Added Conversion Tables to Blog

I've added a bunch of conversion tables like the one below to the blog.

They are all located right here.

POWER CONVERSIONS

From:	To:
watt [W]kilowatt [kW]horsepower [hp]horsepower (boiler)horsepower (electric)horsepower (water)Btu (th)/hourMBHton (refrigeration)volt ampere [V*A]	watt [W]kilowatt [kW]horsepower [hp]horsepower (boiler)horsepower (electric)horsepower (water)Btu (th)/hourMBHton (refrigeration)volt ampere [V*A]
Result:
power conversion factors provided by unitconversion.org

FREE Psychrometric Software

If you like the charts that I created to show psychrometric processes (like here), you're in luck.

Johnson-Barrow has made a deal to make this software available to our customers. We've also made some major aesthetic changes that we feel are a huge improvement: We've changed the chart colors and added a dynamic new logo!:




Pretty spiffy, huh?

The free version of the software allows you to do some simple analysis and process charting--allowing you to create high quality psychrometric charts for presentations or personal use. Additionally, a copy of the free version gives you a sizable discount off of the full version that is available here (chose HDpsychchart Pro Edition OEM upgrade SKU# HD1001, select Johnson-Barrow as OEM company).

The full version allows you to do the following:

• Model mixing, direct evaporative and humidification processes
• Create charts at any elevation
• Add climactic bin data
• Create flow charts
  
• Create detailed psychrometic process data points tables
• Vary the limits and extents of the chart axes
• Show ASHRAE winter and Summer comfort zones
• Project constant condition lines for ease of analysis

And many more tasks that make psychrometric chart analysis easy. The software also comes with additional tools like fan law calculators and even a loan payment calculator!

The free software is available for direct download on the toolbar to the right, on our www.jbarrow.com main page or right here.

UPDATE:

Some users have reported a problem with the software that prevents proper registration of the file. A new file that does not have this problem will shortly be uploaded.

HVAC System Efficiency Tool

Designers and owners are continually bombarded by claims of equipment efficiencies. Industry groups such as ARI, AMCA or CTI have been set up to validate these equipment efficiencies to give these claims credence.

However, it isn't the equipment efficiency that drives the energy use of the building, but the overall efficiency of the system that the equipment is part of.

Steve Kavanaugh, University of Alabama Professor, ASHRAE fellow and author of the ASHRAE design guide for ground-loop heat pump systems (with Rafferty) stresses the importance of the system efficiency. He has also provided (free of charge) a handy tool to calculate the system efficiency of typical HVAC systems, given the efficiencies of their component equipment.



This tool (HVACSysEff06)is available at Steve's Geokiss website software download page.

Take a look around--there are some other interesting tools there, too.

Introduction to Indirect-Direct Evaporative Cooling

Now that we have covered the basics of the indirect and direct evaporative cooling processes, it's time to consider one more wrinkle--putting them together.

In the IDEC cooling discussion, I made the point that not only do we get a reduction in dry-bulb temperature as our airflow passes through the IDEC unit, but we get a reduction in wet-bulb temperature, also. And since we now have seen that the direct evaporative cooling process depends critically on the wet-bulb temperature of the air it is cooling, it seems we should get some advantage by running the air through the IDEC section, and then running it through the direct section. And we do:

(click for larger image)

As you can see, the resultant leaving dry bulb is on the order of 64º, which is better than the resultant of 72º from the indirect section alone, or 69º for the direct evaporative section alone. Now 64º degrees may not seem cool enough for typical cooling applications--and for most projects it probably isn't (although it is important to not that ASHRAE comfort conditions can be met with this leaving air condition in a predominantly sensible load application given enough air). But keep in mind that this is the performance on a design day. How many hours a year would you be able to meet the traditional supply air temperature of 55º? Lets look at psychrometric chart with Seattle bin data loaded into it:

(click for larger image)

A quick note of explanation: The vertical line at 55º is the economizer line--any climactic conditions to the left of that line can be used to create cooling air directly using OA alone (or mixing OA with RA) and thus require no additional cooling at all. The blue diagonal line along the 53º wet-bulb line is a conservative mapping of the direct evaporative regime. At any bin hours under this line, direct evaporative cooling can be applied to the ambient OA to achieve cooling air directly. And lastly, the red diagonal line above that is the indirect-direct evaporative cooling regime, where the application of both cooling techniques will provide acceptable supply air conditions (assuming about 70% effectiveness on the IDEC). And above that line, the indirect evaporative system can still be applied to greatly reduce the load on any supplemental mechanical cooling system, if used to meet the same 55º leaving air condition.

