Enertech Global
23
EAV - EME/EMD Rev. A Models
Installation and Operations Manual
Overview
Almost all air-to-water and water-to-water heat pumps
require a buffer tank. With the introduction of variable speed
compressors, the requirements have changed and are addressed
in this section. The purpose of a buffer tank is primarily to keep
the heat pump running long enough to prevent short cycling
when the hydronic load is much smaller than the heat pump
capacity. Another important use of the buffer tank is to decouple
the flow rate required for the heat pump from the flow rate of
the hydronic system, which is typically much less than the heat
pump requires. Heat pumps with single speed and two-stage
compressors almost always need more flow rate than the design
flow rate of the hydronic system, especially if only one zone is
calling for heating or cooling.
Variable speed heat pumps can operate at much lower
flow rates when capacity is reduced using a variable speed
compressor and variable speed pump. With the installation of a
pressure differential bypass valve or hydraulic separator, even a
small radiant floor heating zone (three or four 1/2” PEX circuits,
2 to 3 gpm), can allow a variable speed heat pump to operate
without the use of a buffer tank. In order to maintain the
minimum flow rate required for the heat pump (about 4 gpm),
part of the flow is returned to the heat pump through the bypass
valve, and the remainder is delivered to the hydronic zone. This
approach works well for radiant floor zones. Very small loads
will cause the heat pump to cycle, but the minimum flow rate
for the refrigerant circuit is always maintained. If a hydraulic
separator is used, full flow to the heat pump is achieved since
the separator decouples the hydronic system flow rate from the
heat pump flow rate, much like a buffer tank.
Systems that require cooling must utilize fan coils that are large
enough to allow sufficient run time to provide adequate latent
capacity. Fan coils smaller than two tons could cause the heat
pump to cycle too often, not allowing the system to maintain a
coil cold enough to provide good dehumidification. Therefore,
Enertech recommends that fan coils two tons and larger are
used with variable speed heat pumps. A buffer tank is required
when using smaller fan coils.
Background Information
Based upon Enertech’s experience with variable speed heat
pumps, purging air from the system is one of the biggest
challenges to a successful installation when a buffer tank is not
used. Besides preventing short cycling and decoupling pumping
systems, a buffer tank functions as an air separator. Single speed
and two-stage heat pumps with buffer tanks do not typically
experience problems with air in the system because water flow
to/from the unit is simply flowing through a small amount of
piping from the heat pump to the buffer tank. Any air in the
system ends up at the top of the buffer tank (the buffer tank is
an air/dirt separator). Even if air is in the hydronic piping (other
side of the buffer tank, opposite the heat pump-- radiant floor
zones, fan coils, etc.), the heat pump does not experience flow
issues because it is isolated from the system by the buffer tank.
A buffer tank is typically not needed for variable speed
heat pumps (see “Recommendations” section, below), but
fluctuations in flow rate or even an air-locked pump can occur if
there is still air in the system when a variable speed heat pump
is installed without a buffer tank.
Based upon experience, some piping arrangements are
nearly impossible to properly purge air, especially when using
undersized PEX tubing. Fan coils are particularly difficult to
purge. If piping to a fan coil is insufficiently sized, it’s difficult to
get enough flow rate to purge the coil. For example, when a 1”
pex pipe feeds a tee with 1” branches, the inability to get the
proper flow for purging will occur. This is especially true if a zone
valve is located at a fan coil and isolation valves are far away
from the tee. There are many more examples of piping systems
that either lack air separators or that are difficult to purge due to
the piping configuration/sizing.
Enertech Recommendations for All EAV Unit
Applications
Based upon existing installations,
Enertech recommends that all
EAV variable speed air-to-water installations include a hydraulic
separator
to help lessen issues with air in the system and
isolate the heat pump from the hydronic system (radiant floor
manifolds, fan coils, etc.).
Figure 12b
shows typical piping when
a hydraulic separator is incorporated into the design.
Following is a detailed list of recommendations for variable
speed heat pumps:
Systems with fan coil(s) 2 tons or larger:
System should include
a hydraulic separator (Figure 12b).
Systems with fan coil(s) smaller than 2 tons:
System should
include a buffer tank (Figure 12c).
Zone Piping
: All zone piping should be “Home Run” style (Figure
12e) to assist with purging air and to maintain lower pressure
drop.
Hydronic Components:
System should include a boiler trim
kit that includes an expansion tank, air separator/automatic
air vent, pressure reducing valve, and backflow preventer.
In addition, an automatic air vent should be located at the
highest point in the piping system. Note that a factory-installed
expansion tank is included with the Indoor Module.
Antifreeze:
All systems must include antifreeze in the hydronic
piping and Fernox F1 inhibitor or approved alternate (this is a
warranty requirement). Heating only systems do not require
antifreeze in the hydronic piping (except those that have exposed
piping) but must include Fernox F1 inhibitor or approved
alternate (this is a warranty requirement).
⚠
NOTICE
⚠
Due to the monoblock design of the system, water piping
is exposed to the outdoors. Piping must be insulated and
sufficient antifreeze must be used to provide burst protection
below the lowest expected outdoor temperature.
Flush Valves:
System should include flush valves as shown in
Figures 12b and 12c to facilitate purging of air.
Section 3 - Installation Considerations
