Dhw Pump Sizing; System Zone Control; Priority Or Non-Priority For Hot Water - Baxi H2O 40 GL Manuel D'installation, D'utilisation Et D'entretien

Table 2. Parameters and Working Pressure Rating
Storage
Volume
Model
Gallon
H2O 40 GL 42
H2O 50 GL 53
H2O 80 GL 79
Table 3. Performance Rating
First Hour Draw
GPH
Model
140° F
H2O 40 GL 175
H2O 50 GL 187
H2O 80 GL
204
Note: All ratings are based on 50° F cold DHW water inlet.

3. DHW Pump Sizing

Refer to Table 3 for minimum flow through the water heater coil and pressure drop at the required boiler water flow rate. Calculate the pressure drop
across all pipes and fittings connecting the indirect water heater and hot water boiler. Be sure to include all ball valves, check valves, etc. It is manufacturer
recommended that the indirect water heater loop be piped with 1" pipe around the entire loop on typical residential sites.

4. System Zone Control

The water heater shall be installed as a separate zone from the space heating zones. If the indirect water heater pump and space heating pump run at the
same time (non-priority), the water heater zone's piping and circulator must be sized for the minimum flow rate with all the zones in use and maximum flow
with only the water heater in use. The three most common systems are:
• Central heating zone circulators and indirect tank circulator. Space heating zones use a circulator for each zone. The water heater is controlled with
additional circulator (DHW pump).
• Central heating system circulator and indirect tank circulator. One heating system pump is used for all space heating zones. Each heating zone has
one zone valve. The indirect water heater is controlled with additional indirect tank circulator.
• Central heating zone valves and indirect tank zone valve. Space heating zones use zone valves for each zone. The water heater is controlled with an
additional zone valve. In such system, indirect tank shall use a low pressure drop zone valve. Adequate boiler water flow through the indirect tank coil
must be assured.

5. Priority or Non-Priority for Hot Water

.
Priority The demand for space heating is interrupted until the hot water demand is satisfied or priority time is reached. This option provides the reliable
delivery of hot water. Priority is recommended when:
• The boiler output is less than 100,000 Btu per hour.
• Heating capacity required by the indirect tank is more than 50% of the heating capacity needed for space heating demand.
• When an interruption in space heating can be tolerated during long domestic hot water draws.
In most cases the delay in space heating will not be noticed because of the rapid recovery of the indirect water heater. It must be recognized however that
certain water heater malfunctions, such as a failed thermostat or circulator, could delay space heating indefinitely, if priority time is not established.
.
Non-Priority The boiler output is divided between space heating and the indirect water heater. Heating of domestic hot water can be reduced during
simultaneous space and water heating demands. The amount of reduction depends on boiler output, number of space heating zones calling, and amount of
boiler water flow split between space heating zones and water heater zone.
Coil Heating Maximum Working Pressure
Surface
DHW
ft
2
Water
14 150
14 150
20.7 150
Continuous Draw
GPH
115° F 140° F 115° F
198 138 162
212 144 169
228 140 164
(psi)
Boiler Water
116
116
116
Boiler Output Boiler Water ∆P Through
Required Flow
MBH GPM FT Water
105 14
110 14
110 14
7
Coil
10.7
10.7
15.9
PN 615000250 REV. B [01/09/2019]