Drain an ice house by sloping a 20-30 cm gravel floor toward a central channel that leads out through a pipe to a soakaway downhill, and fit a water trap in the drain so that warm outside air cannot travel up the pipe into the pit. The flow is small: an ice house losing 1,400 kg of ice in a month sheds about 47 litres a day, so the drain is sized to stay clear, not to carry volume. Water that pools around the ice melts it much faster than air does.
Part of Ice Houses and Cold Storage
Meltwater drainage removes the water that forms as ice melts, without opening a path for heat to enter the store.
The Drain Is Both An Exit For Water And An Entrance For Heat
Meltwater has to leave: standing water around the ice carries heat to it far faster than air does. Still air conducts heat at about 0.026 W/m.K and liquid water at about 0.6, more than 20 times as much (see Thermal Insulation Basics). But a drain is a hole in the floor, and a hole to the outside is a pipe that warm air can climb. A good drain takes the water and shuts the door behind it.
What You Need
- Gravel — 20-30 cm of clean gravel over the floor.
- A drain channel and pipe — leading from the floor centre to a soakaway or outfall downhill. Clay, wood or stone channel all work. See Clay Pipes.
- A water trap — a U-shaped bend or a small sump that stays full of water.
- A screen — fine mesh over the outfall to keep out animals.
- A soakaway or outfall — a gravel pit or a ditch downhill of the ice house, clear of wells and houses. See Safe Outlets.
Method: Build The Drain
Step 1: Slope the floor. Grade the floor toward the centre channel before laying gravel, so water drains even if the gravel settles.
Step 2: Lay the gravel. Spread 20-30 cm of clean gravel. Ice rests on a layer of sawdust or straw above it, not on the gravel itself, so melt passes down.
Step 3: Lead the drain out. Run the pipe or channel from the floor centre out through the wall and downhill with a continuous fall. See Below-Grade Design for the length needed.
Step 4: Fit the trap. Build a U-bend, or a small sump with the outlet set below its inlet, in the drain run. Fill it with water after building. The standing water forms a seal that air cannot pass.
Step 5: Screen and protect the outfall. Cover the outfall with a mesh, and line it with stone so it does not erode. Keep it above the water level of any ditch it joins.
Step 6: Check it each season. Pour a bucket of water onto the gravel and watch it leave. A drain that backs up needs clearing.
Worked Example: How Little Water Moves
An ice house stores 7,000 kg of ice and, as an assumed round figure for illustration, loses 20 percent of it in one summer month.
- Ice melted: 7,000 x 0.20 = 1,400 kg.
- Water produced: 1,400 kg of ice makes 1,400 kg of water, which is 1,400 litres or 1.4 m3.
- Per day over 30 days: 1,400 / 30 = 47 litres, about 2 litres an hour.
A 5 cm pipe is far larger than that flow needs. Its size is chosen to resist blocking by silt and sawdust, not to pass volume. The soakaway must absorb 1.4 m3 a month, 0.047 m3 a day. At the 75 mm/h slow-soil rate, soil absorbs 0.075 x 24 = 1.8 m of depth a day, so the arithmetic area is 0.047 / 1.8 = 0.026 m2. Size the soakaway for access, cleaning and frozen ground, not for flow.
Common Mistakes
- No drain — water pools and melts the ice. The parent article warns that pooled water melts ice about five times faster.
- An open pipe to outside — warm air climbs the pipe into the pit. Fit the trap.
- A trap that dries out or freezes — it stops sealing or blocks. Check it, and keep the outfall frost-protected.
- Sawdust washing into the drain — it clogs. Keep a gravel layer between the sawdust and the drain, and screen the inlet.
- Draining toward a well or house.
Safety
A sealed pit with a damp organic floor can lose its oxygen
Wet sawdust and straw over a drain keep rotting, using up oxygen and releasing carbon dioxide, which pools at the bottom of a pit. A person can collapse within a few breaths. Never go below until the pit has been ventilated to the floor, never lower a flame to test the air, tether the person descending and keep an attendant at the top. See Ice House Construction.
What’s Next
- Learn next: Roof Design — shed the heat from above
- Combine with: Sawdust — insulation that must stay clear of the drain