Two things jump out of this analysis: First, the vast majority of the hours are satisfied without using mechanical cooling. In fact, in Seattle, most hours are met with simple economizers--which explains the emphasis in our local codes on this cooling technology. You can even think of evaporative cooling as simply an enhancement to the standard economizer. The second takeaway is that there are still quite a few hours that are not met. How can we address this?

Well, one way is to play around with the leaving air temperature. If we supply some more air to the zone, we can provide warmer cooling air. Let's look at that same chart, only this time lets use a supply air temperature of 60º:

(click for larger image)

By simply providing for a little more air to the zone, we meet a much higher percentage of the bin hours; so much so you that can now consider a system without mechanical cooling, as long as the occupants are willing to accept a few more hours outside of standard comfort conditions a year. Granted, this additional comfort comes at an energy cost--the cost of moving that additional quantity of air. This cost is, of course, offset by the avoidance of mechanical cooling. But, additionally, we know from the previous chart that this additional air is not needed all of the time. A variable speed control on the fans would naturally bring the air volumes down during periods where colder air is achievable.

One of the things that should be obvious is that this analysis is greatly dependent on the local climate and elevation of the project. To evaluate how effective this cooling method is, you need to create similar plots for each project locale. And where you are in the state has a great effect on how well you do. For example, a cool-wet climate like that on the Olympic Peninsula sounds like it might be a good candidate. So let's see how it compares to Seattle:

(click for larger image)

It looks pretty similar to Seattle, as we might guess. How about a hot, dry climate like Spokane?:

(click for larger image)

That's a real winner! There's only a small fringe of hours outside of the range where indirect/direct evap works alone. So if Spokane works, surely Yakima must also be a great candidate:

(click for larger image)

Hmmm... There's quite a few hours outside of the indirect/direct evap zone. Good thing we did this analysis before committing to a evaporative-only system!

Indirect-direct evaporative cooling, either as the main cooling technology or as an enhancement to the economizer cycle is a technology that has wide application in the Pacific Northwest, even in rainy Seattle. But it is a technology that requires careful analysis--it's not as simple as throwing compressor tons at a cooling problem. With today's emphasis on energy efficiency and sustainability, it is a technology that deserves a second look.

There is certainly more to talk about on the subject. Future topics will include integrating compressorized cooling with an evaporative system, indoor comfort conditions, water treatment and maintenance, control of evaporative systems. and the role of return air in these systems.

Resources you may find useful:

Energy Labs Indirect/Direct System Performance Calculator (Simply the direct and indirect calculators linked together
Energy Labs Direct/Indirect Evaporative Systems Engineering Guide (booklet format)

Introduction to Direct Evaporative Cooling

Now that we have discussed Indirect evaporative cooling, let's move on to the next question: What is direct evaporative cooling?

Direct Evaporative Cooling is a process where air is sensibly cooled by the effect of the evaporation of water directly into the delivered air stream. This is typically accomplished by use of a wetted absorbent media in the air stream, most commonly Munters CelDek (pdf) or GlasDek (pdf).

Evaporative media in an Energy Labs Unit

This process has the advantage over IDEC systems in being much more efficient (with efficiencies in the range of 90% easily attainable), but with one major difference: Direct Evaporative cooling is an adiabatic process. This means that there is no energy added to or removed from the airstream. The enthalpy of the air is unchanged, even as the sensible temperature is cooled.

How is this possible? Well, essentially you trade sensible heat for latent heat. As you reduce the dry-bulb temperature of the air, you concurrently increase the humidity ratio of the air. What you lose in sensible heat, you make up in the heat embodied in the evaporative phase-change of the water.

