| Boiler Name | |
| Applicability | All boilers |
|---|---|
| Definition | A unique descriptor for each boiler, heat pump, central heating heat-exchanger or heat recovery device. |
| Units | None |
| Input Restrictions | User entry. Where applicable, this should match the tags that are used on the plans for the proposed design. |
| Baseline Rules | Boilers are only designated in the baseline model if the Baseline System is of type 1 (PTAC), type 5 (Packages VAV with Reheat) or type 7 (VAV with Reheat). |
| Boiler Fuel | |
| Applicability | All boilers |
|---|---|
| Definition | The fuel source for the central heating equipment. The choices are:
|
| Units | List (see above) |
| Input Restrictions | As designed |
| Baseline Rules | Same fuel as the proposed design |
| Boiler Type | |
| Applicability | All boilers |
|---|---|
| Definition | The boiler type. Choices include:
|
| Units | List (see above) |
| Input Restrictions | As designed |
| Baseline Rules | The boiler type will be a hot water boiler for baseline systems 1, 5 and 7, according to the baseline system descriptions from Table G3.1.1B. All other system types do not have a boiler. |
| Boiler Draft Type | |
| Applicability | All boilers |
|---|---|
| Definition |
How combustion airflow is drawn through the boiler. Choices are:
|
| Units | List (see above) |
| Input Restrictions | As designed. Default is natural draft. |
| Baseline Rules | The baseline boiler is always assumed to be a natural draft boiler. (G3.1.3.2) |
| Number of Identical Boiler Units | |
| Applicability | All boilers |
|---|---|
| Definition | The number of identical units for staging |
| Units | Numeric: integer |
| Input Restrictions | As designed. Default is 1. |
| Baseline Rules | The number of boilers in the baseline case is set as follows (G3.1.3.2). The baseline building has one boiler when it serves an area less than or equal to 15,000 ft². For larger service areas, the baseline building shall have two equally sized boilers. |
| Boiler Heat Loss | |
| Applicability | All boilers |
|---|---|
| Definition | The boiler or heat-exchanger heat loss expressed as a percentage of full load output capacity. This loss only occurs when the boiler is firing. |
| Units | Percent (%) |
| Input Restrictions | Default is 2% for electric boilers and heat-exchangers and 0% for fuel-fired boilers. If the user overrides the default, supporting documentation is required. |
| Baseline Rules | Prescribed at 2% for electric boilers and heat-exchangers. Prescribed at 0% for fuel-fired boilers, since this loss is already incorporated into the overall thermal efficiency, combustion efficiency or AFUE of the boiler. |
| Boiler Design Capacity | |
| Applicability | All boilers |
|---|---|
| Definition | The heating capacity at design conditions |
| Units | Btu/h |
| Input Restrictions | Unmet load hours shall not exceed 300. If they do, the proposed boiler capacity shall be increased incrementally until the unmet loads are reduced to 300 or less. |
| Baseline Rules |
The boiler is sized to be 25% larger than the peak loads of the baseline building. Baseline boilers shall be sized using weather files containing 99.6% heating design temperatures and 1% dry-bulb and 1% wet-bulb cooling design temperatures.
|
| Boiler Efficiency Type | |
| Applicability | All boilers |
|---|---|
| Definition | The full load efficiency of a boiler is expressed as one of the following:
|
| Units | List (see above) |
| Input Restrictions |
Annual Fuel Utilization Efficiency (AFUE), for all gas and oil-fired boilers with less than 300,000 Btu/h capacity.
|
| Baseline Rules | Same as proposed design |
| Boiler Efficiency | |
| Applicability | All boilers |
|---|---|
| Definition |
The full load efficiency of a boiler at rated conditions (see efficiency type above) expressed as a dimensionless ratio of output over input. The software must accommodate input in either Thermal Efficiency (Et) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows:
$1) 75\% \leq AFUE \textless\ 80\% $ $E_t= 0.1 \times AFUE + 72.5\% $ $2) 80\% \leq AFUE \leq 100\% $ $E_t=0.875 \times AFUE + 10.5\% $ |
| Units | Ratio |
| Input Restrictions | As designed |
| Baseline Rules | Boilers for the baseline design are assumed to have the minimum efficiency as listed in Table 6.8.1F from ASHRAE Standard 90.1-2007 or Table 6.2.1F from ASHRAE Standard 90.1-2001. |
| Boiler Part-Load Performance Curve | |||||||||||||||||
| Applicability | All boilers | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Definition |
An adjustment factor that represents the percentage full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows:
$$ Fuel_{partload} = Fuel_{design} \times F\!H\!eat\!P\!L\!C\, \left ( Q_{partload}, Q_{rated} \right )$$ $$ F\!H\!eat\!P\!L\!C = \Bigg ( a + b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \Bigg ) $$ where
|
||||||||||||||||
| Units | Ratio | ||||||||||||||||
| Input Restrictions | As designed. If the user does not use the default curve, supporting documentation is required. The software may auto-generate curves for other boiler types from descriptive type information such as boiler type, core, full or partial condensing, combustion air control, minimum unloading or staging, and return water temperature. | ||||||||||||||||
| Baseline Rules | The baseline building uses the default | ||||||||||||||||
| Boiler Minimum Unloading Ratio | |||||||||||
| Applicability | All boilers | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Definition |
The minimum unloading capacity of a boiler expressed as a percentage of the rated capacity. Below this level the boiler must cycle to meet the load. [table title="Default Minimum Unloading Ratios" id="default-minimum-unloading-ratios"]
|
||||||||||
| Units | Percent (%) | ||||||||||
| Input Restrictions | As designed. If the user does not use the default curve the software must indicate that supporting documentation is required on the output forms. | ||||||||||
| Baseline Rules | Use defaults. | ||||||||||
| Hot Water Supply Temperature | |
| Applicability | All boilers |
|---|---|
| Definition | The temperature of the water produced by the boiler and supplied to the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Baseline Rules | Use 180°F for baseline boiler (G3.1.3.3). |
| Hot Water Return Temperature | |
| Applicability | All boilers |
|---|---|
