Welcome! Here are the website rules, as well as some tips for using this forum.

Options
Member Posts: 2,343
Solve this problem and go to Bell&Gossett.com and use the calc, that they have. As a rule of thumb only,... Measure your longest run in feet, ad 50% to this, multiply by .04 and that is your pump head required. That is only Rule of thumb. Does not take into account accurate ratings (cv) of valves, fittings etc... I come up with 6ft/hd. remember your length is out and back.....

Mike T.

• Member Posts: 50
Options
what do you think of this calculator

Its for a Trane chiller that needs 100 GPM. They don't give me the feet for the chiller so I am adding a fudge factor. I have 100 feet of three inch copper pipe. Looks like three feet of head. I am doubling the feet of head to acount for the chiller barrel. still not much.

http://www.engineeringtoolbox.com/hazen-williams-water-d_797.html
• Member Posts: 2,398
Options
Not sure if you mean

total equivalent feet of pipe or just the straight portions, but my Cameron's Hydraulic Data (Darcy-Weissbach formula based) has 3" type L copper at 100 GPM imposing a head loss of 2.61 feet per 100 feet of pipe. Of course I have no idea if the return pipe is included or if the 100 feet you cite is one-directional.

The chiller evaporator? That could be ANYTHING from 5 feet to 25 feet. Too much to guess and way too much for a fudge factor in my estimation. I would spend some time tracking that down.

Also and not that you asked, if the chiller is rather close-coupled between pumps, chiller and cooling coils, what is the total system volume? If there is not a lot of distance involved (you did not mention "chiller to cooling coil" piping), there may be a tendency to short-cycle the chiller. You may need a buffer tank.

At 100 GPM I am guessing that the chiller is a 40 to 50 ton unit and could have one large or maybe four small compressors/circuits. The question is, will your water flow through-put be met with accurate turn-down? Just something to think about.
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"

• Member Posts: 50
Options
apt. bldg.

100' is supply and return distance. the close couplled t's are on a loop for the main pump that runs about 300' underground before branching off into 200 apartments. the system total water volume would take as built plans and lots of time to figure but rest assured its large. the chiller is four to one turn down. as far as head in a chiller barrel with the ones were I have seen the numbers its very low but you are right. I should check.
• Member Posts: 50
Options
Grundfos

• Member Posts: 50
Options
Grundfos

Going with the Grundfos Versa Flow UPS80-40/4. I love these pumps I only wish they made some bigger ones. very quite never loose the shaft seal. The pump curv hits 100 gpm 3,5,11 feet of head depending on the speed.
• Member Posts: 2,398
Options
Sounds like

a Two-Pipe H/C system with CHW injecting, so I can see very little excess head beyond the piping and chiller bundle.

Two-Pipe systems of that type do tend to have pretty large water volumes but I have to wonder, for 200 apartments, that is only 0.5 GPM per, barely a 1/4 ton. I bet the management offices get first dibs unless there is another chiller besides this one.
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"

• Member Posts: 50
Options
half way

> a Two-Pipe H/C system with CHW injecting, so I

> can see very little excess head beyond the piping

> and chiller bundle.

>

> Two-Pipe systems of that

> type do tend to have pretty large water volumes

> but I have to wonder, for 200 apartments, that is

> only 0.5 GPM per, barely a 1/4 ton. I bet the

> management offices get first dibs unless there is

> another chiller besides this one.

Its like ahalf mesure granted the apartments are very small but the ones on the second floor never get very cool it only cools the living rooms and not very well. its ot the chiller either. there fan coils are tiny the return water temp is never more than 8 deg higher than the supply to the buildings. I went to a class for commercial load calc. They told us that it is a normal thing to build somthing like this at 75% total load knowing everyone wont call for cooling at once. still its not really enough.I am making the new chiller a bit bigger just because the curent chiller runs fully loaded all day on a hot day.
• Member Posts: 50
Options
half way

The apartments are very small but the ones on the second floor never get very cool it only cools the living rooms and not very well. its ot the chiller either. there fan coils are tiny the return water temp is never more than 8 deg higher than the supply to the buildings. I went to a class for commercial load calc. They told us that it is a normal thing to build somthing like this at 75% total load knowing everyone wont call for cooling at once. still its not really enough.I am making the new chiller a bit bigger just because the curent chiller runs fully loaded all day on a hot day.
• Member Posts: 2,398
Options
Narrow Delta-T

Sometimes and especially on fan coil units, an 8-degree delta-T is necessary to get the capacity out of them. Fan coil coils have only so many rows that can fit in the cabinet, usually only four, sometimes in special units, six rows. Compare these to air handlers where you can get 4, 8, 10 or even an uncleanable 12-row coil. Those can take 10, 12 or even up to 18 degree delta-T's.

An 8-degree Delta-T is nothing to be ashamed of on an FCU job.
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"