Hospital Essential Electrical System Rule of Thumb 3

[lile001]

I've been told a quick rule of thumb for emergency generator capacity for hospitals is about 6va/square foot. (Obviously, good load calculations and historic measurements are the only way to know for sure.) This is only for doing a preliminary guess at a generator size, accurate load calcs will be done later on. Does anyone have any examples that can reinforce or debunk this theory? How about a recent project where you know the actual generator capacity and the actual square footage of the building for comparison? This would be a full-blown hospital with all the trimmings - surgery, emergency departments and so on.

 

[l3city]

Hi there!! Well NEC Art. 517(B)(2) states in part that "the emergency system shall be limited to life safety and critical patient care." You might as well include some emergency lighting to be operated via Generator. However, you have to consider that if you apply a "rule of thumb" you might be over-designing (and ya'know, a generator is not that cheap) So, take a closer look to NEC-517 and start from there.
Regards

 

[EEJaime]

We use a combination of factors for preliminary utility/genset planning. We just completed a Central Utility Plant installation for a new Hospital facility. The construction is to be phased so we don't have all the verification in as of yet, but we are very close in the areas which have been complete.

You need to be very careful in the early stages of planning that you include all the loads which will ultimately be fed by the EPSS. In California we have specific loads which are required to be fed by the two branches of the Emergency Power Supply System, (Life Safety and Critical Branches), as well as the Equipment Branch. In some cases such as that we have recently finished the Facility Planning and Physical Plant management there are additional systems which a facility may want on the system which are not specifically required to be connected by code and which must be on a fourth priority branch.

We learned too late that some imaging systems now require higher levels of emergency power than in the past, (we had to add additional distribution capacity). Some factors we use are:

Surgery Center/Acute Care Hospital-6 va/sf
Medical Offices-1.5 va/sf
Radiation Therapy- 4 va/sf
Central Plant- 10 va/sf
IT Building- 55 va/sf
Administration- 1 va/sf
Parking Structurs- 0.5va/sf

We have validated all of these in the past and the figures provide a good guide to preliminary planning.

Good luck with your project.

 

[itsmoked]

Hi EEJaime; Nice table.

What about those imagining loads? What's the va/sf for an MRI imaging suite? Same as radiation type loads?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[EEJaime]

MRI systems are very load intensive and the loads are not the traditional short spike type of loads as with traditional x-ray equipment. The majority of the MRI systems we see installed are by GE Medical followed closely by Phillips. It is not always required by the facility to have an MRI system on emergency power because of the high loads involved. Often times we use a UPS system for the MRI units. This gets very expensive and space intensive. The last system we did, (it went on-line two months ago), used a GE Twin-speed II, 1.5 Tesla unit. The system load is 94.3 kVA plus 15.8 kVA for the cooling system. The since the MRI suite is about 800 sf, you can seet that this is a very load intensive space.

 

[itsmoked]

Thanks EEJaime.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[stanlsimon]

Consider the snowball effect of including an MRI on the emergency power system, without the Hvac system and other ancilary equipment the MRI won't last very long.

How about a separate transfer switch to the equipment branch? Hospital administration should be involved in a decision like this. Hope they understand what you are talking about.

 

[itsmoked]

I could see where an earthquake might drop the power for several days,(like it did here), and simultaneously create a lot of people needing MRIs. Though maybe a separate generator would make more sense.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[EEJaime]

One of our major medical clients in California has allowed individual facilities to dictate how much equipment is on emergency power. At the facility just completed, we have a branch of emergency power which is a fourth priority branch feeding a substation supplying all x-ray and other imaging systems in the hospital. We connected to that branch. The problem is that MRI power quality requirements from the manufacturers are extremely tight. After taking recorded load and power profile readings on this branch, we could not guarantee that the power would meet GEMSCO's specifications. As a result we installed a full double conversion UPS system which cleans up any power quality issues. At the cost of a piece of equipment about 9 ft wide, and 36" deep plus a maintenance bypass switch and power distribution unit, oh, yeah.... and about $260,000.00. Can't forget that.