| Definition | The temperature of the water returning to the boiler from the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Baseline Rules | Use 130°F for baseline boiler design. |
| Hot Water Supply Temperature Reset | |
| Applicability | All boilers |
|---|---|
| Definition | Variation of the hot water supply temperature with outdoor air temperature. |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Baseline Rules | The hot water supply temperature should vary according to the following:
|
| Boiler Name | |
| Applicability | All boilers |
|---|---|
| Definition | A unique descriptor for each boiler, heat pump, central heating heat-exchanger or heat recovery device. |
| Units | None |
| Input Restrictions | User entry. Where applicable, this should match the tags that are used on the plans for the proposed design. |
| Baseline Rules | Boilers are only designated in the baseline model if the Baseline System is of type 1 (PTAC), type 5 (Packages VAV with Reheat) or type 7 (VAV with Reheat). |
| Boiler Fuel | |
| Applicability | All boilers |
|---|---|
| Definition | The fuel source for the central heating equipment. The choices are:
|
| Units | List (see above) |
| Input Restrictions | As designed |
| Baseline Rules | Same fuel as the proposed design |
| Boiler Type | |
| Applicability | All boilers |
|---|---|
| Definition | The boiler type. Choices include:
|
| Units | List (see above) |
| Input Restrictions | As designed |
| Baseline Rules | The boiler type will be a hot water boiler for baseline systems 1, 5 and 7, according to the baseline system descriptions from Table G3.1.1B. All other system types do not have a boiler. |
| Boiler Draft Type | |
| Applicability | All boilers |
|---|---|
| Definition |
How combustion airflow is drawn through the boiler. Choices are:
|
| Units | List (see above) |
| Input Restrictions | As designed. Default is natural draft. |
| Baseline Rules | The baseline boiler is always assumed to be a natural draft boiler. (G3.1.3.2) |
| Number of Identical Boiler Units | |
| Applicability | All boilers |
|---|---|
| Definition | The number of identical units for staging |
| Units | Numeric: integer |
| Input Restrictions | As designed. Default is 1. |
| Baseline Rules | The number of boilers in the baseline case is set as follows (G3.1.3.2). The baseline building has one boiler when it serves an area less than or equal to 15,000 ft². For larger service areas, the baseline building shall have two equally sized boilers. |
| Boiler Heat Loss | |
| Applicability | All boilers |
|---|---|
| Definition | The boiler or heat-exchanger heat loss expressed as a percentage of full load output capacity. This loss only occurs when the boiler is firing. |
| Units | Percent (%) |
| Input Restrictions | Default is 2% for electric boilers and heat-exchangers and 0% for fuel-fired boilers. If the user overrides the default, supporting documentation is required. |
| Baseline Rules | Prescribed at 2% for electric boilers and heat-exchangers. Prescribed at 0% for fuel-fired boilers, since this loss is already incorporated into the overall thermal efficiency, combustion efficiency or AFUE of the boiler. |
| Boiler Design Capacity | |
| Applicability | All boilers |
|---|---|
| Definition | The heating capacity at design conditions |
| Units | Btu/h |
| Input Restrictions | Unmet load hours shall not exceed 300. If they do, the proposed boiler capacity shall be increased incrementally until the unmet loads are reduced to 300 or less. |
| Baseline Rules |
The boiler is sized to be 25% larger than the peak loads of the baseline building. Baseline boilers shall be sized using weather files containing 99.6% heating design temperatures and 1% dry-bulb and 1% wet-bulb cooling design temperatures.
|
| Boiler Efficiency Type | |
| Applicability | All boilers |
|---|---|
| Definition | The full load efficiency of a boiler is expressed as one of the following:
|
| Units | List (see above) |
| Input Restrictions |
Annual Fuel Utilization Efficiency (AFUE), for all gas and oil-fired boilers with less than 300,000 Btu/h capacity.
|
| Baseline Rules | Same as proposed design |
| Boiler Efficiency | |
| Applicability | All boilers |
|---|---|
| Definition |
The full load efficiency of a boiler at rated conditions (see efficiency type above) expressed as a dimensionless ratio of output over input. The software must accommodate input in either Thermal Efficiency (Et) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows:
(6.8.1-1)
$1) 75\% \leq AFUE \textless\ 80\% $ $E_t= 0.1 \times AFUE + 72.5\% $ $2) 80\% \leq AFUE \leq 100\% $ $E_t=0.875 \times AFUE + 10.5\% $ |
| Units | Ratio |
| Input Restrictions | As designed |
| Baseline Rules | Boilers for the baseline design are assumed to have the minimum efficiency as listed in Table 6.8.1F from ASHRAE Standard 90.1-2007. |
| Boiler Part-Load Performance Curve | |||||||||||||||||
| Applicability | All boilers | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Definition |
An adjustment factor that represents the percentage full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows:
(6.8.1-2) $$ Fuel_{partload} = Fuel_{design} \times F\!H\!eat\!P\!L\!C\, \left ( Q_{partload}, Q_{rated} \right )$$ $$ F\!H\!eat\!P\!L\!C = \Bigg ( a + b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \Bigg ) $$ where
|
||||||||||||||||
| Units | Ratio | ||||||||||||||||
| Input Restrictions | As designed. If the user does not use the default curve, supporting documentation is required. The software may auto-generate curves for other boiler types from descriptive type information such as boiler type, core, full or partial condensing, combustion air control, minimum unloading or staging, and return water temperature. | ||||||||||||||||
| Baseline Rules | The baseline building uses the default | ||||||||||||||||
| Boiler Minimum Unloading Ratio | |||||||||||
| Applicability | All boilers | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Definition |
The minimum unloading capacity of a boiler expressed as a percentage of the rated capacity. Below this level the boiler must cycle to meet the load. [table title="Default Minimum Unloading Ratios" id="default-minimum-unloading-ratios"]
|
||||||||||
| Units | Percent (%) | ||||||||||
| Input Restrictions | As designed. If the user does not use the default curve the software must indicate that supporting documentation is required on the output forms. | ||||||||||
| Baseline Rules | Use defaults. | ||||||||||
| Hot Water Supply Temperature | |
