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Total System Efficiency
System run time is important to overall operating efficiency.
To prevent short cycling of the system, it is important to minimize
boiler on/off cycling.
Lochinvar Buffer Tanks are a cost effective way to enhance
small load effectiveness and increase heating system efficiency.
Lochinvar Buffer Tanks are also engineered as the system air
separator, further reducing the installed cost of your system,
since there is no need for an additional system air separator.
Outstanding Features:
• Increase System Efficiency - Prevent system short cycling for
greater system efficiency and longevity.
• Air Elimination System - Eliminates the need for a separate
system air separator. The unique air collection/elimination system
has a built-in air separator with automatic air vent, which reduces
system installed cost. The tank’s tangential connections create a
swirling action in the center of the unit as water enters and exits,
pushing any air held in the system to the center of the tank.
Buffer Tank
Air Eliminator
The collection tube at the tank’s center captures that air and
releases it through the air eliminator installed on top of the tank.
• ASME Construction - All models constructed in accordance with
ASME Section VIII, Div. 1 standards and labeled for 125 psi
working pressure at 400°F.
• Channel Iron Skid Mounted with Lifting Lugs -
For handling and installation ease.
• Energy Saving Performance - Jacketed tanks meet the efficiency
requirements of the latest ASHRAE Energy Efficiency Standards.
The 2” foam insulation provides low standby loss for optimum
performance and economy.
• Five Year Limited Warranty - Provides protection against tank
failure resulting from defects in materials or workmanship.
Optional Equipment:
• Temperature & Pressure Gauge
• Handhole
• Manway (300 gallon and larger models)
• Extra Tappings
• Custom Tapping & Flange Sizes
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Buffer Tank Quick-Select Chart
1. Locate the desired boiler model number from the column on the left-hand side of the page.
2. Find the “Minimum System Load” range from the three selections at the top of the chart; (0-50,000 Btu/hr)
(60,000-100,000 Btu/hr) or (110,000-200,000 Btu/hr).
3. Choose a “System T” based on the minimum temperature drop of the system (20°F/30°F/40°F).
Follow the chosen column down the chart until it crosses the row of your desired boiler. This is the suggested buffer tank necessary
to eliminate short-cycling and maintain efficiency.
Example: A CHN0991 boiler installed in a system with a minimum system load of 75,000 Btu/h and a system T of 30°F,
will need a RVU200 Buffer Tank.
0 - 50,000 Btu/HR 60,000 - 100,000 Btu/HR 110,000 - 200,000 Btu/HR
Model 20°T 30°T 40°T 20°T 30°T 40°T 20°T 30°T 40°T
COPPER-FIN
CBN0745 RVU400 RVU300 RVU200 RVU400 RVU300 RVU200 RVU300 RVU200 RVU200
CBN0986 RVU750 RVU400 RVU300 RVU500 RVU400 RVU300 RVU500 RVU300 RVU200
CBN1256 RVU750 RVU400 RVU300 RVU500 RVU400 RVU300 RVU500 RVU300 RVU200
CBN1436 RVU750 RVU400 RVU300 RVU500 RVU400 RVU300 RVU500 RVU300 RVU200