What does this look like on a psychrometric chart? Take that Seattle design day* of 85º/67º db/wb. Let's bring in 22,000 CFM of 100% OA. If we select a direct evaporative system with an 89% efficiency, the leaving air temperature will be about 69º/67º. Note that the wet bulb is essentially unchanged. The chart of this process is below:

(click for larger image)

Essentially, for this service, you get about 32 tons of sensible cooling but and zero tons of total cooling. If you were to allow this supply air to warm sensibly to a room temperature of 75º, you would find that the space RH would be close to 70%, which would probably not be acceptable for standard comfort cooling applications. However, in high-sensible cooling applications, like, say, data centers, this method of cooling has great application.

Additionally, since the resultant indoor conditions depend greatly on the outdoor air conditions, Direct evaporative cooling can provide acceptable air conditions for much of the year in a cool, dry climate like Seattle. In fact, any time the ambient wet bulb temperature is 53º or less, the direct evaporative cooling can provide supply air almost identical to that off of a 55º cooling coil, with pressure drops at the media on the order of half that of a standard cooling coil! Direct evaporative cooling can used to essentially greatly extend the hours of economizer performance available on almost any cooling system.

But the benefits do not end there--because pre-cooling with direct evap systems upstream of a cooling coil can significantly decrease energy costs for sufficiently dry ambient conditions:



Resources you may find useful:
Energy Labs direct evaporative performance calculator
Energy Labs Direct/Indirect Evaporative Systems Engineering Guide (booklet format)


*Note: When applying evaporative systems, often it is necessary to consider the performance of the system at the ASHRAE evaporative design day conditions, in addition to the sensible design day conditions that we commonly use. And, additionally, it can use what would normally be unwanted space heat in the return air to provide beneficial humidification in times of low humidity.

Introduction to Indirect Evaporative Cooling

What is indirect evaporative cooling?

Indirect Evaporative Cooling (IDEC) is a process where air is sensibly cooled by the effect of the evaporation of water across a heat exchanger. The advantage being that for most climactic conditions, there is a significant difference between the wet-bulb and the dry bulb temperatures at design conditions. This 'wet-bulb depression' allows the designer using indirect evaporative cooling to create supply air temperatures below the ambient dry-bulb temperature without using any refrigeration at all.

Take a Seattle design day of 85º/67º db/wb. If we bring in 100% OA (which is pretty common for IDEC systems) we will have, obviously, an OA condition of 85º/67º. If we have indoor air to exhaust and use as a heat sink in a traditional, dry air-to-air heat exchanger, we will have about 75º air to use to cool down the 85º OA. Assuming about a 70% efficiency for this type of heat exchanger, that means we can realistically drop the OA by about 70% of the difference from 85º to 75º or about 7 degrees. We should be able to get a resulting LAT from the HX of 78º. Note, however, that we will need some sort of refrigeration in our system to create the indoor environment of 75º from which we are taking conditioned air to cool the OA.

Now let's consider an IDEC system for the same service. This sort of system can take on many forms, including the exact same configuration as noted above, simply with the addition of a direct-evaporative media section in the exhaust air upstream of the air-to-air heat exchanger above. For this comparison, however, let's use a built-up Energy Labs IDEC system. This is essentially a closed-loop fluid cooler for air. An induced draft fan pulls OA upwards past water spray to encourage evaporation and the supply air is cooled across an internal heat exchanger without contacting the water.

Energy Labs IDEC Module

To make this realistic, let's give this service an actual CFM and pick a particular IDEC model. Let's say this is a 22K cfm service and let's pick the nominal I-220-48 IDEC unit. With 85º/67º OA conditions*, the effective temperature difference across the heat exchanger is not 10º (OA db of 85º-EA db of 75º) but actually 18º (OA db of 85º - OA WB of 67º). Note we did two things, we increased the overall temperature difference the heat exchanger sees, and we eliminated the need to have an available exhaust air stream exhausting pre-cooled air. Checking the performance of this particular IDEC unit, we see that it has an overall effectiveness of 69% at these conditions, and the LAT from this system is 72.5º/63.2. That's a 5.5 degree improvement in LAT, or, for this supply air quantity, nearly 11 additional tons of cooling. And we don't need to have any mechanical cooling anywhere in the building to achieve this leaving air condition.

