Installation guide
Rinnai Continuous Flow Water Heating Specication Guide 02-13 | 11
It is important when designing
central water heating systems that
they are sized correctly. This will
extend the life of the system and
reduce ongoing maintenance and
servicing costs.
Design principles
1. The Rinnai system should be
regarded as a continuous flow
system with storage back-up.
2. There should be sufficient
Rinnai HD/EF water heaters
installed to supply peak hour
demand.
3. Sufficient storage should be
incorporated in the water
heating system to meet any
fluctuations in demand above
peak hour average flow. In
general 20% storage back-up
has proven to be sufficient
storage in most applications.
4. Only Rinnai HD/EF models
are warranted for commercial
use. In Rinnai’s current
commercial range, the Rinnai
HD200 units usually offer a
more economical solution.
The HD250/EF250 units are
normally used in smaller
installations where their
size provides a better flow
match, or where space may be
restricted.
Peak hour hot water demand
estimation
In the absence of other
information, the following
can be used to estimate peak
hour demand. This method of
estimation has proven adequate in
the past, however Rinnai accepts
no liability in respect of this
estimate.
Water use per person in peak hour
at 60 °C:
- 4-5 star hotel type accomm.
= 45 litres
- 3 star accomm.
= 30 litres
- Apartment buildings
= 25 litres
Adjustments should be made
as required for factors that are
known; high flow shower heads or
other fixtures, spa baths, or load
patterns where large numbers of
guests arrive or leave at the same
time (tour groups). Figures for
other applications are provided
in Appendix 3: Commercial sizing
guidelines (p. 57).
Pump sizing
Rinnai water heaters are
designed to maintain outlet
water temperatures at all times.
If the flow exceeds their heating
capacity they will reduce the flow
via an internal water flow valve
to maintain the set temperature.
For this reason installing a larger
pump will not increase system
performance, and pumps may be
damaged due to cavitation when
operating at reduced flows.
Rinnai
model
Flow per Rinnai
HD/EF water
heater installed
Head
required,
add pipe
allowance
HD200 0.3 L/sec 8 m
HD250 0.4 L/sec 13 m
EF250 0.4 L/sec 11 m
Pump timer
As a safety feature Rinnai water
heaters will only allow three
ignition attempts before locking
out. In order to reset the water
heater and allow further ignition
attempts, water flow must stop. If
ignition has not occurred and the
pump does not stop the water will
remain cold. Fitting a timer to the
pump power supply to periodically
shut down the pump for a few
seconds will allow the water heater
to reset.
Designing central water heating systems
Performance of Rinnai continuous flow units are directly related to hours of use and how
well they are maintained.
Sizing example
A four star hotel in Wellington has fifty rooms with an average occupancy of 1.4 people per room.
Peak hour estimate calculation
45 litres per person x 50 rooms x 1.4 persons per room = 3150 litres per peak hour at 60 °C
With an incoming mid-winter water temperature of 10 °C, a Rinnai HD200 will deliver 810 litres per hour at 60 °C. Refer
to the water flow and gas usage tables at the back of this guide for additional delivery rates for each Infinity model.
3150 ÷ 810 = 3.9 units = 4 x Rinnai Infinity HD200’s would be required.
Storage backup
20% of peak hour requirement: 3150 x 0.20 = 630 litres of storage backup required.