offline
eQUEST UserLEED AP BD+CTRACE 700 User
Joined: 2010-06-30
Reputation: 275

Thanks Bob. So I ended up creating library members of my proposed fans based on the installed equipment. Within the library member I defined the full load energy rate and specified an unloading curve. I then entered the nameplate horsepower in the fans tab.

I can see in the Equipment Energy Consumption report that Trace is in fact calculating the energy use based on the fan's library characteristics.

lowedogg's picture
Offline
TRACE 700 User
Joined: 2012-03-09
Reputation: 0