Designing HVAC Expansions

Headed to the AHR Expo 2014

As I write this month’s blog, I am getting ready to attend the AHR Expo (Air Conditioning Heating & Refrigerating) Jan 21-23 at the Javits Center in New York City. I don’t know why I look forward to this show so much each year, I guess because it’s our first trade show of the New Year and it is always well attended. 

At every trade show, we get to meet many of our existing customers and have an opportunity to talk to people who are interested in finding out how PIPE-FLO can help them do their job more efficiently.

The most often asked question at the AHR show is “I’m adding on to an existing chilled water system with a new (wing, building, etc.), can I get by just modeling the new addition, or do I have to model both the existing system and the new portion?" 

They often know the answer, but they ask anyway.

No matter how often I am asked that question, I always put my hand on my chin and count to five before giving a response. You never want to give an immediate answer, if you do it sounds as if you haven’t given their question any thought. 

After my thought-provoking pause, I respond with “It depends.” 

They immediately respond with “What does it depend on?” 

I then answer with “Do you want to do it right and get more business from this client, or do you want to do it fast and find another client to work with?”  

Now that you know my answer, I’ll explain further.

 

The Life of a Large Commercial Space

Large commercial building, campus, and business parks are always in a state of change. New tenants move in and out with different heating & cooling needs, new equipment is added to the system, and new wings or building are built. Often these new loads are added to an existing system, and as we say in our Piping Systems Fundamentals course, any change made to any item in a piping system effects the every item in the system. 

For example if you want to tie into an existing system the client may provide you with the pressures at the supply and return header where the proposed tie in will occur. They figure the designer can use this as boundary pressures when modeling the new expansion. The problem is when the new expansion is tied in (both supply and return header) fluid will be going to the new building resulting in a reduction of pressure where the tie in occurs. Not only does this affect the new expansion, but it affects the existing system as well.   

Future expansions are often taken into account when designing new system, the mechanical room is sized to accommodate additional chillers and pumps that may be needed for future system expansion. However, when a new building is added to an existing system the existing system must be factored into the new design. Once the addition is completed, the commissioning crew must balance the entire system (both the existing loads and the new loads). If only the loads in the addition are balanced, the loads in the existing system will have less flow than needed. Often these problems don’t show up until multiple additions have been accomplished, and the heat load on the building is in the worst cast conditions. 

During system modification, the flow rates in pipelines may increase to the point where a small change in flow can have a major increase in head loss. This results in a bottleneck and if they are not considered additional pump are purchased and added to the system in an attempt to get the flow to what is required.  Someone often comes up with the idea of adding a booster pump to the building to “fix a low flow problem”, this often causes more problems than if fixes.  That is how bad things can happen to HVAC systems by just looking at the additions.  

 

Giving the Customer What They Really Want

A building owner wants to rent out space in their building and have happy tenants that pay their rent on time. If a new tenant needs to change the space, they pay for tenant improvements, things like new lighting, walls, etc. If they are adding new heating loads, computers, new medical equipment, etc. they may need to pay for modifications to the chilled water system in their office space as well.  However, as we saw earlier when any change is made to the system (even if it is just in their space) it affects the entire system, impacting the spaces of the existing tenants. 

As time goes on, changes are made to the original building to meet the changing tenants' needs. The market is good so it’s time to consider adding that second wing to the building. If you don’t do it right (simply look at the new wing without considering the impact on the existing building), then the temperature in your customers spaces will move to the unhappy range.  

The best way to keep the tenants happy is to evaluate the entire system each time new loads are added or removed from the building HVAC system. 

Now an engineering firm is in business to obtain customers, get the job done on time and under budget, and leave the job with a happy building owner. The engineering firm should realize that any building that has been in service for any length of time more than likely has problems due to previous system modifications. That fact will make it more difficult to tie in the new expansion to the existing system. 

Since the engineering firm sell hours, and you know the clients wants to have happy tenants, why not share with them system expansion horror stories. Then suggest the client may want to include the modeling of the existing system to the contract. This will let you identify and correct existing problems, evaluate the entire system (both existing & expansion). While you are at it, you may suggest that they want to look at what can be done to minimize the power consumption. Who knows, maybe the local utility will pick up some of the cost?! All these things and more can be done when there simulating the operation of the entire system.

Then when the commissioning of the new system goes off without a hitch and all the tenants are happy your client will thank you for doing such a great job and have you back when they add that third wing.

If you would like to see how PIPE-FLO is used in the HVAC market to commission and balance loads, troubleshoot existing systems, or design system expansions stop by our booth at AHR and we can talk and share some stories.  If you aren’t going to be at AHR give us a call and sign up for a Webinar so you can see how PIPE-FLO simulations are being used on HVAC piping systems.