| Applicability | All boilers |
|---|---|
| Definition | The temperature of the water produced by the boiler and supplied to the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Baseline Rules | Use 180°F for baseline boiler (G3.1.3.3). |
| Hot Water Return Temperature | |
| Applicability | All boilers |
|---|---|
| Definition | The temperature of the water returning to the boiler from the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Baseline Rules | Use 130°F for baseline boiler design. |
| Hot Water Supply Temperature Reset | |
| Applicability | All boilers |
|---|---|
| Definition | Variation of the hot water supply temperature with outdoor air temperature. |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Baseline Rules | The hot water supply temperature should vary according to the following:
|
| Boiler Name | |
| Applicability | All boilers |
|---|---|
| Definition | A unique descriptor for each boiler, heat pump, central heating heat-exchanger or heat recovery device. |
| Units | None |
| Input Restrictions | User entry. Where applicable, this should match the tags that are used on the plans for the proposed design. |
| Baseline Rules | Boilers are only designated in the baseline model if the Baseline System is of type 1 (PTAC), type 5 (Packages VAV with Reheat) or type 7 (VAV with Reheat). |
| Boiler Fuel | |
| Applicability | All boilers |
|---|---|
| Definition | The fuel source for the central heating equipment. The choices are:
|
| Units | List (see above) |
| Input Restrictions | As designed |
| Baseline Rules | Same fuel as the proposed design |
| Boiler Type | |
| Applicability | All boilers |
|---|---|
| Definition | The boiler type. Choices include:
|
| Units | List (see above) |
| Input Restrictions | As designed |
| Baseline Rules | The boiler type will be a hot water boiler for baseline systems 1, 5 and 7, according to the baseline system descriptions from Table G3.1.1B. All other system types do not have a boiler. |
| Boiler Draft Type | |
| Applicability | All boilers |
|---|---|
| Definition |
How combustion airflow is drawn through the boiler. Choices are:
|
| Units | List (see above) |
| Input Restrictions | As designed. Default is natural draft. |
| Baseline Rules | The baseline boiler is always assumed to be a natural draft boiler. (G3.1.3.2) |
| Number of Identical Boiler Units | |
| Applicability | All boilers |
|---|---|
| Definition | The number of identical units for staging |
| Units | Numeric: integer |
| Input Restrictions | As designed. Default is 1. |
| Baseline Rules | The number of boilers in the baseline case is set as follows (G3.1.3.2). The baseline building has one boiler when it serves an area less than or equal to 15,000 ft². For larger service areas, the baseline building shall have two equally sized boilers. |
| Boiler Heat Loss | |
| Applicability | All boilers |
|---|---|
| Definition | The boiler or heat-exchanger heat loss expressed as a percentage of full load output capacity. This loss only occurs when the boiler is firing. |
| Units | Percent (%) |
| Input Restrictions | Default is 2% for electric boilers and heat-exchangers and 0% for fuel-fired boilers. If the user overrides the default, supporting documentation is required. |
| Baseline Rules | Prescribed at 2% for electric boilers and heat-exchangers. Prescribed at 0% for fuel-fired boilers, since this loss is already incorporated into the overall thermal efficiency, combustion efficiency or AFUE of the boiler. |
| Boiler Design Capacity | |
| Applicability | All boilers |
|---|---|
| Definition | The heating capacity at design conditions |
| Units | Btu/h |
| Input Restrictions | Unmet load hours shall not exceed 300. If they do, the proposed boiler capacity shall be increased incrementally until the unmet loads are reduced to 300 or less. |
| Baseline Rules |
The boiler is sized to be 25% larger than the peak loads of the baseline building. Baseline boilers shall be sized using weather files containing 99.6% heating design temperatures and 1% dry-bulb and 1% wet-bulb cooling design temperatures.
|
| Boiler Efficiency Type | |
| Applicability | All boilers |
|---|---|
| Definition | The full load efficiency of a boiler is expressed as one of the following:
|
| Units | List (see above) |
| Input Restrictions |
Annual Fuel Utilization Efficiency (AFUE), for all gas and oil-fired boilers with less than 300,000 Btu/h capacity.
|
| Baseline Rules | Same as proposed design |
| Boiler Efficiency | |
| Applicability | All boilers |
|---|---|
| Definition |
The full load efficiency of a boiler at rated conditions (see efficiency type above) expressed as a dimensionless ratio of output over input. The software must accommodate input in either Thermal Efficiency (Et) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows:
(6.8.1-1)
$1) 75\% \leq AFUE \textless\ 80\% $ $E_t= 0.1 \times AFUE + 72.5\% $ $2) 80\% \leq AFUE \leq 100\% $ $E_t=0.875 \times AFUE + 10.5\% $ |
| Units | Ratio |
| Input Restrictions | As designed |
| Baseline Rules | Boilers for the baseline design are assumed to have the minimum efficiency as listed in Table 6.8.1F from ASHRAE Standard 90.1-2007. |
| Boiler Part-Load Performance Curve | |||||||||||||||||
| Applicability | All boilers | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Definition |
An adjustment factor that represents the percentage full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows:
(6.8.1-2) $$ Fuel_{partload} = Fuel_{design} \times F\!H\!eat\!P\!L\!C\, \left ( Q_{partload}, Q_{rated} \right )$$ $$ F\!H\!eat\!P\!L\!C = \Bigg ( a + b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \Bigg ) $$ where
|
||||||||||||||||
| Units | Ratio | ||||||||||||||||
| Input Restrictions | As designed. If the user does not use the default curve, supporting documentation is required. The software may auto-generate curves for other boiler types from descriptive type information such as boiler type, core, full or partial condensing, combustion air control, minimum unloading or staging, and return water temperature. | ||||||||||||||||
| Baseline Rules | The baseline building uses the default | ||||||||||||||||
| Boiler Minimum Unloading Ratio | |||||||||||
| Applicability | All boilers | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Definition |
The minimum unloading capacity of a boiler expressed as a percentage of the rated capacity. Below this level the boiler must cycle to meet the load.
