The Glitch
Overview: A system for supplying
several zones of space heating using series-connected fin-tube baseboard is
shown below. The intent is to also supply lots of hot water from the large
(80-gallon) indirect water heater.
Exercise:
The installer feels that a mix of primary/secondary piping along with some
“alternative techniques” is appropriate. See if you can find at least eight
details (or major design errors) in this layout.
The Fix
Here’s a listing of what’s intentionally
shown incorrectly:
1. Boilers need individual circulators with check valves.
2. Distribution system is an “undefined”
collection of secondary and “across the header” circuits.
3. “Primary
loop” circulator is pumping toward expansion tank connection.
4. Heat exchanger connections on indirect tank
are reversed (not counterflow).
5.
Piping and circulator serving indirect tank cannot convey flow needed
for 400,000 Btu/hr heat transfer.
6.
Indirect tank is located on cool end of “primary loop.”
7. Long series circuits of baseboard make
sizing difficult.
8. Purge
valves on some circuits are incorrectly shown.
A far better approach is
shown in The Fix drawing. Instead of series-connected baseboards, it uses
manifolds and homerun circuits to individual baseboards. This provides the same
water temperature to each baseboard and simplifies sizing. The option of
thermostatic radiator valves for room-by-room temperature control is now
possible.
This is not a primary/secondary system. The closely spaced
tees provide hydraulic separation between the “short/fat” headers and the
boiler piping, but no primary circulator is required. The indirect tank shows a
large internal heat exchanger capable of sinking the full 400,000 Btu/hr boiler
output into the DHW load. This coil is piped for counterflow heat exchange (in
at top, out at bottom). This tank can also be operated as a priority load.
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