CBN1796 RVU1000 RVU750 RVU500 RVU750 RVU500 RVU400 RVU750 RVU500 RVU400
CBN2066 RVU1000 RVU750 RVU500 RVU750 RVU500 RVU400 RVU750 RVU500 RVU400
COPPER-FIN II
CHN501 RVU200 RVU200 RVU120 RVU200 RVU120 RVU120 RVU120 RVU120 –
CHN651 RVU200 RVU200 RVU120 RVU200 RVU120 RVU120 RVU120 RVU120 –
CHN751 RVU200 RVU200 RVU120 RVU200 RVU120 RVU120 RVU120 RVU120 –
CHN0991 RVU300 RVU200 RVU200 RVU300 RVU200 RVU120 RVU200 RVU120 RVU120
CHN1261 RVU300 RVU200 RVU200 RVU300 RVU200 RVU120 RVU200 RVU120 RVU120
CHN1441 RVU300 RVU200 RVU200 RVU300 RVU200 RVU120 RVU200 RVU120 RVU120
CHN1801 RVU500 RVU300 RVU200 RVU400 RVU300 RVU200 RVU300 RVU200 RVU200
CHN2071 RVU500 RVU300 RVU200 RVU400 RVU300 RVU200 RVU300 RVU200 RVU200
POWER-FIN F9
POWER-FIN B9
PBN1002 RVU1000 RVU750 RVU400 RVU1000 RVU750 RVU400 RVU750 RVU500 RVU400
PBN1302 RVU1000 RVU750 RVU750 RVU1000 RVU750 RVU750 RVU1000 RVU750 RVU500
PBN1501 RVU750 RVU500 RVU400 RVU750 RVU500 RVU400 RVU750 RVU500 RVU400
PBN1701 RVU1000 RVU750 RVU500 RVU1000 RVU750 RVU400 RVU750 RVU500 RVU400
PBN2001 RVU1000 RVU750 RVU500 RVU1000 RVU750 RVU500 RVU1000 RVU750 RVU500
F9 2:1 Turndown
B9 On/Off
POWER-FIN M9
PBN0752 RVU120 RVU120 RVU120 RVU120 – – – – –
PBN1002 RVU200 RVU120 RVU120 RVU120 RVU120 RVU120 RVU120 – –
PBN1302 RVU200 RVU200 RVU120 RVU200 RVU120 RVU120 RVU120 RVU120 RVU120
PBN1501 RVU300 RVU200 RVU120 RVU200 RVU200 RVU120 RVU200 RVU120 RVU120
PBN1701 RVU300 RVU200 RVU200 RVU300 RVU200 RVU120 RVU200 RVU120 RVU120
M9 5:1 Turndown
PBN2001 RVU400 RVU300 RVU200 RVU300 RVU200 RVU200 RVU300 RVU200 RVU120
INTELLI-FIN
IBN1700 RVU400 RVU300 RVU200 RVU400 RVU300 RVU200 RVU300 RVU200 RVU200
IBN2000 RVU500 RVU300 RVU300 RVU400 RVU300 RVU200 RVU400 RVU300 RVU200
CBN0495 RVU200 RVU200 RVU120 RVU200 RVU120 RVU120 RVU120 RVU120 –
CBN0645 RVU400 RVU300 RVU200 RVU300 RVU200 RVU200 RVU300 RVU200 RVU120
CHN401 RVU200 RVU120 RVU120 RVU120 RVU120 RVU120 RVU120 – –
PBN0502 RVU400 RVU300 RVU200 RVU400 RVU300 RVU200 RVU300 RVU200 RVU200
PBN0752 RVU750 RVU400 RVU300 RVU750 RVU400 RVU300 RVU500 RVU400 RVU300
3
34
PBN0502 RVU120 RVU120 RVU120 – – – – – –
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IBN1500 RVU400 RVU300 RVU200 RVU300 RVU200 RVU200 RVU300 RVU200 RVU120
Note: For applications outside the parameters listed above, please consult the Sizing Formula on the next page or use the
“Buffer Tank Sizing Calculator” on our website www.lochinvar.com Click on Accessories, then Buffer Tank/Air Eliminator.
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www.Lochinvar.com
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Buffer Tank Sizing Formula - Calculating Gallon Capacity
The recommended gallon capacity of Lochinvar Buffer Tanks is based on six parameters. These six parameters are used to
derive the following formula and are explained below.
Desired Run Time x (Minimum Boiler Output – Minimum System Load)
System T x 8.33 x 60
Parameters:
• Desired Run Time (Minutes) – The desired amount of sustained firing time of
each run cycle once a call for heat is detected. Lochinvar recommends a minimum
run time of 10 minutes.