Table 6.8.1-1: Default Minimum Unloading Ratios
|
||||||||||
| Units | Percent (%) | ||||||||||
| Input Restrictions | As designed. If the user does not use the default curve the software must indicate that supporting documentation is required on the output forms. | ||||||||||
| Baseline Rules | Use defaults. | ||||||||||
| Hot Water Supply Temperature | |
| Applicability | All boilers |
|---|---|
| Definition | The temperature of the water produced by the boiler and supplied to the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Baseline Rules | Use 180°F for baseline boiler (G3.1.3.3). |
| Hot Water Return Temperature | |
| Applicability | All boilers |
|---|---|
| Definition | The temperature of the water returning to the boiler from the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Baseline Rules | Use 130°F for baseline boiler design. |
| Hot Water Supply Temperature Reset | |
| Applicability | All boilers |
|---|---|
| Definition | Variation of the hot water supply temperature with outdoor air temperature. |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Baseline Rules | The hot water supply temperature should vary according to the following:
|
|
Boiler Name |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
A unique descriptor for each boiler, heat pump, central heating heat-exchanger or heat recovery device. |
|
Units |
None |
|
Input Restrictions |
User entry. Where applicable, this should match the tags that are used on the plans for the proposed design. |
|
Baseline Rules |
Boilers are applicable to baseline HVAC systems 1, 5, 7, and 12. |
|
Boiler Fuel |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
The fuel source for the central heating equipment. The choices are:
|
|
Units |
List (see above) |
|
Input Restrictions |
As designed |
|
Baseline Rules |
For baseline HVAC systems that have a boiler, the fuel shall be gas, unless the proposed design has a boiler that uses oil or propane, in which case, the baseline HVAC system shall be the same as the proposed design. |
|
Boiler Type |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
The boiler type. Choices include:
|
|
Units |
List (see above) |
|
Input Restrictions |
As designed |
|
Baseline Rules |
Hot water boiler when the baseline building has a boiler |
|
Boiler Draft Type |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
How combustion airflow is drawn through the boiler. Choices are:
Natural draft boilers use natural convection to draw air for combustion through the boiler. Natural draft boilers are subject to outside air conditions and the temperature of the flue gases. Mechanical draft boilers enhance the air flow in one of three ways: 1) induced draft, which uses ambient air, a steam jet, or a fan to induce a negative pressure which pulls flow through the exhaust stack; 2) forced draft, which uses a fan and ductwork to create a positive pressure that forces air into the furnace, or 3) balanced draft, which uses both induced draft and forced draft methods to bring air through the furnace, usually keeping the pressure slightly below atmospheric. |
|
Units |
List (see above) |
|
Input Restrictions |
As designed. Default is natural draft. |
|
Baseline Rules |
Natural draft when the baseline building has a boiler |
|
Number of Identical Boiler Units |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
The number of identical units for staging |
|
Units |
Numeric: integer |
|
Input Restrictions |
As designed. Default is 1. |
|
Baseline Rules |
The baseline building shall have one boiler for a when the baseline plant serves a conditioned floor area of 15,000 ft² or less, and have two equally size boilers for plants serving more than 15,000 ft². Boilers shall be staged as required by the load. |
|
Boiler Heat Loss |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
The boiler or heat-exchanger heat loss expressed as a percentage of full load output capacity. This loss only occurs when the boiler is firing. |
|
Units |
Percent (%) |
|
Input Restrictions |
Default is 2% for electric boilers and heat-exchangers and 0% for fuel-fired boilers. If the user overrides the default, supporting documentation is required. |
|
Baseline Rules |
Prescribed at 2% for electric boilers and heat-exchangers. Prescribed at 0% for fuel-fired boilers, since this loss is already incorporated into the overall thermal efficiency, combustion efficiency or AFUE of the boiler. For boilers with efficiency rating prescribed as combustion efficiency, 2% jacket losses will be assumed. Therefore: Et = Ec – 2% Where, Et = Thermal Efficiency Ec = Combustion Efficiency |
|
Boiler Design Capacity |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
The heating capacity at design conditions |
|
Units |
Btu/h |
|
Input Restrictions |
Unmet load hours shall not exceed 300. If they do, the proposed boiler capacity shall be increased incrementally until the unmet loads are reduced to 300 or less. |
|
Baseline Rules |
The boiler is sized to be 25% larger than the peak loads of the baseline building. Baseline boilers shall be sized using weather files containing 99.6% heating design temperatures. |
|
Boiler Efficiency Type |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
The full load efficiency of a boiler is expressed as one of the following:
|
|
Units |
List (see above) |
|
Input Restrictions |
AFUE, for all gas and oil-fired boilers with less than 300,000 Btu/h capacities. Et, for all gas and oil-fired boilers with capacities between 300,000 and 2,500,000 Btu/h. Ec, for all gas and oil-fired boilers with capacities above 2,500,000 Btu/h. |
|
Baseline Rules |
Same efficiency type relationship with capacity as described for proposed design |
|
Boiler Efficiency |
||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Applicability |
All boilers |
|||||||||||
|
Definition |
The full load efficiency of a boiler at rated conditions (see efficiency type above) expressed as a dimensionless ratio of output over input. The software must accommodate input in either thermal efficiency (Et), combustion efficiency (Ec), or annual fuel utilization efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows: (Equation 3.8.1-1) $$For\ 75\% \leq AFUE < 80\%, E_{t} = 0.1 \cdot AFUE + 72.5\%$$ $$For\ 80\% \leq AFUE \leq 100\%, E_{t} = 0.875 \cdot AFUE + 10.5\%$$ Where Ec is provided, Et shall be calculated as follows: (Equation 3.8.1-1) $$E_{t} = E_{c}- 2\%$$
All electric boilers will have an efficiency of 100%. For applicable software, heat input ratio shall be defined as the inverse of thermal efficiency. |
|||||||||||
|
Units |
Ratio |
|||||||||||
|
Input Restrictions |
As designed |
|||||||||||
|
Baseline Rules |
Boilers for the baseline design are assumed to have the minimum efficiency as listed below.