Let's examine this cooling effect on a psychrometric chart:

(click for large image)

The first thing you should notice is that the cooling process is purely sensible--no humidification or dehumidification is performed. The other thing you should note is that the supply air wet bulb temperature is a few degrees cooler than the OA wet bulb temperature, 63º vs. 67º. This is of critical importance when applying direct evaporative cooling to these systems in an indirect/direct hybrid system.

In the end, however, you can see that about 25 tons of cooling was provided, at a mechanical cost of about 1" of static pressure drop and the operation of 3 3/4 HP of fan and pump energy for the IDEC unit.

This is very inexpensive and sustainable cooling. Of course, the delivery temperature is higher than typical for standard air-conditioning applications, but if viewed as a first stage of a multi-stage system, you can see that there is a compelling case to be made for using this sort of technology to at least partially offset cooling loads that would traditionally require compressorized cooling, and greatly expand the hours of available economizer function.

Resources you may find useful:
Energy Labs IDEC performance calculator
Energy Labs Direct/Indirect Evaporative Systems Engineering Guide (booklet format)

*Note: When applying evaporative systems, often it is necessary to consider the performance of the system at the ASHRAE evaporative design day conditions, in addition to the sensible design day conditions that we commonly use.

Why You Can't Buy an NC 35 Air Handler

No, it's not because we can't make quiet air handlers.

It's because NC isn't the right criteria to use to specify an air handler's sound level.

Why not? Well, to understand that, we have to discuss what NC is, exactly.

NC levels are defined by a series of curves that define the maximum sound level at a given frequency that an ambient sound can exhibit. Stated like this, it seems simple in the extreme to apply this rating to the sound level created by an air handler--but there is one important point missing: NC is a property of spaces, not equipment. Typically, allowable NC values are determined from charts like these:

It doesn't matter if the air handler whispers or is a screamer--if the sound levels in the space are below an acceptable NC curve, the sound level is acceptable. But this resultant sound level depends on a myriad of factors--the discharge sound level from the air handler, the duct layout, the selection of diffusers, attenuation devices, and, importantly, the room itself.

Hard surfaces and small volumes will tend to result in louder overall conditions, while large volumes and soft surfaces quiet a space. And, of course, sound generated in the space or from outdoor sources (traffic, etc.) will affect the overall NC level of a space.

How can you account for these effects? Well IAC has created a simple worksheet to determine the required insertion loss criteria needed in an attenuator array to meet a given target NC level. The SNAP sheet (Systemic Noise Analysis Procedure) is a simple method of calculating the resultant sound levels due to the HVAC system in a space. We've created a simple spreadsheet that helps keep the calculations straight here. Just simply copy the NC level you wish to meet from the green-tinted table at the bottom and paste those cells into the green bar at the top of the sheet. Then enter the discharge sound level from the air handler in the blue cells. If you follow the step-by step instructions on the SNAP form, you should be able to fill out the yellow cells with the sound attenuating characteristics of the system you are designing.

What you will have after putting in all this data is a required insertion loss criteria that should help you select a sound attenuator. Once you have picked one, just input its insertion loss performance into the first red bar, and the self-noise criteria in the next two bars. A successful selection will give you a sound attenuator that brings the sound level below the NC curve you are trying to hit, and does not generate enough self-noise to bring the sound levels back up above it!

This procedure only accounts for sound generated and transmitted by the HVAC system serving the space--You will need to account for other noise sources separately. But at least it takes care of the noise source you as an HVAC designer/contractor control!

How should you specify your air handler sound performance? By specifying the outlet, inlet and radiated sound power levels. As long as you have verified that the appropriate NC level in the space will not be exceeded with the specified values, you can be assured that any air handler meeting or beating your specification will be an appropriate fit.

HVAC Engineering Calculations Software

Engineering Power Tools is a third party shareware program that some of us at Johnson-Barrow have found useful. It is an engineering program with an HVAC module that includes the following HVAC modules:

☆ Air Flow Thru Perforated Plate
☆ Blower Wheels
☆ Clean Room Standards**
☆ Control Valve Sizing**
☆ Convection Coefficients
☆ Duct Sizing**
☆ Fan Law Calculations
☆ Fluid Flow in Pipes
☆ Heat Index**
☆ Heat Loss From Insulated Pipes**
☆ Inert Gas Purge Rate**
☆ Orifice Flow
☆ Pipe Sizing Tables

• Air
• Natural Gas
• Water

☆ Pressure & B.P. vs. Altitude**
☆ Properties of Air
☆ Psychrometrics
☆ Psychrometrics II**
☆ Refrigerant Vapor Pressure**
☆ Safety Ventilation
☆ Saturation Tables
☆ Solar Radiation
☆ Standard Atmosphere Data

• Calculations**
• Table (SI Units)**
• Table (US Units)**

☆ Steam Pipe Sizing
☆ Temperature Conversions
☆ Water Hammer**
☆ Wind Chill Factor**

**Available in "Plus" version

If it looks useful to you, you can try before you buy.