• Minimum Boiler Output (Btu/h) – The output of the boiler - based on that
particular boiler’s minimum firing rate which is determined by turndown ratio
and efficiency. (For example: a PBN1501-M9 with 5:1 turndown ratio and 87%
thermal efficiency will have a “Minimum Boiler Output” of 261,000 Btu/h.)
• Minimum System Load (Btu/h) – The load, or demand, placed on the system
when the smallest possible appliance or zone has a call for heat. This value may
vary greatly depending on the application and/or building design. The Project
Design Engineer should be contacted to provide the exact value for this parameter.
• System T (°F) – The temperature drop across the system at minimum system load.
Again, this value may vary greatly depending on the application and/or building design;
therefore the Project Design Engineer should be contacted to provide the exact value
for this parameter.
• 8.33 (Pounds) – The accepted weight of one gallon of water. (Fixed value.)
• 60 (Minutes) – The number of minutes in an hour. (Fixed value.)
Once you understand these parameters and how they relate and contribute to the sizing of a buffer tank, you will have no trouble
sizing a Lochinvar buffer tank for any application or system.
Please use the following example of buffer tank sizing and selection as a guide.
Sizing Example: Calculate the Buffer Tank Gallon Capacity Using the Formula
Desired Run Time x (Minimum Boiler Output – Minimum System Load)
System T x 8.33 x 60
Use the following parameters to size a Buffer Tank:
IBN2000 (4:1 turndown and 97% thermal efficiency)
Minimum Boiler Output = 460,000 Btu/h
Minimum System Load = 100,000 Btu/h (Example only: actual System Loads may vary)
System T = 40°F (Example only: actual System T’s may vary)
From the “Parameter” explanations, we know:
Desired Run Time = 10 minutes
One gallon of water = 8.33 pounds
One Hour = 60 minutes
Using these six parameters, we can now calculate the gallon capacity of the Buffer Tank:
10 x (460,000 – 100,000) = 10 x 360,000 = 3,600,000 = 180 gallons
40 x 8.33 x 60 19,992 19,992
Based on this calculation, we would recommend an RVU200 Buffer Tank.
www.Lochinvar.com
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Buffer Tank / Air Eliminator Dimensions & Specifications
Model Gallon Supply/Return Boiler Weight
Number Capacity A B C D E F G H Connections Tappings (lbs.)
RVU120 119 59” 32” 33-1/4” 42” 30” 25-1/2” 17-1/2” 20-1/2” 3” NPT 3” NPT 500
RVU200 200 89-1/2” 32” 33-1/4” 72-1/4” 60-1/4” 25-1/2” 17-1/2” 20-1/2” 3” NPT 3” NPT 900
RVU300 318 80” 40” 42” 57-1/2” 46-1/2” 27-1/2” 19-1/2” 27-1/2” 4” FL 3” NPT 1,290
RVU400 432 80” 46” 48” 56” 44” 29” 21” 31-1/2” 4” FL 3” NPT 1,626
RVU500 504 92” 46” 48” 67” 55” 29” 21” 31-1/2” 6” FL 3” NPT 1,765
RVU750 752 104” 52” 54” 76-1/2” 64-1/2” 31” 23” 33” 6” Fl 3” NPT 2,330
RVU1000 940 128” 52” 54” 100-1/2” 88-1/2” 31” 23” 33” 6” FL 3” NPT 3,010
Notes: Custom Sizes and Configurations are Available. Consult Factory for details.
Additional Recirculation & Supply Return Connections Sizes Available. Consult Factory for details.
Typical Piping Arrangement for Buffer Tank / Air Eliminator in Boiler Systems
Lochinvar Corporation • 300 Maddox Simpson Pkwy • Lebanon, TN 37090 • 615-889-8900 / Fax: 615-547-1000
BT-03 (Reprint BT-03 4/08)
www.Lochinvar.com
3/10-Printed in U.S.A.
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