|
|||||||||||
|
Boiler Part-Load Performance Curve |
|||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Applicability |
All boilers |
||||||||||||
|
Definition |
An adjustment factor that represents the percentage full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows:
(Equation 3.8.1-2) $$Fuel_{partload} = Fuel_{design} \times FHeatPLC(Q_{partload}, Q_{rated})$$ $$FHeatPLC = a + b \cdot (\frac{Q_{partload}}{Q_{rated}}) + b \cdot (\frac{Q_{partload}}{Q_{rated}})^{2}$$ where
|
||||||||||||
|
Units |
Ratio |
||||||||||||
|
Input Restrictions |
As designed. If the user does not use the default curve, supporting documentation is required. The software may auto-generate curves for other boiler types from descriptive type information such as boiler type, core, full or partial condensing, combustion air control, minimum unloading or staging, and return water temperature. |
||||||||||||
|
Baseline Rules |
The baseline building shall use the defaults as described above. |
||||||||||||
|
Boiler Forced Draft Fan Power |
|
|---|---|
|
Applicability |
All mechanical draft boilers |
|
Definition |
The fan power of the mechanical draft fan at design conditions. The software shall convert the user entry of motor HP to fan power in Watts by the following equation: Fan Power (W) = Motor HP x 746 x 0.5 |
|
Units |
Horsepower |
|
Input Restrictions |
As Designed. |
|
Baseline Rules |
Not applicable |
|
Boiler Minimum Unloading Ratio |
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|---|---|---|---|---|---|---|---|---|---|---|---|
|
Applicability |
All boilers |
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|
Definition |
The minimum unloading capacity of a boiler expressed as a percentage of the rated capacity. Below this level the boiler must cycle to meet the load. Table 3.8.1-1: Default Minimum Unloading Ratios
|
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|
Units |
Percent (%) |
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|
Input Restrictions |
As designed. If the user does not use the default curve the software must indicate that supporting documentation is required on the output forms. |
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|
Baseline Rules |
Use defaults. |
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Boiler Minimum Flow Rate |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
The minimum flow rate recommended by the boiler manufacturer for stable and reliable operation of the boiler. |
|
Units |
gpm |
|
Input Restrictions |
As Designed. If the boiler(s) is piped in a primary only configuration in a variable flow system then the software shall assume there is a minimum flow bypass valve that allows the HW pump to bypass water from the boiler outlet back to the boiler inlet to maintain the minimum flow rate when boiler is enabled. Note that the boiler entering water temperature must accurately reflect the mixed temperature (colder water returning from the coil(s) and hotter bypass water) in order to accurately model boiler efficiency as a function of boiler entering water temperature. |
|
Baseline Rules |
0 gpm |
|
Hot Water Supply Temperature |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
The temperature of the water produced by the boiler and supplied to the hot water loop |
|
Units |
Degrees Fahrenheit (°F) |
|
Input Restrictions |
As designed |
|
Baseline Rules |
Use 180°F for baseline boiler |
|
Hot Water Return Temperature |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
The temperature of the water returning to the boiler from the hot water loop |
|
Units |
Degrees Fahrenheit (°F) |
|
Input Restrictions |
As designed |
|
Baseline Rules |
Use 130°F for baseline boiler design. |
|
Hot Water Supply Temperature Reset |
|
|---|---|
|
Applicability |
All boilers |
|
Definition |
Variation of the hot water supply temperature with outdoor air temperature. |
|
Units |
Degrees Fahrenheit (°F) |
|
Input Restrictions |
As designed |
|
Baseline Rules |
The hot water supply temperature should vary according to the following:
|
| Boiler Name | |
|---|---|
| Applicability | All boilers |
| Definition | A unique descriptor for each boiler, heat pump, central heating heat-exchanger, or heat recovery device |
| Units | None |
| Input Restrictions | User entry |
| Baseline Building | Boilers are only designated in the baseline model if the baseline system is of type 1 (PTAC), type 5 (Packages VAV with reheat) or type 7 (VAV with reheat) and system 11 for climate zones 3B to 8 and system 12 |
| Boiler Fuel | |
|---|---|
| Applicability | All boilers |
| Definition |
The fuel source for the central heating equipment. The choices are: · Gas · Oil · Electricity |
| Units | List (see above) |
| Input Restrictions | As designed |
| Baseline Building |
Buildings located in climate zones 3B, 3C and 4 through 8 shall use hot-water fossil fuel boilers. Boilers are not used for the baseline HVAC system for climate zones 0 to 3A. For fossil fuel systems where natural gas is not available for the proposed building site as determined by the rating authority, the baseline HVAC systems shall be modeled using propane as their fuel. |
| Boiler Type | |
|---|---|
| Applicability | All boilers |
| Definition |
The boiler type. Choices include: · Steam boiler · Hot water boiler · Heat-pump water heater |
| Units | List (see above) |
| Input Restrictions | As designed |
| Baseline Building |
The boiler type will be a hot water boiler for baseline systems 1, 5, 7, 11, and 12. All other baseline system types do not have a boiler |
| Boiler Draft Type | |
|---|---|
| Applicability | All boilers |
| Definition |
