Operating instructions

8
A. Storage Tanks
Coupling the heat pump to the space conditioning heat
exchanger through a water storage tank is very common.
In fact, the only instance where these storage tanks are not
recommended is when the heat pump is coupled to a large
heat exchanger capable of absorbing the entire heating or
cooling capacity of the heat pump (see Figure 5). In
applications that use multiple smaller zones, storage tanks
absorb the relatively large amount of energy supplied by
the heat pump, in order to provide longer run times and
less compressor cycling for the heat pump. Storage tanks
also serve to dispense energy in small amounts so that the
conditioned zones have time to absorb heat without
requiring high discharge water temperatures. Insulated
hot water heaters are commonly used for storage tanks.
)Note: While all hot water tanks are insulated on the
top and sides, many do not have insulation on the bottom.
An insulated pad beneath uninsulated tanks will reduce
energy loss to the floor.
When properly sized, a storage tank eliminates many
problems with multiple zone hydronic systems. These
problems include excessive leaving water temperature if a
single zone cannot dissipate heat quickly enough, and
hydronic flow reduction through the heat pump when only
one zone is calling. This may occur because the hydronic
circulating pump is normally sized to provide the heat
pump’s required flow with all zones calling. When sizing
storage tanks to the heat pump, a good rule of thumb is
ten gallons of storage tank per ton of hydronic capacity.
The tank temperature can be controlled with a simple
aquastat or a setpoint controller. The setpoint controller
senses tank water temperature and outside air temperature
to increase the tank temperature as the outside air
temperature goes down. This control scheme provides the
highest heating efficiencies by requiring the lowest
possible water temperature to heat the space. Setting the
optimal design temperatures in the controller is difficult,
and the simple aquastat does have its advantages. To help
in setpoint control, the following equation can be used.
Reset Ratio = Design Water Temp – Indoor Design Temp
Indoor Design Temp – Outdoor Design Temp
Always check local codes to be sure hot water heaters can
be used as storage tanks. Using the electric elements in
the tank as a secondary heat source to the heat pump is
appealing in some applications, but special UL listing is
required by many local codes. Specially listed hot water
heaters are available.
B. Hydronic Side Circulators
Hydronic circulator pumps transfer the energy supplied
by ECONAR's hydronic heat pumps to the space
conditioning heat exchanger. When selecting a circulator,
be sure to select a quiet operating pump with the ability to
supply the required flow rate at the system pressure drop.
The circulator supplying the heat pump should be placed
in the water supply line into the unit to provide the best
pump performance. Individual zone circulators should
also be placed in the supply lines of the heat exchangers
they serve. These pumps are often used as the on/off
control mechanism for the zone they supply as shown in
Figure 4. Zone valves are also commonly used for this
purpose using a common pump (shown in Figures 3 and
6).
)Note: Select a common pump at the total flow of all
the zones and the highest pressure drop of any one
parallel zone.
Small Grundfos pumps (230 VAC) can be used as
circulator pumps. These pumps are impedance protected
and do not require additional fusing if powered directly
from the heat pump, since the heat pump is rated to accept
up to a 1/3 horsepower circulator. If impedance protected
pumps are not used, inline fuses should be supplied
according to code.
Pumps must be sized to provide the required flow to a
heat exchanger at its corresponding pressure drop. This
pressure drop can be calculated from the total pressure
drop through the piping, added to the pressure drop of the
space conditioning heat exchanger. The hydronic side
pressure drop through each particular heat pump is listed
in Table 3. This table can be used for sizing the
circulating pump between the hydronic side of the heat
pump and a storage tank.
Table 3 – Storage Tank Circulators
Hyd. Loop Grundfos
Series Flow (gpm) dP (psi) Circulator
29
4 1.5 15-42F (Brute)
36
5 1.7 15-42F (Brute)
42
6 2.8 15-42F (Brute)
52
7 4.8 26-116
59
9 7.0 26-116
67
11 11.7 26-116 x Two
98
15 4.0 26-116
120
18 4.5 26-116
380
54 4.0 N/A*
This table represents the minimum pump sizing required
to supply the heat pump's required hydronic side flow rate
at the pressure drop of the heat pump and 30 feet of 3/4"
type K copper tubing or combination of elbows and pipe
(1-1/4" pipe on 98, 120 series and 2” pipe on 380 series).
*Hydronic side circulators for GW3800’s should be sized
for each specific installation.
A common problem with circulator pumps is trapped air
in the system. This air accumulates in the suction port of
the circulator causing cavitation in the pump, which leads
to premature pump failure and noisy operation. The air
can be eliminated by completely purging the system or by
placing an air separator in the plumbing lines.