Economizer Payback Software

[RichL]

Is anybody using or aware of any software out there to calculate the potential payback of adding economizers to existing roof top units? Maybe there's something out there attached to heat loss/ gain software? I have a customer that's interested in adding these but would really like to see a printout showing the expected savings. Any help is appreciated!

Thanks, Rich L

[csbservice]

I would be interested in some feedback on this as well...does anyone use a simple software program...most manufacturer's that I talk to say there are too many variables to nail down an exact figure.....but the customer wants to see some sort of projection---

[larobj63]

Wer use Carrier's HAP ( hourly anaylsis program) at work, and it has both wetbulb and drybulb type economizer as an option for use with air systems.

This software is not fast and easy, but I don't think anything that would give an accurate payback for economizer would be, because it is so closely coupled to historical bin weather data.

We are talking about economizer, and not HRV / ERV, right? Sounds odd to "add an economizer"...

[csbservice]

My application for this right now is with a customer that wants to know in the past 3 years how much they have saved while operating the economizers because they have had about $1500 in repairs in that amount of time....they have asked us to show them the savings of operating them so they know if the next time it fails they should repair or just put in a manual position....if you have a website I could look at to see what you use that would be greatly appreciated or you could email me the spreadsheet or whatever you use- that would be fantastic!

[larobj63]

My application for this right now is with a customer that wants to know in the past 3 years how much they have saved while operating the economizers because they have had about $1500 in repairs in that amount of time....they have asked us to show them the savings of operating them so they know if the next time it fails they should repair or just put in a manual position....if you have a website I could look at to see what you use that would be greatly appreciated or you could email me the spreadsheet or whatever you use- that would be fantastic!

HAP isn't free, actually I think it's pretty pricey... It is full blown modeling software, so lots of inputs are needed to get reliable results.

Economizer doesn't save as much as I would have thought, in short (at least in my climate, might be much different in cooling dominated areas). The longer answer is - there are a ton of variables, not the least of which is the climate (temp AND RH), the efficiency of the cooling system(s), temp set points, occupancy, building use, and on and on.

There may be something out there that provides a quick and dirty analysis, but I don't think there is. Too many variables. I think the only remotely accuarate look at this is with a full blown building / system model...

[RichL]

"We are talking about economizer, and not HRV / ERV, right? Sounds odd to "add an economizer"..."

Yes, We are talking economizer here. The customer went on the cheap when they built the building (Imagine!) and didn't include economizers on their RTU's. They are approximately 5 yrs old. They have a large heat load in the building and are running mechanical cooling at times when it's in the 20's outside.

I can't help but believe that economizers would pay for themselves in short order but I need to convince my customer. If I had a print out from a program I believe it would carry a lot more weight than just my say so.

Thanks for the replies, Rich L

[stanbyyourword]

i should think that if you are able to run your units on low osa temps w acceptable rh conditions then that speaks for itself .I would persuade them to install one econom on one unit then put kw meters or sufficient power monitoring for said unit and a unit of similar load running compressors over a period of time. calculate amount of months a year osa available ,hrs per day etc, worked in w your kwh rates. We do similar w our lpa and cfm/vfd projects, though spreadsheets are good tools , real numbers tell all good luck

[marauderx]

You will need to assume a number of days that the economizer will run based on the internal loads, humidity, and days of weather where running in economizer mode makes sense. This is complicated. Engineers spend days looking into the operation to maximize performance & efficiency, then a few more days figuring out the optimum CFM vs. OA temperature & humidity. It should have a payback sometime down the road, but it may not be for 10 years, especially with having to pay for the economizer being installed on an existing system. It may be better to talk them into replacing the whole thing with something new (less repairs, better EER) and already has an economizer installed with integral controls.

If you can't get a copy of Carrier's HAP, get Trane's Trace. You could probably snag a copy of the older software (Trace 600) from a sales guy, or the full blown new version if your sister-in-law can squeeze it out of him. With the new version you can call the software guys and they might be able to tell you exactly how many days would be good to run the economizer depending on location.

[Control Man]

This of any use to you http://www.micrometl.net/DownloadsLinks/Downloads/tabid/78/Default.aspx try the 3rd one down.