How combustion airflow is drawn through the boiler. Choices are: · Natural (sometimes called atmospheric) · Mechanical Natural draft boilers use natural convection to draw air for combustion through the boiler. Natural draft boilers are subject to outside air conditions and the temperature of the flue gases. Mechanical draft boilers enhance the airflow in one of three ways: 1) induced draft, which uses ambient air, a steam jet, or a fan to induce a negative pressure that pulls flow through the exhaust stack; 2) forced draft, which uses a fan and ductwork to create a positive pressure that forces air into the furnace; or 3) balanced draft, which uses both induced draft and forced draft methods to bring air through the furnace, usually keeping the pressure slightly below atmospheric. |
| Units | Units List (see above) |
| Input Restrictions | As designed. Default is natural draft. |
| Baseline Building |
The boiler for the baseline system shall be natural draft boiler |
| Number of Identical Boiler Units | |
|---|---|
| Applicability | All boilers |
| Definition |
The number of identical units for staging |
| Units | Numeric: integer |
| Input Restrictions | As designed. Default is 1. |
| Baseline Building |
The baseline building shall have one boiler when the baseline plant serves a conditioned floor area of 15,000 ft2 or less, and have two equally size boilers for plants serving more than 15,000 ft2 |
| Boiler Heat Loss | |
|---|---|
| Applicability | All boilers |
| Definition |
The boiler or heat-exchanger heat loss expressed as a percentage of full load output capacity. This loss only occurs when the boiler is firing. |
| Units | Percent (%) |
| Input Restrictions | Default is 2% for electric boilers and heat-exchangers and 0% for fuel-fired boilers. If the user overrides the default, supporting documentation is required. |
| Baseline Building |
Prescribed at 2% for electric boilers and heat-exchangers. Prescribed at 0% for fuel-fired boilers, since this loss is already incorporated into the overall thermal efficiency, or AFUE of the boiler. For boilers with efficiency rating prescribed as combustion efficiency, 2% jacket losses will be assumed. Hence: Et = Ec – 2% Where: Et = Thermal efficiency Ec = Combustion efficiency |
| Boiler design Capacity | |
|---|---|
| Applicability | All boilers |
| Definition |
The heating capacity at design conditions |
| Units | Btu/h |
| Input Restrictions | UMLH shall not exceed 300. If they do, the proposed boiler capacity shall be increased incrementally until the unmet loads are reduced to 300 or less. |
| Baseline Building |
Autosized, with a heating oversizing factor of 25%. Sizing calculations shall be based on the heating design day and cooling design day conditions, as defined in Section 3.1.5 of this document. Oversizing would be carried out at zone level where the sizing parameters would be applied to the zone design heating loads, but not the airflow rates. Refer to Section 2.7.2 of this document for more details. If the number of UMLH for the baseline exceeds 300, heating coil capacity may need to be increased along with system airflow as described in Section 2.7.2. of this document. |
| Boiler Efficiency Type | |
|---|---|
| Applicability | All boilers |
| Definition |
The full load efficiency of a boiler is expressed as one of the following: · Annual fuel utilization efficiency (AFUE) is a measure of the boiler’s efficiency over a predefined heating season. · Thermal efficiency (Et) is the ratio of the heat transferred to the water divided by the heat input of the fuel. · Combustion efficiency (Ec) is the measure of how much energy is extracted from the fuel and is the ratio of heat transferred to the combustion air divided by the heat input of the fuel. |
| Units | List (see above) |
| Input Restrictions |
AFUE for all gas and oil-fired boilers with less than 300,000 Btu/h capacity Et for all gas and oil-fired boilers with capacities between 300,000 and 2,500,000 Btu/h Ec for all gas and oil-fired boilers with capacities above 2,500,000 Btu/h |
| Baseline Building |
Same efficiency type relationship with capacity as described for proposed design |
| Boiler Efficiency | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Applicability | All boilers | ||||||||||||
| Definition |
The full load efficiency of a boiler at rated conditions (see efficiency type above) expressed as a dimensionless ratio of output over input. The software must accommodate input in either thermal efficiency (Et), combustion efficiency (Ec), or annual fuel utilization efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows: 1) 75%≤AFUE<80% ??=0.1×????+72.5% 2) 80%≤AFUE≤100% ??=0.875×????+10.5% Where Ec is provided, Et shall be calculated as follows: ??=??−2% All electric boilers will have an efficiency of 100%. For applicable software, heat input ratio shall be defined as the inverse of thermal efficiency. |
||||||||||||
| Units | Ratio | ||||||||||||
| Input Restrictions |
As designed |
||||||||||||
| Baseline Building |
Boilers for the baseline design are assumed to have the minimum efficiency as listed below (Standard 90.1-2019 Table G3.5.6)-
|
| Boiler Part-Load Performance Curve | |
|---|---|
| Applicability | All boilers |
| Definition |
An adjustment factor that represents the percentage full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows:
Where FHeatPLC = The fuel heating part load efficiency curve Fuelpartload = The fuel consumption at part load conditions (Btu/h) Fuel design = The fuel consumption at design conditions (Btu/h) Qpartload = The boiler capacity at part load conditions (Btu/h) Qrated = The boiler capacity at design conditions (Btu/h) a = Constant, 0.082597 b = Constant, 0.996764 c = Constant, -0.079361 |
| Units | Ratio |
