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Fulton Systems - Frequently Asked Questions

Click on the drop down links below to read a frequently asked question:

Find some brief answers below to frequently asked questions about Fulton products and heat transfer equipment.

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General Application Questions

How do I calculate payback?

Payback calculations can be performed by evaluating the savings associated with a boiler system upgrade (incorporating the thermal efficiency gains, radiant heat loss decreasing, and electrical consumption decreasing). A payback calculation can show how long new equipment will take to pay for itself, meaning the money that would have been used to operate an old system would be used toward the cost of purchasing a new system. Simple payback is calculated as the cost of installation / yearly savings.

What is a fire tube boiler?

Any boiler where the products of combustion flow on the inside of a tube with the heat transfer media (ex. water, steam, or hot oil) on the outside. The tubes can be orientated vertically (i.e. Fulton VMP, J Series), horizontally (i.e. Fulton FBS, RBC).

What is a water tube boiler?

Any boiler where the products of combustion flow on the outside of a tube with the heat transfer media on the inside (i.e. Fulton FT-C).

What is the turndown of a boiler?

Turndown is the ratio of a boiler’s minimum fuel input as compared to its maximum fuel input. For example, a boiler with a maximum fuel input of 585 kW/hr and a minimum fuel input of 117 kW/hr would have turndown ratio of 5:1 (585 divided by 117 is 5).

What is modulation?

Modulation is the ability of a boiler to adjust its firing rate based off of the temperature setpoint the boiler is trying to achieve. Fulton boilers can be built in a number of electrical configurations to accomplish modulation by operating off the controls on the boiler itself or receiving a signal from a control system or building management system. For example, a Fulton boiler with a maximum fuel input of 585 kW/hr, would be set up to operate and any input between 117 kW/hr and 585 kW/hr.

What is a thermal fluid system?

A thermal fluid system is a closed loop using mineral or synthetic oil as the heat transfer fluid. These systems operate at elevated temperatures while maintaining low system pressures. Fluid is circulated within the heater tubes and flue gases heat the fluid.

When should I use a thermal fluid system?

The choice between a steam system or a thermal fluid system is governed by the process requirements. The range or process temperature is a deciding factor. If the system’s required temperature is above the freezing point of water (0°C) and below approximately 180°C, the choice is usually steam. However, if the required temperature is below 0°C or above 180°C, thermal fluid may be a better solution. Thermal fluid heater systems can be designed with maximum operating temperatures to 360°C.

Steam Systems

When should I use high-pressure versus low-pressure steam?

The pressure of the steam is directly related to its temperature. So process temperature will require steam used to be at a specified pressure. For example, a process requirement that needs temperatures at 150°C will require steam delivered at 3.8 barg or higher.

Hot Water Systems

Why do boilers have a minimum flow requirement?

Boilers with low water volumes require a minimum flow requirement to prevent localised boiling and subsequent heat exchanger damage in a low to zero water flow situation. Minimum flow requirement varies by boiler design. Regardless if a boiler itself has a minimum flow requirement, every hydronic heating system needs to be designed to carry the energy being created away from the boiler to avoid high temperature shut down.

What is a condensing boiler?

Any boiler can produce condensed flue gases, but not all boilers are designed and built to withstand the by products associated with flue gas condensation. Only boilers that have heat exchangers designed and constructed to withstand the acidic qualities of flue gas condensate should be put into systems designed with water temperatures that would cause condensing to occur. Any system with return water temperatures less than 60°C should have full condensing boilers designed into it, otherwise the boilers are subject to heat exchanger failure from flue gas corrosion. Examples of materials that cannot withstand flue gas condensate are copper and cast iron.

What is flue gas condensate?

When the vapours produced from combustion in a boiler change phase from a gas to a liquid, that liquid is referred to as condensate. This phase change occurs at the dew point of the vapor, which is approximately 57°C. The temperature of the water coming into a boiler will determine whether or not the vapours of combustion will be at temperatures that are subject to condensing.

When does condensing occur?

Condensing of flue gases is a natural process. The dew point of the flue gas (approximately 57°C for natural gas, varies for other fuels) determines at what temperature flue gases will begin to condense. When the vapours produced from combustion fall below that dew point temperature, a phase change occurs and the vapour becomes a liquid.

Why are condensing boilers more efficient?

