HVAC

HVAC Questions

  1. When investigating the replacement of an HVAC system, what is a reputable source for general estimates on efficiency gains from new systems?
  2. I've identified the make and model number for various old motors that are on our facilities, and I want to figure out how out-of-date and inefficient they are, and whether they would be worth replacing. Does anyone have any insight into this discovery process? I intend to call the manufacturer, but am a bit unsure of how to ask "how inefficient is XYZ motor that you made in 1945?"
  3. Has anyone tried to calculate the savings through VFD installation? I have a "VFD savings calculator" which was given to me by the HVAC company and provides only $$ savings. I want to get at the information another way, if possible, to double check the estimated savings. The challenge is that it is hard to predict how the motor's load will be reduced in the future.
  4. I am investigating thermal energy storage tanks that can store chilled water / ice during the night and use that in place of a chiller. Does anyone have any expertise in these? I need to know how much it costs to set up such tanks and how beneficial are they? Any pro's and cons?

HVAC Answers

1. Q: When investigating the replacement of an HVAC system, what is a reputable source for general estimates on efficiency gains from new systems?

A: The Department of Energy (DOE) has an online tool that allows users to input basic information about an existing chiller and a potential new chiller. It will then return a few different scenarios for annual cost savings. You need to know the KW/tons efficiency. DOE also gives some guidelines about what efficiency level to replace with.

Visit the following website for their tool. They have different options for different systems: [ http://www1.eere.energy.gov/calculators/buildings.html]

Another source (a climate corps company’s energy audit team) recommended using the following equation when calculating the annual kWh usage of chillers (which can help you estimate what your current unit is using, and what the unit you're considering will use).

1. Determine the kW of the chiller.

  • For a three-phase motor, use the equation below:
        • kW = Amps x Volts x Phases x Load Factor x 1.73 x 0.85 / 1000
  • Amps, Volts, and Phases can be found on a small metal plate on the unit.
  • Load Factor is usually 0.85 (85%) for motors.

2. Get the annual kWh used by the chiller:

  • kWh = kW x duty factor x hours of operation per year

Duty factor: For most chillers that are properly loaded, a duty factor of 0.3 is appropriate to use. In our case, one machine is on 24x7 so we gave it a duty factor of 0.5. We have another machine that is rarely used, which was assigned a duty factor of 0.1.

Note: .85 should be in their twice - once for the load factor, and once as just a constant you use. The 1.73 is another constant. I'm not sure exactly what each does, but they were given to me by our energy experts.

2. Q:I've identified the make and model number for various old motors that are on our facilities, and I want to figure out how out-of-date and inefficient they are, and whether they would be worth replacing. Does anyone have any insight into this discovery process? I intend to call the manufacturer, but am a bit unsure of how to ask "how inefficient is XYZ motor that you made in 1945?"

A: An excellent resource for investigating fixed speed fans is on Yaskawa's (a VFD manufacturer) website. It does a good job of comparing fixed speed and VFD performance.

We ran a test on our equipment here using our Building Automation System. Running the pneumatic fan veins at different % openings, we captured amperage that we could compare against the one VFD unit we already have in place. If all of your fans are old, I think the online resources will be of help in comparing how your motors/fans work versus VFDs.

Note that pneumatic is outdated technology and they may not have available replacement parts.

3. Q:Has anyone tried to calculate the savings through VFD installation? I have a "VFD savings calculator" which was given to me by the HVAC company and provides only $$ savings. I want to get at the information another way, if possible, to double check the estimated savings. The challenge is that it is hard to predict how the motor's load will be reduced in the future.

A: Try using the Energy Savings Predictor by Yaskawa. It evalueates energy savings as well as cost savings.

Another good tool could be a software called SINASAVE and it can be downloaded free from their website. It should be a good basic calculator to tell you how much you would save by putting VFD's on your motors or replacing the motors completely.

4. Q:I am investigating thermal energy storage tanks that can store chilled water / ice during the night and use that in place of a chiller. Does anyone have any expertise in these? I need to know how much it costs to set up such tanks and how beneficial are they? Any pro's and cons?

A: According to experts from Rocky Mountain Institute:

Thermal (ice/liquid, cold or heat) storage is on the whole a good thing because it reduces load on the utility grid. Folks consider it an efficiency measure, but it is more precisely considered as a load displacement strategy (like solar hot water), and can also be used as a demand response strategy. The biggest advantage to a thermal ice storage system is in shifting the demand for electricity to off-peak times, therefore avoiding peak electricity demand charges (if they apply).

As such, it is most applicable for customers who have access to time of use rates in order to take advantage of their ability to shift load off peak times. For customers without time of use rates, there may be a very slight advantage for energy conservation due to the chiller operating when the outside air temps are cooler at night but this is pretty small.

A more advanced concept being discussed now is to couple thermal storage with solar PV. This is because solar energy has a relatively short peak, and commercial facilities may experience peak cooling needs after the solar energy begins to decline by around 2pm. Ice/cool storage can be kicked on at this point in order to fully shift load away from a long peak period.

Commissioning is a very important issue with ice storage, particularly in retrofit situations. This is because the OLD a/c unit often has lost its calibration against the actual needs of the occupants, and when the new thermal storage unit is installed, this often exposes underlying issues with existing units. The new thermal storage unit instead is blamed. Sometimes additional tuning or even new parts and repairs are needed to the old unit so that the thermal storage retrofit can work properly.

For costs related to these systems, a good contact would be Robert Willis at Ice Energy (contact info below). They make the Ice Bear system installed at the RMI office. Their biggest market right now is in California. The utilities are paying to install these because it is cheaper to offset the energy usage to night time rather than build more power plants.

Robert Willis
Senior Development Engineer
Ice Energy, Inc.
9351 Eastman Park Dr.
Suite B
Windsor, CO 80550
moc.ygrene-eci|silliwr#moc.ygrene-eci|silliwr

E Source has a lot of papers and articles written about thermal storage technologies, and there are a number of online green building blogs and magazines that provide some useful information as well, such as buildinggreen.com

Resources

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