| Input Restrictions | As designed. Supporting documentation is required for use of different curves. Default part load performance curves provided in COMNET Appendix H (COMNET 2017) can be used based on draft type. |
| Baseline Building |
The baseline building uses natural draft curve specified in Equation (51) above |
| Boiler Forced Draft Fan Power | |
|---|---|
| Applicability | All mechanical draft boilers |
| Definition |
The minimum unloading ratio is where the boiler capacity can no longer be reduced by unloading and must be false loaded to meet smaller heating loads. The minimum unloading capacity of a boiler expressed as a percentage of the rated capacity. Below this level the boiler must cycle to meet the load. |
| Units | Horsepower |
| Input Restrictions |
As designed The software shall convert the user entry of motor HP to fan power in watts by the following equation: Fan Power (W) = Motor HP ´ 746 x 0.5 |
| Baseline Building |
Not applicable |
| Boiler Minimum Unloading Ratio | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Applicability | All boilers | ||||||||||
| Definition |
The minimum unloading capacity of a boiler expressed as a percentage of the rated capacity. Below this level the boiler must cycle to meet the load. Table 80. Default Minimum Unloading Ratios
|
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| Units | Percent (%) | ||||||||||
| Input Restrictions |
As designed. If the user does not use the default value, the software must indicate that supporting documentation is required on the output forms. |
||||||||||
| Baseline Building |
Use Table 80 |
| Boiler Minimum Flow Rate | |
|---|---|
| Applicability | All boilers |
| Definition |
The minimum flow rate recommended by the boiler manufacturer for stable and reliable operation of the boiler |
| Units | gpm |
| Input Restrictions |
As designed If the boiler(s) is piped in a primary only configuration in a variable flow system, then the software shall assume there is a minimum flow bypass valve that allows the HW pump to bypass water from the boiler outlet back to the boiler inlet to maintain the minimum flow rate when boiler is enabled. Note that the boiler entering water temperature must accurately reflect the mixed temperature (colder water returning from the coil(s) and hotter bypass water) in order to accurately model boiler efficiency as a function of boiler entering water temperature. |
| Baseline Building |
25% of design flow rate. Pumping configuration as described in Section 3.7.5. |
| Hot Water Supply Temperature | |
|---|---|
| Applicability | All Boilers |
| Definition |
The temperature of the water produced by the boiler and supplied to the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions |
As designed |
| Baseline Building |
Use 180°F for baseline boiler |
| Hot Water Return Temperature | |
|---|---|
| Applicability | All Boilers |
| Definition |
The temperature of the water returning to the boiler from the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions |
As designed |
| Baseline Building |
Use 130°F for baseline boiler design |
| Hot Water Supply Temperature Reset | |
|---|---|
| Applicability | All Boilers |
| Definition |
Variation of the hot water supply temperature with OAT |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions |
As designed |
| Baseline Building |
The hot water supply temperature should vary according to the following: · 180°F when outside air is < 20°F · ramp linearly between 180°F and 150°F when outdoor air is between 20°F and 50°F · 150°F when outdoor air is > 50°F |
| Boiler Name | |
| Applicability | All boilers |
|---|---|
| Definition | A unique descriptor for each boiler, heat pump, central heating heat-exchanger or heat recovery device. |
| Units | None |
| Input Restrictions | User entry. Where applicable, this should match the tags that are used on the plans for the proposed design. |
| Boiler Fuel | |
| Applicability | All boilers |
|---|---|
| Definition | The fuel source for the central heating equipment. The choices are:
|
| Units | List (see above) |
| Input Restrictions | As designed |
| Boiler Type | |
| Applicability | All boilers |
|---|---|
| Definition | The boiler type. Choices include:
|
| Units | List (see above) |
| Input Restrictions | As designed |
| Boiler Draft Type | |
| Applicability | All boilers |
|---|---|
| Definition |
How combustion airflow is drawn through the boiler. Choices are:
|
| Units | List (see above) |
| Input Restrictions | As designed. Default is natural draft. |
| Number of Identical Boiler Units | |
| Applicability | All boilers |
|---|---|
| Definition | The number of identical units for staging |
| Units | Numeric: integer |
| Input Restrictions | As designed. Default is 1. |
| Boiler Heat Loss | |
| Applicability | All boilers |
|---|---|
| Definition | The boiler or heat-exchanger heat loss expressed as a percentage of full load output capacity. This loss only occurs when the boiler is firing. |
| Units | Percent (%) |
| Input Restrictions | Default is 2% for electric boilers and heat-exchangers and 0% for fuel-fired boilers. If the user overrides the default, supporting documentation is required. |
| Boiler Design Capacity | |
| Applicability | All boilers |
|---|---|
| Definition | The heating capacity at design conditions |
| Units | Btu/h |
| Input Restrictions | Unmet load hours shall not exceed 300. If they do, the proposed boiler capacity shall be increased incrementally until the unmet loads are reduced to 300 or less. |
| Boiler Efficiency Type | |
| Applicability | All boilers |
|---|---|
| Definition | The full load efficiency of a boiler is expressed as one of the following:
|
| Units | List (see above) |
| Input Restrictions |
Annual Fuel Utilization Efficiency (AFUE), for all gas and oil-fired boilers with less than 300,000 Btu/h capacity.
