Cost Comparison of a VPF Chiller and a Normal Chiller 1

[Buildtech2]

I would like to know the difference in the cost of a chiller suitable for variable primary flow system and a normal chiller for commercial chilled water system. According to the local Trane representative, there is no difference in the price of a two chiller types but other says there is a 15 % to 20 % difference in the chiller cost.

Please advice.

 

[DRWeig]

I don't know why the cost might be different -- unless the premium is for a variable speed drive on the chiller itself or for chillers that can handle lower minimum flows without freezing up. Not sure how they'd do that, I'm a controls guy not a mechanical engineer.

However, working with mechanical engineers and Trane/York/Carrier reps, we have converted existing plants that have constant-flow primary - variable flow secondary to all-primary variable flow. No problems, and existing chillers were used.

Best to you,

Goober Dave

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[EnergyProfessional]

The Trane rep who actually knows the prices, just because someone on the internet says something different... go with the rep.

if hte chiller was designed with variable flow in mind, there is no cost difference

 

[SAK9]

The question you need to ask yourself or that Trane guy is what is the difference between a VPF and Normal Chiller.For a chiller to have variable flow,it needs high water velocity through the tubes so that the flow never goes into laminar region.Understand how this is achieved in a VPF chiller and you have got the answer to your question.

 

[Buildtech2]

Thanks everyone..

I am in the final stage of my thesis where I have to perform economic analysis of three different chilled water pumping schemes. I have already completed energy analysis with Carrier HAP. Three types of chilled water system configurations will be modeled in a typical application. The performance of conventional systems (constant-flow-primary-only and constant-flow –primary / variable-flow-secondary systems) will be compared with sustainable systems (variable-primary-flow system). The following performance factors shall be evaluated and compared with each other to quantify the energy and economic advantages of sustainable systems over conventional systems.
• Energy consumption
• Energy cost
• Life-cycle cost
• Simple payback period

Now if the cost of a VPF chiller is 15% to 20% higher than a normal chiller, there won't be any considerable difference in the life cycle cost as chiller is the most expensive equipment among all. So accurate information about chiller price is very important.

 

[Drazen]

sak gave you crucial input. you need to verify it with manufacturer's rep if you want your comparison to be legitimate.

some effort is always needed to swim through ocean of commercial talks and get right technical information.

 

[EnergyProfessional]

most newer heatpumps, chillers and boilers are tested and approved for variable primary flow and the manufacturer can tell what minimum flow is. There isn't a very same chiller that has variable flow as a " 20% upcharge option". so you can't compare apples to apples... if 2 chiller models cost different and the one is variable flow approved and the other isn't, chances are there are other differences as well responsible for the price difference.

I don't know every device availabe, my statement is just based on the ones I deal with, but for those there isn't n option. My experience very small devices (i.e. boilers under 750,000 btu/h) are designed for primary/secondary flow (you can do varaiable primary, but it gets complicated), the larger devices are for variable primary flow by design and not as an option.

You also save on pump, piping, wiring and space by not having primary pumps. and unless you lead/lag each primary pump, overall pump reliability will be higher with variable primary flow.

 

[Waramanga]

Why get hung up on the exact cost of a chiller? You will never get the real price until you are ready to place an order anyway, a simple % difference in cost would be as useful as an actual number. What kind of analysis of part load performance are you doing? Condenser water temperature? Chiller load?

 

[urgross]

I did a variable primary plus distributed secondary chiller plant about two years ago. I saw no basis for added cost for the same type chiller based on the same bin data, which was confirmed by the Trane rep.

Largest differences were for pump sizing, minimizing size of distributed booster pumps, and added costs for pump bypasses (existing system was a constant primary/constant secondary of 1970's design), additional dP's, and higher cost of pressure independent control valves.

It would also depend on your central plant configuration and chiller sizing. With LCCA and full bin data, a smaller chiller with VFD and two larger chillers with IGV were selected. Still tuning the booster pumps and dP's. Had a hiccup with controls so also still tuning optimization with condenser water, might just give up and buy a loop optimization program like Hartman's.