The vapours produced from the combustion process in a boiler contain energy. Flue gas condensate contains approximately 0.645 kW/hr of energy per kg (latent heat of vaporisation). Instead of that energy remaining in the flue gas vapor phase and going up the stack, it is recaptured as sensible heat in the liquid phase. For one hour, every kilogram of condensate collected adds 0.645 kW/hr to the output capability of a boiler. For example, a 585 kW/hr input boiler operating at an efficiency of 88% would have an output of 515 kW/hr. The boiler is operated for an hour at this condition and 36.4 kg of condensate is collected. The overall thermal efficiency of this boiler is actually 92%.

515 + (0.645 x 36.4) = 538.
538 / 585 = 0.92 = 92%

When would condensing be discouraged?

If a boiler has not been specifically designed to operate in the temperature ranges associated with condensing operation, the flue gas condensate will corrode the heat exchanger. Examples of materials that cannot withstand flue gas condensate are copper and cast iron.

Thermal Fluid Systems

Is there a minimum flow requirement for a thermal fluid heater?

A minimum flow rate is required in order to maintain the appropriate velocities through the heater (typically 3-3.7 m/s). If the velocity is too low the film temperature could increase, potentially destroying the fluid.

What are the primary components in a thermal fluid system?

A typical system includes the heater, circulation pump, expansion tank and the user. Depending on the temperature requirements and the system design control valves may also be utilised.

How do I choose a thermal fluid?

The required operating temperature along with the physical properties (specific heat, maximum operating temperature, vapour pressure, specific gravity and coefficient of thermal expansion) of the fluid should be evaluated when choosing a thermal fluid. It is important to choose a fluid specifically designed for heat transfer as opposed to a multi-purpose oil.

Can thermal fluids be mixed?

Mixing different fluids and subjecting them to high temperatures can have unpredictable results. In addition, once fluids have been mixed, the baseline analysis of the fluid is no longer applicable making it difficult to perform an annual analysis of the fluid for degradation.

Why is an expansion tank required?

All thermal fluids expand as they are heated. The amount of expansion is based on the operating temperature, system volume and the coefficient of thermal expansion of the fluid. An expansion tank must be provided to accommodate the increased system volume at operating temperature. NOTE: All fluids expand at a different rate.

What types of materials (valves, piping, gaskets etc.) should be used with thermal fluid systems?

Typically, thermal fluid systems should use either carbon or stainless steel components. Brass, bronze, cast iron and aluminum are incompatible with thermal fluid. Piping should be schedule 40 seamless BS EN 10216 material or equivalent. Valves should be cast steel or ductile iron with steel or stainless steel trim. Gaskets should be rated for the temperature and pressure of the system. NOTE: Threaded connections larger than DN25 (1”) should not be used in the flow circuit.

What is a nitrogen blanket?

When an expansion tank is pressurised with nitrogen (to eliminate the possibility of exposure of the fluid to oxygen), it is said to have a nitrogen blanket.

When is a nitrogen blanket required?

A nitrogen blanket is required under the following conditions:

  • Systems not equipped with a cold-seal tank (allowing the expansion tank to be under 90°C)
  • Systems where the expansion tank is located outdoors
  • Systems where the inlet to the tank is not the highest point in the piping system.
  • Systems where the operating temperature exceeds the atmospheric boiling point of the fluid.

Can I operate the system above the thermal fluid’s flash point?

Typical thermal fluid systems are designed to operate above the fluid’s flash point and fire point but not above its auto ignition temperature.

What is the life span of thermal fluid.

Typically, thermal fluid will last between 5 and 8 years. Annual testing of the fluid is recommended.

What type of insulation should be used on thermal fluid systems?

The insulation should be a cellular foam glass non-absorbent insulation; Pittsburgh Corning Foamglass or equal.

What type of temperature control can be achieved with thermal fluid systems?

Within the turndown ratio of the heater, +/- 3°C can be achieved. By designing the system with primary/secondary loops, +/-1°C can be achieved.

Is the heater a pressure vessel?

The heater will be built and stamped to either ASME Code Section I or ASME Code Section VIII Div. 1 depending on requirements. FT-N models can be built to BS EN 13445 upon request.

What are the gas pressure requirements for thermal fluid heaters?

The gas pressure requirement will vary with the type of heater and burner chosen. FT-0080C thru FT-0400C require 35 mbar (higher gas pressures are available upon request), FT-0600C thru FT-0800C require 100 mbar (344 mbar max) and FT-1000C thru FT-1400C require 298 mbar (688 mbar max). For low emissions burners, please consult the factory.

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