3.9.1.4 Water Heating Auxiliaries | COMNET

90.1-2019

External Storage Tank Insulation
Applicability	All water heating systems that have an external storage tank
Definition	Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s).
Units	R-value (h-ft²-°F/Btu)
Input Restrictions	As specified in manufacturer data and documented on the construction documents
Baseline Building	Heat loss associated with the storage tank in the baseline building shall meet the requirements for an unfired storage tank in the baseline standards (Standard 90.1-2019, Table 7.8), which is an insulation R‑value of 12.5. The surface area and location of the storage tank shall be the same as the proposed design.

External Storage Tank Area
Applicability	All water heating systems that have an external storage tank
Definition	Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This documents the entire exterior surface area of the tank.
Units	ft²
Input Restrictions	As specified in manufacturer specifications
Baseline Building	Same as proposed

External Storage Tank Location
Applicability	All water heating systems that have an external storage tank
Definition	Location of the storage tank, used to determine the heat loss rate and energy exchange with the surroundings
Units	List: Schedule, Zone, Outdoors
Input Restrictions	As designed
Baseline Building	Same as proposed

Heat Recovery
Applicability	Water heating systems that are coupled to heat recovery equipment
Definition	Building equipment such as air conditioners, chillers, gas-fired generators, and others produce thermal energy that may be recovered and used to heat water. The heat-producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat-producing equipment need to produce output hourly so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units	Data structure: depends on the equipment producing the heat
Input Restrictions	There are no restrictions, other than agreement with the construction documents
Baseline Building	The baseline building requirements for condenser heat recovery are documented in Section 3.8.7 of this manual

Solar Thermal
Applicability	Water heating systems with a solar thermal system
Definition	A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal. Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design. The solar fraction shall be estimated by the f-chart procedure for solar water heating systems.
Units	Data structure: will vary with the software and system details
Input Restrictions	As designed. The proposed design may have a combined space and water heating system.
Baseline Building	Not applicable

Combined Space Heating and Water Heating
Applicability	Projects that use a boiler to provide both space heat and water heating
Definition	A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units	Data structure
Input Restrictions	As designed. The proposed design may have a combined space and water heating system.
Baseline Building	The baseline building shall be modeled with separate space heating and water heating systems, according to the baseline system type and corresponding requirements in Section 3.1.1 and baseline water heating system type and requirements identified in Section 3.9.1 .