Economizer payback software

klaus

Is anybody using or aware of any software out there to calculate the potential payback of adding economizers to existing roof top air 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.

Thanks, Rich L

don_185

Do you

Do you really want to go down that road?

If you do not live in a dry climate then you will have to
consider a enthalpy control.

Also factor in learning how to operate and maintain that enthalpy control.

I know for years when we used them we had nothing but issue with the sensor,humidity and people that had no clue on how they were suppose to work.

Beware!

Mike T., Swampeast MO

Here's the closest I could find.

Yes, they can save when functioning properly but they are well known for never working properly to begin with as well as becoming a maintenance headache.

Notice that components and controls of the finest quality are suggested for effective operation over a reasonable lifetime with reasonable maintenance.

Since they draw outside air which is often much dirtier (and I'm not even mentioning insects), I have heard suggested that they must have a pre-filter and that the only "proper" pre-filter is a motorized, automatically advancing roll filter which only adds more cost and complexity.

Methinks that economizers are best used in applications where proper maintenance is a near guarantee--say a full-time, qualified superintendant or a long-term service contract that guarantees routine maintenance.

VERY easy for economizers to waste more energy than they can save when improperly installed, controlled or maintained. Unfortunately most wind up with all three problems and are abandoned when bills (maintenance and fuel) go sky high.

klaus

Thanks

Thanks for the replies Don and Mike. And yes, we absolutly want to go down that road!

We maintain numerous facilities with RTU's that have economizers. These are on commercial buildings with high lighting, computer, and/ or occupant loads. In our area, Eastern Iowa, we have lots of summertime humidity so we use full enthalpy controls. I believe economizers are a nice "green" solution to cooling in low ambient conditions. It makes much more sense to me to bring in cool outside air on a chilly November day for a cooling call than to bring on the DX with all the ambient controls. When explaining it to a customer I equate it to opening a few windows, in a controlled manner, if it's cool outside and it's too warm in the building. Most owners like and understand that. If they think they're going to save money with it, and they are, they really like it!

I think every economizer we install or maintian has it's own pre-filter Mike. These are of the washable screen variety that basically just stop bugs, sticks and small children from getting into the main filters. Those filters in turn do have to be changed more often in the shoulder seasons but those costs are built into the maintenance agreement.

I would think there would be software out there that would take all the factors into account and give an expected payback on this investment. If not, I guess here's an oppertunity for a developer!

Thanks again for the replies, Rich L

Elmer Fudd

Economizer payback

Economizers do not make sense in all climates. Where I live (midwest)they make sense. there are many days even in cooler weather when the sun is shining that buildings need cooling. I have surveyed buildings and seen air condiioning cycling on cold enough days to use the "free" cooling. I have not seen any data on reduced compressor life from this.

I do not like or use enthalpy economizer controls. they are complicated, require maintenance and often do not work well. An outside air temperature economizer is overall the simplest and cheapest to use. You loose some energy savings and maybe some comfort on some days but easier to work with and maintain.

there are energy savings. The simplest way is to assume the compressor uses 1 kw/ton(RTU's are probably more depending on age but 1 is a simple number to work with), figure out about how many tons, estimate how often the AC works versus being able to use outside air(hardest number to come up with) and you will need to know the electric cost. if you have multiple compressors or stages use the lowest estimated tonnage size that it would take to run in the winter(take a good estimate.) for example 1 KW/ton x 5 tons(assume one compressor on/off) x 20,000 hours/month compressor operation ( I deliberately made this number ridiculous- you need to estimate the run time based on your experience and what the unit serves. it will be more in some months and less in the middle of winter, interior spaces may need constant cooling all year long, south exposures, lots to consider) x 10 winter monthes it could be using outside air (you need to figure how many pracitcal months you can use OA. where I am we could probably use most of september to april) x $2/KWH(ridiculous number) = $2,000,000/year. simplistic way to look at it but that is the basics. there are probably better programs to do it(I have an old spreadsheet.) I may do an web search just for the heck of it.

The dampers are some maintenance just like any other piece of control equipment. they can stall open or not close totally and cost more energy to use or freeze a coil. OVerall they are one of the most overriden controls on an air handler. it is easy to manually close and forget them then fix or trouble shoot them. this often leads to stinky indoor air and overheating problems in areas.

Most of the RTU economizer packages I have seen use the outside air as a first stage and only if the space cannot be kept cool does it start the cooling. I do not know how well economizers work on smaller roof top units. I would contact the manufcturer and see what they recommend.

[Deleted User]

We have used the Honeywell products on quite a few projects and have worked well. you can expect some humidity sensor replacements over time. when you are thinking of saving on power you also have to think about compressor life with reduced run hour. Get with your Honeywell commercial rep for the software. they should be able to provide it to you or the link on the wesite.