VRV/VRF versus Chilled water system 5

[sridhar1312]

Off late I have come across manufacturer after manufacturer coming out with VRV /VRF system and aggressively .It is being marketed for most of the applications.I have found the economics does not work out in favor of the VRV /VRF compared to Chilled water system.

Even in VRV/VRF digital scroll as well as VFD driven compressors are in competition. At least in the INDIAN context where predominantly only cooling is required chilled water systems are economical and reliable.
Can any one throw light and let me know the strengths and limitations of VRV/VRF system especially where only cooling is needed.
Further when we use the VRF/VRV most of the indoor units are standard product having 2 row cooling coils and does not dehumidify to the extent is neeeded for coastal climate like Madras /Bombay

 

[EnergyProfessional]

We recently installed a Mitsubishi VRF in Madison/WI. You need a backup system below freezing. Daikin/Mitsubishi rate it to -4°F... but don't recommend that. Several issues with compressor wear, low COP and freezing of coils. with a supplemental heating system you are golden.

Economics: their strength is when you have cooling/heating at the same time since it reuses that heat well. If you have mostly cooling only, or heating only... a chiller may be better. You really have to run a Trane TRACE simulation to evaluate economics. As a rule of thumb havingmany core zones, possible a server room will make a VRF economical when you need heating too.

Write and enforce really tight refrigerant leakage specifications. Refrigerant leaks are the Achilles heel. Obvioulsy a chiller is beter in that respect.

 

[RossABQ]

I was under the impression that VRV/VRF systems are getting a boost because of LEED points? While LCC analysis may be the proper engineering evaluation, precious points for Eac1 (LEED 2.2) are a different story. How do they look on a whole-system basis for purely energy costs?

 

[EnergyProfessional]

depends on case by case. You need to do an energy simulation. rule of thumb as mentioned above, have zones with likely heating and cooling at the same time. Like large core areas that need cooling when the perimeter needs heating, or server rooms. also avoids that whole reheat issue with badly designed VAV systems.

but rules of thumb don't get you LEED points

I think LEED 3.0 requires energy simulations. However, only two can simulate VRF systems. Trane TRACE is really good and also a design tool. EnergyPro is based on the DoE 2.1 engine from the stone ages. that really is not a good tool. You migth as well use the (free) eQuest. A Daikin salesman once recommended EnergyPro. then I bought TRACE because of all the chiller, boiler, ventialtion details it can calcualte. He then told me I made a mistake. Soem months later I met him again and he told me they (not sure if just his office, Or DAIKIN) tested it and found it not suitable for VRF. This tells me much about salesman recommendations and EnergyPRo. DoE does not have the VRF capability and will never have since it is not that detailed.

I'm digressing.. but you should consider a good software. Like with all HVAC, there is no perfect system that fits all.

 

[marcoh]

I've installed quite a few VRF systems and many more chilled water systems and you need to consider each application on it merits.

- VRF is cheaper.
- VRF is more energy efficient than air cooled chiller plant.
- VRF is less efficient than water cooled chiller plant.
- VRF is 'plug and play' and simple to install
- VRF controls are simple and don't need to be programmed as per BMS systems.
- VRF FCU are limited to standard selection. Will required outside air preconditioning for high humidity/high outside air quantities.
- Check warranties if using VRF for 24/7 computer rooms. Daikin warranty is void if used for computer rooms!
- VRF systems are limited to the whomever supplied the original system. What happens if you need to replace a FCU in 10 years time? Not an issue with chilled water.
- VRF systems probably won't last as long as chilled water systems.

Generally I would say if an air cooled chiller is proposed, then a VRF system is probably a suitable alternative, especially for office applications (and using outside air preconditioning.

 

[Waramanga]

My experience with the vrv systems is positive with two major drawbacks. Much shorter lifespan than chilled/hot water (high churn buildings only) and the temperature control at low load conditions is poor. Proper heat load calcs are a necessity (no over-sizing), condition OA before the FCU and even then expect some complaints in the in-between seasons.

 

[dbarry14]

I have designed several VRF systems, typically I use Sanyo or Mitsubishi. Everyone needs to remember there are heat pump (heating or cooling) and heat recovery (heating, cooling, or simultaneous) VRF systems. Also each mfg does things differenty. Sanyo will cool down to 14F. It will provide cooling lower if in simultaneous heating/cooling mode. The energy savings are enormous on VRF systems compared to chilled water, running one inverter driven compressor vs. a chiller and chilled water pumps. You also save a lot of space w/a VRF system. Plus VRF systems are QUIET! A VRF compressor vs. a chiller isn't even a comparison. It's like a whisper compared to a football game. Outside air does need to be treated independently of the VRF system. ERVs help reduce load additionally (if you can use them). VRF isn't the end all be all, but they do have their place if they are applied properly.

 

[mauricestoker]

Ended up deciding on a mix.
VRF where space is available in condenser room, rooftop chillers for separate short stack runs occur.
Now just have to have asbestos surveys.

 

[dalet57]

I am inquiring about a VRF system, we have been told about it's efficencies by our HVAC company. Anyone with any sucess with these types of units. 50 unit apartment building in a midwestern climate.

 

[AnotherEllis]

I have several of my VRV and VRF designs installed and up and running here in my hot/humid climate. I've had nothing but good experiences so far. As far as VRF vs. Chilled Water, the individual project merits will determine the appropriate solution.

I have one 400 ton install that was originally designed as a small chilled water plant, but during schematic design the VRF beat it out on first cost. That install was an anomaly, and in other designs in this tonnage range the chilled water killed the VRF in LCC.