Pressure Conversions

From:	To:
pascal [Pa]kilopascal [kPa]newton/sq. meterbarpound-force/sq. footpound-force/sq. inchpsi [psi]cm mercury (0°C)inch mercury (32°F)inch mercury (60°F)cm water (4°C)inch water (4°C)foot water (4°C)inch water (60°F)foot water (60°F)	pascal [Pa]kilopascal [kPa]newton/sq. meterbarpound-force/sq. footpound-force/sq. inchpsi [psi]cm mercury (0°C)inch mercury (32°F)inch mercury (60°F)cm water (4°C)inch water (4°C)foot water (4°C)inch water (60°F)foot water (60°F)
Result:
© unitconversion.org

Area Conversions

From:	To:
square meter [m^2]square kilometersquare centimetersquare millimetersquare mile [mi^2]square foot [ft^2]square inch [in^2]acre [ac]	square meter [m^2]square kilometersquare centimetersquare millimetersquare mile [mi^2]square foot [ft^2]square inch [in^2]acre [ac]
Result:
area conversion factors provided by unitconversion.org

Length Conversions

From:	To:
meter [m]kilometer [km]centimeter [cm]millimeter [mm]micron [µ]mile [mi, mi(Int)]foot [ft]inch [in]mil [mil, thou]angstrom [A]	meter [m]kilometer [km]centimeter [cm]millimeter [mm]micron [µ]mile [mi, mi(Int)]foot [ft]inch [in]mil [mil, thou]angstrom [A]
Result:
length conversion factors provided by unitconversion.org

Velocity Conversions

From:	To:
meter/second [m/s]meter/minute [m/min]kilometer/hour [km/h]foot/minute [ft/min]foot/second [ft/s]mile/hour [mi/h]Mach (20°C, 1 atm)Mach (SI standard)	meter/second [m/s]meter/minute [m/min]kilometer/hour [km/h]foot/minute [ft/min]foot/second [ft/s]mile/hour [mi/h]Mach (20°C, 1 atm)Mach (SI standard)
Result:
© unitconversion.org

Energy Conversions

From:	To:
kilowatt-hour [kW*h]horsepower hourBtu (IT) [Btu (IT)]Btu (th) [Btu (th)]thermtherm (US)	kilowatt-hour [kW*h]horsepower hourBtu (IT) [Btu (IT)]Btu (th) [Btu (th)]thermtherm (US)
Result:
© unitconversion.org

Volume Conversions

From:	To:
cubic meter [m^3]cubic kilometercubic centimetercubic millimeterliter [L, l]milliliter [mL]barrel (oil) [bbl (oil)]barrel (US) [bbl (US)]gallon (US) [gal (US)]cubic yard [yd^3]cubic foot [ft^3]cubic inch [in^3]ccfacre-foot [ac*ft]	cubic meter [m^3]cubic kilometercubic centimetercubic millimeterliter [L, l]milliliter [mL]barrel (oil) [bbl (oil)]barrel (US) [bbl (US)]gallon (US) [gal (US)]cubic yard [yd^3]cubic foot [ft^3]cubic inch [in^3]ccfacre-foot [ac*ft]
Result:
© unitconversion.org

Power Conversions

From:	To:
watt [W]kilowatt [kW]horsepower [hp]horsepower (boiler)horsepower (electric)horsepower (water)Btu (th)/hourMBHton (refrigeration)volt ampere [V*A]	watt [W]kilowatt [kW]horsepower [hp]horsepower (boiler)horsepower (electric)horsepower (water)Btu (th)/hourMBHton (refrigeration)volt ampere [V*A]
Result:
power conversion factors provided by unitconversion.org