307A geothermal, solar and heat recovery practice questions.

Five free practice questions on geothermal, solar and heat recovery: block F of the Red Seal 307A Steamfitter/Pipefitter exam, about 8 of its 130 questions. They are in the exam's format: four options, one correct answer. Answer each one before opening the explanation. No account, no email.

01The questions

1. Procedural · Installs piping for heat recovery systems

   A plate exchanger will recover heat from a dairy plant's pasteurizer cooling-water line, which must keep running when the exchanger is opened for cleaning. How is it piped?

   1. Isolation valves on each side, no bypass
   2. A bypass line with no isolation valves
   3. Isolation valves on each side plus a valved bypass
   4. A three-way diverting valve only
   Show the answer

   C. Correct. Isolation valves at the inlet and outlet let the exchanger be locked out and drained, and a valved bypass keeps the primary stream flowing while it is out, so heat recovery never blocks the process. Put vents and drains between the isolation valves and the exchanger so it can be drained and proven at zero energy.

   Why not the others

   A. Isolation alone lets the exchanger be removed, but the cooling-water line then stops, which is not allowed here. A valved bypass keeps the primary flow going.

   B. Without isolation valves the exchanger cannot be isolated, drained and locked out; the bypass would only share flow with it.

   D. A three-way valve can divert flow around the exchanger for control, but it is not positive isolation for opening the unit; isolation valves on both sides are still needed for LOTO and removal.

2. Procedural · Tests geo-exchange and geothermal systems

   A closed vertical loop at an arena has been fused, pressure-tested and connected to its flow centre. What is done before the antifreeze is added?

   1. Add the antifreeze, then purge with the loop pumps
   2. Fill slowly from city water and vent at the flow centre
   3. Purge with a purge cart at about 2 ft/s (0.6 m/s)
   4. Blow the loops out with compressed air
   Show the answer

   C. Correct. Each circuit is flushed with water from a purge cart at a velocity of about 2 ft/s (0.6 m/s) or more, which carries entrained air and construction debris back to the cart's open tank and filter; purging continues until no air returns. Antifreeze goes in after, and the loop is purged again to mix it. Air left in the loop causes poor flow and noisy, eroding pumps.

   Why not the others

   A. The flow-centre circulators cannot develop purge velocity through the whole field, and the debris would end up in the heat pump. The loop is purged with water first, then antifreeze is added.

   B. A slow fill leaves air pockets in the long runs and U-bends because the velocity is too low to carry the air out. Earth loops need a high-velocity purge, not a slow fill and vent.

   D. Blowing out with air adds air rather than removing it, and compressed air in a long plastic loop is a stored-energy hazard. Air and debris are removed with water at purge velocity.

3. Procedural · Tests solar heating systems

   A new rooftop glycol collector loop will be filled and hydrostatically tested on a sunny July afternoon. What is done before filling starts?

   1. Open the collector relief valve to vent during the fill
   2. Cover the collectors so the absorbers are cool
   3. Fill with plain water, then add glycol next month
   4. Fill fast at full pump flow to cool the absorbers
   Show the answer

   B. Correct. Empty collectors in full sun get very hot, and fluid pumped into them flashes to steam, causing pressure surges, glycol damage and burn hazards. Cover the collectors (or fill early or late in the day), then fill with the specified glycol mix through the fill and purge valves, vent the air and bring the loop up to the test pressure.

   Why not the others

   A. The relief valve is a safety device, not a vent; forcing it open can damage the seat and leave it leaking. Air leaves through the fill and purge valves and high-point vents, and the relief stays in service.

   C. Water left in the collectors can freeze and split them before the glycol goes in, and topping up later dilutes the mix below the freeze protection needed. Fill and test with the specified water/glycol mix.

   D. Pumping into hot absorbers flashes the first fluid to steam however fast it is pumped, and the steam can blow back toward the fill cart. The collectors are covered first.

