criteria for % of design capacity vs installed capacity?

[mateno]

Hello?

I am working with a condo-hotel hvac design, i already calculated the total capacity (Tons) the building will need. I think that in order to reduce the co$t of installed equipment(Chillers) we can maybe install only a percentage of the total design capacity because of the Usage/schedule factor of the areas. What is the % of design tons you recommend to be installed in a hotel building?

Regards

 

[DrRTU]

I would prefer to design to 100% and then alter the design assumptions such as lowering the OA conditions, interior shading types such as drapes and misc. electric loads. After I see how the model responds to the change in assumptions next look at the sizing of the primary plant. For example I would use a 1% day for the OA and very light shades and lights on with no diversity as the max peak. Then lower the OA and add heavy shading and no 50% on lights as min. peak.

 

[AbbyNormal]

Maybe the problem is, "What is 100%" in the first place.

You do a commercial building, the softawre will find the peak load, you can size for that.

A lot of time the residential type of calcs, sort of average morning and evening, east/west.

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[HVAC68]

Trust you want to know what the "diversity factor" should be.

Have you done your load calculations in a software and the inputs include proper scheduling for all loads including lighting, occupancy, etc., and the software calculates hour by hour for the entire year ?

If yes, the software will find its peak load. You can even check and find out how many hours this peak load would be there and take a judgemental call as to the diversity to be considered. As a rule of thumb, 0.75 to 0.8 diversity factor is what I would normally consider. But, again it depends a lot on the client inputs, your own assessment of the project and the confidence you have in the inputs.

HVAC68

 

[ChrisConley]

If you're really looking for diversity, find out exactly how many days per year that the hotel is prepared to have uncomfortably warm guests. If the answer is zero (which is my guess) be very careful with diversity calculations.

Systems have a way of simultaneously peaking at the worst possible time (kind of an HVAC Murphy's law). Clients, during design, are prepared to put up with all kinds of discomfort, occupants are much more picky.

 

[DrRTU]

You have to be very careful with the DF on a hotel project. A hotel DF will be vastly different than a VAV office building. Look at how the facility operates. With an automation system, the guest room could be in a setback and just as the space/building peaks, the guests will be entering the rooms. As a guest enters, they lower the sp and now you have hundreds of small fan coils calling for max cool. Your loads were most likely based upon steady state and not on pull down. Pay attention to capacity of the fan coil. Your loads may only have been 9,000 BTU/hr but you selected a 12,000 fan coil. The chiller now is trying to match an increase the load by 30%. I have done a few D/B projects and was quite surprised by the peak loads. I know Marriot has a selection criteria that the chiller plant should x times the connected / calculated peak load.

 

[willard3]

I have been involved in fixing lots of buildings that have had diversity factors applied that were unrealistic.

Diversity factors just shift undersizing risk from the owner to the Engineer.....

No body will thank you for being hot/cold in their new building.