Power consumption in the office building

[crisleon]

I would like to ask you about the real power consumption for the A-class office building.
The problem is that we designers have to prepare the application to the grid operator here in Warsaw, Poland, for technical conditions for supply for such a high-rise tower of about 70,000 sq. meters (total gross area in the over-ground part) plus about 10,000 sq. meters in the underground parking. Of course, the most important information is the power requirement for the whole property.
Roughly speaking our simplest formula states 100-120W/m2 for offices, what gives something like 7,500kW for everything (including air-conditioning, ventilation, lighting, computers etc.). More detailed calculations lead to the similar result and the simultaneity factor about 0,55-0,6 what we are likely to take into account.
However it seems to be a bit too much. My question is: how many kilowatts the Client should order in the utility company to be on the safe side (to cover all needs) and - what is not quite least important - not to have too big the due payment for the connection to the electrical network and future exploitation costs (the company will burden with payment for the readiness to the delivery of the energy at the given level of demanded power).

Have anybody true data from real experience and from power monitoring system? Available not from manuals or guides but just from real life? I’ll value all prompts and information (total power loads versus total gross area of the modern office building anywhere in the world).
The best regards.

 

[rbulsara]

For real numbers, ask the local utility company or some facilities managers in Poland. If not on this forum, you may find some managers on sites like LinkedIn.

Rafiq Bulsara

http://www.srengineersct.com

 

[crisleon]

RBulsara,
thank you for your advice. Haven't you any own experience in this topic?
I have some data, of course. Designers are likely here to do prior estimation at the higher level than it is in the real life (similarly, some guides and publications). However this is not so stupid because the danger is that in our climate there are some hot days in the summer when electrical power demands climb up because of air-conditioning. In such days such expectations of very high energy consumption may come true (the utility company punishes then the client with additional charges, according to the contract).
For that I'd like to hear about data from other countries, esp. where there is the hot environment (climate) and more technically advanced infrastructure.
Regards

 

[WoodrowJWeen]

120 W/m2 sounds about right for connected load of a typical office bldg in southern part of US with electric heat. (Yeah, had to think about the metric conversion) Demand figure used by power companies is probably in the 0.65 range around here, maybe less.

 

[rbulsara]

I do, as a consultant, in Eastern and Northeastern USA and it may not be relevant in Poland. Plus I don't know what is in "your" building or your climate. Computer loads and type of lighting used makes a difference.

In the USA, engineers appear to design the building service to say 10W/sf (90-100W/m2) and actual demands end up closer to 6 or 7 W/sf (60-70 W/m2) for a fully air-conditioned building with fair number of computers and efficient lighting. Plus there are minimum codes for service sizing in the USA. Utility company routinely provides much smaller size transformers than engineers specify, but they can change it too when required!

Climate has a great influence too.




Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

In Canada the code does not allow any diversity factor to be allowed for air conditioning loads.
But due to the moderate climate in Canada, air conditioning tends to be sized smaller than in hotter climates and will always be running at 100% on the hotter days.
This is to illustrate the danger of transferring data from one area of practice to another.
There is nothing wrong with comparing installations from widely differing area and climates but be aware that the figures from other areas may be influenced by engineering practices in other disciplines than electrical.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crisleon]

If you suggest that 60-70 W/m2 is not bad I may say that I think just also about such a coefficient. Bluntly speaking I am afraid that I may make the mistake to undervalueting the toatal demanding power (the risk of the discredit).
Regards.

 

[davidbeach]

Take your best stab at the initial loads, and then add about 25% for future unknowns. Things happen, never try to make the electrical service as small as you can get away with.

 

[rbulsara]

I did not say 60-70W/m2 is not bad. I would not design to it.

This is one of the reasons, I hesitate to throw out numbers, as someone may just pick what he/she likes. It is not a matter of what sounds good to you, you need to design to what may actually be appropriate. For a variety of reasons, including what davidbeach mentioned, I personally do not like to size the service equipment to bare minimum. In fact I hate to see main switchboard running more than 60% of its rating. Transformer sizing is something different.

Diversity factor is somewhat of a black magic, that only comes to you with experience or better knowledge of the system and load profile.



Rafiq Bulsara

http://www.srengineersct.com

 

[crisleon]

I thank everybody for your advice and information.
Rafiq, don't hesitate to talk about such things as I consider. I am an experienced designer and I won't do such mistakes as you mentioned.
I am in contact with people from the utility company and I know some data. I want to verify this quantities with other people and their knowledge.
A few months ago I prepared application to the grid operator for other office buildings, also over 75,000m2 in total area plus parkings. After some calculations and data from HVAC designers I took 8500kW as the total demanded power. Then the guy from the utility company told me that in the similar facility of similar area the maximum power consumption was circa 5000kW. After hesitation I corrected to 6500kW. Life will check it.
Regards.

 

[waross]

A note on utility transformer sizing.
I was involved with the design of a mill where the loading was almost 100% motors.
The transformer could be customer owned or utility owned. If we owned the transformer we got a better rate for power.
BUT
If we owned the transformer it had to be sized based on 100% of the motor load in KVA.
1000 HP needed about 1039 KVA plus other loads that resulted in a transformer size of 1250 KVA.
The utility was not bound by the same codes and sized the transformer at 500 KVA per HP resulting in a transformer of 500 KVA or 750 KVA.
WE as designers are expected to design a system that will work and last into the future.
The utility may easily change out a transformer if the transformer is overloading.
Also, the main service in both cases was sized for about 1250 KVA or 1500 KVA, regardless of the transformer size.
Our code for office buildings is based on 50 Watts per square meter at 90% demand for service conductors and 70% feeders.
Plus other loads.
Special lighting, special power loads, parking lots, A/C, heating, mechanical, and elevators.
Note, a large number of small UPS units may demand more than their nominal rating when all are recharging after a power outage.

Bill
--------------------
"Why not the best?"
Jimmy Carter