4. Recall · Installs equipment for heat recovery systems

   At a pulp mill's turbine generator, steam leaking past the turbine gland seals is drawn off to a gland steam condenser. What stream absorbs and recovers that heat?

   1. The turbine lube oil in its oil reservoir
   2. The condensate returning to the deaerator
   3. The circulating water from the cooling tower
   4. The boiler bottom blowdown line
   Show the answer

   B. Correct. The gland steam condenser is cooled by the plant's own condensate on its way back to the deaerator, so the gland leak-off heat returns to the feedwater cycle and the condensed leak-off is recovered. A small exhauster keeps the glands slightly below atmospheric pressure so steam does not blow into the turbine hall.

   Why not the others

   A. Lube oil must be kept cool, and steam getting into the oil is a problem to prevent (water contamination), not a heat-recovery path.

   C. Rejecting gland steam to cooling-tower water would throw the heat away instead of recovering it. The point of the gland steam condenser is to put that heat back into the condensate.

   D. Bottom blowdown is a discharge of concentrated boiler water to a blowdown tank; it is a heat source in its own right, not a cooling medium for gland steam.

5. Recall · Installs piping for geo-exchange and geo-thermal systems

   Why is the supply and return header of a multi-bore vertical geo field often piped reverse-return?

   1. Each circuit has the same total path length
   2. Air collects at the first bore for venting
   3. It halves the pump head the loop needs
   4. The loops can drain back to the flow centre
   Show the answer

   A. Correct. In reverse return the first bore supplied is the last returned, so every U-bend circuit has about the same length of header plus loop, the same pressure drop and about the same flow without balancing valves. In direct return the circuits nearest the flow centre take more flow, so circuit balancing valves are needed.

   Why not the others

   B. Air is removed from an earth loop by purging with water at velocity from a purge cart, not by gathering it in one bore. The header arrangement is about equal flow between circuits.

   C. Reverse return adds some header length, if anything; it does not halve the total head. Its benefit is balance between parallel circuits, not a lower pump head.

   D. Closed earth loops run full and pressurized and are not designed to drain back. Draining back is a feature of some solar collector systems, not of geo headers.

02Answer key

03What block F covers

This block covers renewable energy and heat recovery systems. It includes geo-exchange and geothermal heat pumps with closed, open and DX loops, HDPE heat fusion, loop purging and antifreeze, solar water heating with glycol and drainback systems, stagnation and double-wall exchangers, and heat recovery from refrigeration, condensate, blowdown and process water through plate and shell-and-tube exchangers.

The Red Seal Occupational Standard names this block “Installs, tests, maintains, troubleshoots and repairs renewable energy systems”. It carries 6.2% of the exam, about 8 of the 130 questions, split across three tasks. The share column is each task's weight within the block, as the standard publishes it.

04What the questions turn on

Fusing and purging ground loops

Buried HDPE loop joints are heat-fused: butt fusion for like sizes, socket fusion or electrofusion for tees and branches. Before antifreeze goes in, each circuit is purged at about 2 ft/s (0.6 m/s) until no air returns to the cart.

Drainback versus pressurized glycol

A drainback loop slopes continuously toward its tank with no sags and has no check valve, because the collectors empty when the pump stops. A pressurized glycol loop needs a check valve to stop reverse thermosiphon at night.

Stagnation and glycol breakdown

When storage reaches its high limit the pump stops and the collectors stagnate. Repeated overheating breaks propylene glycol into acids, darkening it and dropping its pH. The expansion tank must also take the fluid pushed out of the collectors.

Double-wall exchangers

A double-wall exchanger has a gap vented to atmosphere between the two fluids, so a failed wall shows as fluid at the vent instead of mixing into potable water. Steady dripping from that vent means taking it out of service for repair.

05The other blocks

The 307A exam has seven blocks. Each has its own page of free questions:

The 307A Steamfitter/Pipefitter practice exam page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.