Refrigerant piping length

[hhjlep]

I am new to HVAC design and need help on the following issue:

I have specified a number of house hold Split Units for an office complex. The split units are relatively small, most of them providing 3.2 kW of cooling. I need to run the piping for 25 - 30m, as the only available space for the condensers are at that distance. On the data sheet, it states that the piping length should not exceed 20m.

My questions:

1) How much would the efficiency typically drop if I would exceed the max piping length by 5m
2) How much would the capacity of the unit drop if I would exceed the max piping length by 5m
3) I have over-sized ALL the units by about 20-30%. Would this "contingency" be enough to deal with the extra 5 - 10m of piping?

Thanks

 

[Waramanga]

check the engineering data books for the performance drop. going further than the specified distance doesnt just reduce capacity, it affects oil return and it kills any warranty that the manufacturer might have. Dont do it. You need a VRV system for this length of pipe or a super multi.

 

[hhjlep]

Did not realize that one can damage the equipment by using longer pipes than specified. The 5kW units can tolerate pipe lengths of up to 35m, so I'll over-size all units to at least 5 kW. The client did unfortunately specify that a VRV system is not an option as this would complicate maintenance and storage of spare parts.

Thanks!!!!

 

[HVAC68]

1. Is the 25 - 30m horizontal or vertical ?
2. Is it the equivalent length ? Have you accounted for the fittings ?
3. Apart from specifying the maximum length, the manufacturers also indicate the maximum vertical lift allowed.
4. Best way forward would be to get a back-up confirmation from the manufacturers on the maximum allowable length (vertical and total) along with the drop in capacities for the length specified.
5. Split units for office ? How big is it ? Where does fresh (outside) air come from ?

HVAC68

 

[hhjlep]

HVAC68, herewith the answers to the questions that you have asked.

1) The 25 - 30m is horizontal
2) Yes
3) There is no nett vertical lift
4) Thanks, I would consult the supplier on the capacity drop
5) Fresh air is provided by means of a fresh air supply duct. The offices are small, in the range of 20m^2, therefore the units are sized at 3.2 kW and 5 kW.

Some background: This is a small offices complex within the concourse area of a large station. The client has requested changes to a HVAC system that was designed previously. I was not part of the previous design team, so I am changing the design to client specification. They requested the use of split units wherever possible.

 

[HVAC68]

Check with the manufacturer for the pipe sizing and the capacity drop. I don't see a problem if you get a confirmation from the manufacturer on the maximum allowable length, capacity drop and pipe sizing.

Trust the fresh air supply is treated and not untreated. Untreated fresh air can cause condensation.

HVAC68

 

[imok2]

For 134a or R-22 at 100 ft you can use 7/8" suction and 3/8" liquid line at no appreciable loss in capacity