|
| Boiler Efficiency | |
| Applicability | All boilers |
|---|---|
| Definition |
The full load efficiency of a boiler at rated conditions (see efficiency type above) expressed as a dimensionless ratio of output over input. The software must accommodate input in either Thermal Efficiency (Et) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows:
(6.8.1-1) $1) 75\% \leq AFUE \textless\ 80\% $ $E_t= 0.1 \times AFUE + 72.5\% $ $2) 80\% \leq AFUE \leq 100\% $ $E_t=0.875 \times AFUE + 10.5\% $ |
| Units | Ratio |
| Input Restrictions | As designed |
| Boiler Part-Load Performance Curve | |||||||||||||||||
| Applicability | All boilers | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Definition |
An adjustment factor that represents the percentage full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows: (6.8.1-2) $$ Fuel_{partload} = Fuel_{design} \times F\!H\!eat\!P\!L\!C\, \left ( Q_{partload}, Q_{rated} \right )$$ $$ F\!H\!eat\!P\!L\!C = \Bigg ( a + b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \Bigg ) $$ where
|
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| Units | Ratio | ||||||||||||||||
| Input Restrictions | As designed. If the user does not use the default curve, supporting documentation is required. The software may auto-generate curves for other boiler types from descriptive type information such as boiler type, core, full or partial condensing, combustion air control, minimum unloading or staging, and return water temperature. | ||||||||||||||||
| Boiler Minimum Unloading Ratio | |||||||||||
| Applicability | All boilers | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Definition |
The minimum unloading capacity of a boiler expressed as a percentage of the rated capacity. Below this level the boiler must cycle to meet the load. [table title="Default Minimum Unloading Ratios" id="default-minimum-unloading-ratios"]
|
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| Units | Percent (%) | ||||||||||
| Input Restrictions | As designed. If the user does not use the default curve the software must indicate that supporting documentation is required on the output forms. | ||||||||||
| Hot Water Supply Temperature | |
| Applicability | All boilers |
|---|---|
| Definition | The temperature of the water produced by the boiler and supplied to the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Hot Water Return Temperature | |
| Applicability | All boilers |
|---|---|
| Definition | The temperature of the water returning to the boiler from the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Hot Water Supply Temperature Reset | |
| Applicability | All boilers |
|---|---|
| Definition | Variation of the hot water supply temperature with outdoor air temperature. |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Boiler Name | |
| Applicability | All boilers |
|---|---|
| Definition | A unique descriptor for each boiler, heat pump, central heating heat-exchanger or heat recovery device. |
| Units | None |
| Input Restrictions | User entry. Where applicable, this should match the tags that are used on the plans for the proposed design. |
| Boiler Fuel | |
| Applicability | All boilers |
|---|---|
| Definition | The fuel source for the central heating equipment. The choices are:
|
| Units | List (see above) |
| Input Restrictions | As designed |
| Boiler Type | |
| Applicability | All boilers |
|---|---|
| Definition | The boiler type. Choices include:
|
| Units | List (see above) |
| Input Restrictions | As designed |
| Boiler Draft Type | |
| Applicability | All boilers |
|---|---|
| Definition |
How combustion airflow is drawn through the boiler. Choices are:
|
| Units | List (see above) |
| Input Restrictions | As designed. Default is natural draft. |
| Number of Identical Boiler Units | |
| Applicability | All boilers |
|---|---|
| Definition | The number of identical units for staging |
| Units | Numeric: integer |
| Input Restrictions | As designed. Default is 1. |
| Boiler Heat Loss | |
| Applicability | All boilers |
|---|---|
| Definition | The boiler or heat-exchanger heat loss expressed as a percentage of full load output capacity. This loss only occurs when the boiler is firing. |
| Units | Percent (%) |
| Input Restrictions | Default is 2% for electric boilers and heat-exchangers and 0% for fuel-fired boilers. If the user overrides the default, supporting documentation is required. |
| Boiler Design Capacity | |
| Applicability | All boilers |
|---|---|
| Definition | The heating capacity at design conditions |
| Units | Btu/h |
| Input Restrictions | Unmet load hours shall not exceed 300. If they do, the proposed boiler capacity shall be increased incrementally until the unmet loads are reduced to 300 or less. |
| Boiler Efficiency Type | |
| Applicability | All boilers |
|---|---|
| Definition | The full load efficiency of a boiler is expressed as one of the following:
|
| Units | List (see above) |
| Input Restrictions |
Annual Fuel Utilization Efficiency (AFUE), for all gas and oil-fired boilers with less than 300,000 Btu/h capacity.
|
| Boiler Efficiency | |
| Applicability | All boilers |
|---|---|
| Definition |
The full load efficiency of a boiler at rated conditions (see efficiency type above) expressed as a dimensionless ratio of output over input. The software must accommodate input in either Thermal Efficiency (Et) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows:
(6.8.1-1) $1) 75\% \leq AFUE \textless\ 80\% $ $E_t= 0.1 \times AFUE + 72.5\% $ $2) 80\% \leq AFUE \leq 100\% $ $E_t=0.875 \times AFUE + 10.5\% $ |
| Units | Ratio |
| Input Restrictions | As designed |
| Boiler Part-Load Performance Curve | |||||||||||||||||
| Applicability | All boilers | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Definition |
An adjustment factor that represents the percentage full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows: (6.8.1-2) $$ Fuel_{partload} = Fuel_{design} \times F\!H\!eat\!P\!L\!C\, \left ( Q_{partload}, Q_{rated} \right )$$ $$ F\!H\!eat\!P\!L\!C = \Bigg ( a + b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \Bigg ) $$ where
|
||||||||||||||||
| Units | Ratio | ||||||||||||||||
| Input Restrictions | As designed. If the user does not use the default curve, supporting documentation is required. The software may auto-generate curves for other boiler types from descriptive type information such as boiler type, core, full or partial condensing, combustion air control, minimum unloading or staging, and return water temperature. | ||||||||||||||||
| Boiler Minimum Unloading Ratio | |||||||||||
| Applicability | All boilers | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Definition |
The minimum unloading capacity of a boiler expressed as a percentage of the rated capacity. Below this level the boiler must cycle to meet the load. [table title="Default Minimum Unloading Ratios" id="default-minimum-unloading-ratios"]
|
||||||||||
| Units | Percent (%) | ||||||||||
| Input Restrictions | As designed. If the user does not use the default curve the software must indicate that supporting documentation is required on the output forms. | ||||||||||
| Hot Water Supply Temperature | |
| Applicability | All boilers |
|---|---|
| Definition | The temperature of the water produced by the boiler and supplied to the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Hot Water Return Temperature | |
| Applicability | All boilers |
|---|---|
| Definition | The temperature of the water returning to the boiler from the hot water loop |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |
| Hot Water Supply Temperature Reset | |
| Applicability | All boilers |
|---|---|
| Definition | Variation of the hot water supply temperature with outdoor air temperature. |
| Units | Degrees Fahrenheit (°F) |
| Input Restrictions | As designed |