High Rise Piping Design

[Daryl1126]

Currently working on a renovation to a 40-story building which has a low and high zones for the HVAC hydronic piping. The client rep would like to install a single zone. Does anyone have experience with this type of zoning? We prefer to maintain the existing zoning.

 

[ChrisConley]

What do you mean by high zones and low zones? Perimeter and core zones?

Without knowing to much about your system I would say that a single zone serving an entire floor is going to leave the occupants unhappy, regardless of what the owner says.

 

[Daryl1126]

Chris,
sorry for the lack of information. The "low zone" serves floors 2 to 21 and the "high zone" serves floors 22 to 41. The existing system is a reverse return.

 

[ChrisConley]

My personal experience is that, due to stack effect in taller buildings (such as this one) the low zones have a much higher infiltration load. As a result it is usually beneficial to provide a seperate 'zone' for the lower floors.

 

[HVAC68]

Must be long quantities of piping with reverse return system. You could avoid reverse return if feasible at this stage and have balancing valves installed. There are automatic balancing valves which would make the balancing a lot more easier - Try TA Hydronics - they may be able to help you with the balancing valves.

With high rise buildings and lots of tap-offs, branches, FCUs, etc., balancing is a nightmare.

HVAC68

 

[SAK9]

Assuming a height of 4.5 for every floor,the system static pressure at the ground floor will be about 19 bar with a single zone piping arrangement.Since the system has been designed as two zones,the lower floor obviously would not have been designed to withstand this pressure.If you go through the operation manuals,you could get some data on the valve and AHU coil pressure ratings and can confirm the max pressure theu would take.You need to examine the pumping arrangement(draw thru or pull thru)to see the effect of higher pressure on the chiller tubes.There is a cost penalty for high pressure rated vales ,coils and piping if you use a single zone apart from the difficulties of balancing a large system.I would suggest you query the owner why they want to go for a single zone system.

 

[friartuck]

I have come across this problem before. It depends what equipment you are using. etc.

Fortunately there aren't too many high rise building in the UK, so we don't have a lot of experience on this. The highest I have worked on is about 14 storeys.

High quality radiators will work at about 7 bar (70m head approx) so this I guess would equate to 14 stories. So I assume you would (based on this principle) have main plant rooms at 14 storey intervals. (i.e. zones up to 14 stories).

If fan coil units are proposed, then these can work at higher pressures (i.e. 10Bar or more) , but the fittings also have to be equivalantly rated or leaks will occur.

I would guess you have a lot of heat exchanger units at the 'zone' plant rooms with major plant either on the roof or in the basement (depending on what it is. I suppose rooftop plant is preferred for getting exhausts away and ejecting heat from towers and so on.

I have seen some projects use PRV pressure reducing valves and safety valves (to take out the excess pressures)but I don't like that idea.( too much unreliability and maintenance)

Is there anyone out there who has designed a really high building...if so, what did you do??

I am really interested.

Friar Tuck of Sherwood

 

[jherbert]

The primary reason for verticall spliting zones in high rise building is the statis hd, and hence the cost, and delivery. Incidentally, this principle also applies to fire services installation in high rise buildings.

For example, taking SAK9 4.5 m floor to floor

If the chiller is at a low floor, the evaporator, pumps and lower floor equipment would need to be rated at 4.5m x 40 = 180m static hd + margin.

If the chiller was located at the roof level, the AHU coils/FCU coils, etc. for the lowest floors would suffer 180m static hd. + margin.

I design high rise buildings in Hong Kong, and split the vertical zones to avoid excess static head. That saves buying "specials" chillers, pumps and equipment, which also tend to have much longer delivery periods - that how it is done.