As for efficiency, yes a well designed chiller plant will generally beat out a VRF system, but the chilled water app falls on its face under 100 tons. The VRF does great in this range.

Also, I have a LEED v.2 for Schools project right now that I managed to hit 8 points on EA Credit 1 using DOAS with energy recovery wheels and Daikin VRV with oversized condensing units. This was about 60 tons total (small private school). Try that with chilled water at that tonnage!

 

[ChrisConley]

What did you use to model the VRV system for LEED?

 

[AnotherEllis]

On this one, EnergyGauge.

And I need to make a correction: I got 6 points on that project, not 8. Using a similar design on a renovation I anticipate 8 as per the model, but it has not yet been audited and accepted by the reviewers. Both projects had savings vs. the baseline model within 1% of each other, but the renovation scale gives more points.

On the renovation we are using Carrier's H.A.P. Both projects are v.2; they kicked off some time back then went on hiatus, but we registered both under the old rating system as the fundamental designs were set up to take advantage of the older point structure.

 

[tscna88]

Personally I can tell you I was impressed with the Daikin VRF system we were involved with. Ours was a heat recovery not heat pump and good down to -4F in heating. We are in Ohio and it was down to below zero last year and we were able to keep the building at 72. I did add a makeup air unit with heat for fresh air and it supplemented on cold days, but it is only a 2000 cfm unit. We purposely over sized the units for the heating cycle and because of the VFD on the compressors and the Condenser fans, capacity control for over sizing didn't affect us in cooling mode. As far as controls we are a control contractor and put a bacnet card in and can control as well as monitor. Also, benefits over the four pipe were redundancy by zones. We had 80 units served by 4 20 ton condenser units. We had one go down and the other parts of the building still were being maintained. The energy savings has been better than they had with the original chiller/fan-coil application.

 

[DavidNJ]

- VRF is cheaper.
- VRF is more energy efficient than air cooled chiller plant.
- VRF is less efficient than water cooled chiller plant.

Since some chillers are VRV, how are the direct VRV to air systems more efficient?

If forced air is used for heating, how do you integrate with a distributed VRV system? Don't they require their own proprietary air handlers without economizers, reheat, etc.?

 

[acedrew]

@tscna88 Hi, I'm a controls guy myself and I want to do something very similar using the BACnet gateway. Could you give some more details on how that worked for you guys? Ideally, I would like to tell the system which aircoils to run and in what mode through the gateway. Can I do away with their zone controllers that way?

Andrew

 

[mauricestoker]

As an added twist, has anyone used a water source heat pump with VRF?

For a job I'm working on, there are twenty single story masonry construction buildings, with failed, 67-year old steam distribution loop from off central plant, and a production well nearby, idled for the last 12 years for plume modeling. I was thinking about a WSHP condenser loop to go along with VRF. Other option would be similar to Colt industries, water and refrigerant flow, but not too many American vendors or installs.

 

[acedrew]

@mauricestoker:

We just priced out a Daikin system with water source condensers, 72 Ton was $302K. The largest water source condenser they make is 12T.

Our current belief is if you're going to use WSHP, just use WSHP. The VRF guys don't really have any benefit over WHSP, because there's heat recovery built into the WHSP. VRF seems to be a great option if the alternative is DX. WSHP with zone pumps and demand based control can easily match efficiencies, I believe, with a much less complex control and distribution.


Andrew

 

[DavidNJ]

A VRF can be more efficient regardless of how the condenser is cooled. The oversized condenser and heat exchanger helps; and there are fewer losses between cycles. Obviously a staged system does some of this itself.

For the delivery side, water capacitance and possible storage would mask any advantage.

 

[MrFreeze42]

I agree with DavidNJ, a VRF system is can be more efficient regardless of cooling, and in some cases far more efficient.

http://www.hvacknoxville.org

Repair Services.

 

[Drazen]

sridhar1312, I am curious how do you design central chiller on 60-80% of total peak capacity?

As one of main VRF advantages I allways considered expansion valves on each indoor unit (or connection box related to unit), which allows capacity modulating for each and every room.

In chilled systems you have on-off valves in vast majority of cases. Modulating can be achieved by zone valves for some partiuclar zones consisting of number of rooms.

That forces you to find coincidental summary of zone peaks to size chiller. In VRF you are finding coincidental summary of each room peaks, which can give you sensibly smaller size, depending on building geometry and distribution of room orientations.

The other advantage is on end-user level - on-off cycling in rooms is allways less comfortable than modulating.

In some restoration systems I designed literally cascades of pipe runs, which would not be possible with water pipes as air would be trapped everywhere.

Now, safety norm is introduced in my country officially, there is EU standard that is actually based on Japanese standard which gives exact, officially allowed refrigerant charge based of minimal room volume, applied only for rooms where sleeping can occur.

That limits these systems for many residential and hotel applications; other than that I find mostly advantages of VRF/VRV lately.

 

[cry22]

Sorry folks but I am kind of disapointed by most of the posts in this thread, a lot of mentions of cheaper and more efficiency without much scientific evidence offered, no serious LCC performed (such as considering replacement costs, proprietary controls, etc). Goes to show you that this VRF is applied somewhat blindly.

Also disapointing is that these kinds of answers (VRF Vs CHW) ought be found in ASHRAE, but out "dear for-progit ASHRAE" does not like to put its money where its mouth is. At least volunteer an opinion.

No one mentionned tonnage application for this sytem, is this system applied to 100-plus tons? or are we talking about 40-80-ton kind of load.

I also do not see anyone considered modular air cooled chillers Vs VRF (at Part load, chillers are OFF, and nothing beats OFF). My take is that modular air-cooled offers a lot less headaches and it compares fairly well, so why go with an experimental system?