Scale in Water to Water Heat Pump.

Water quality has come up as a major issue this year for the heating systems in Cheakamus Crossing.  High mineral content in the well water has created higher concentrations of minerals in the closed loop heating. The minerals of biggest concern, are calcium and iron.

The water supply is from the Whistler potable water supply, not, the District Energy System or Waste Water Treatment Plant, as some have asked.  It is certainly safe for consumption and people will even pay money to get the health benefits from mineral water, however, for a closed loop heating system, these minerals are a problem.

image of used copper piping
Calcium buildup on copper pipes

The copper pipes shown here, were recently cut out of a unit that had several leaking fittings. Water had been slowly seeping out through poorly connected pipe fittings.   As water leaks out, it is replaced by the boiler feed which adds fresh water and minerals to the system .   The pipe with the thick layer of calcium shown above, shows the bottom of the pipe, where heavier particles collect.  A  quick swipe along the inside, easily removes the layer of calcium, exposing the bare copper.  The calcium did not bond to the pipe, as  it would if on a  heated surface, however, it is still stuck.

The calcium can be removed or at least reduced from collecting in the piping with water treatment but not, by flushing.  It would take very high velocities to flush the calcium off the walls of this pipe.  Velocities, much higher than what can be achieved by draining the tank.

However, draining the buffer and adding fresh water,  will create more problems down the road.   For example,1-IMG_3098  the mineral scale shown here, is just some of  what was taken from one system that had a slow water leak that went unnoticed.   The build-up eventually caused the unit to shut down.  Now, a lengthy clean up process would have to be performed to remove all the scale.  Until then,  the scale will slowly build on to the heat exchanger plates, where it bakes onto the plates  and hardens,  like limestone.  Eventually, the unit shuts down on high pressure.

There have been contractors trying to sell flushing, as part of an annual preventive service which will actually have the opposite effect.  Flushing, is one thing that should be avoided except in extreme cases.

Fresh water contains oxygen, a key ingredient to rust.  Air bubbles trapped in the fresh water, can become trapped in various locations, adding minerals that  will build up over time.

For those that can actually access the drain at the bottom of the buffer tank, it may be possible, to bleed off some of the water with higher mineral  concentrations, from the bottom of the buffer tank but only after, it has settled over a long period.  Such as, September, after the water pump has been off all summer, there may be some sediment that can be removed.  Only drain off a few liters, at the most.   If the water has visible particles, then it may have helped.  If it is clear, then you may have done more harm than good.  If you break off that cheap little plastic valve, used as a drain fitting,  ( on some of the tanks) you will have definitely done more harm.

The piping practices are of concern on some units, which can affect the  life of the equipment, due to electrolysis.  This can shorten the life of the buffer tanks,  hot water tanks and other components.  I expect the  buffer tanks to last 20 years+ if properly maintained.   The larger hot water tanks, will be shorter due to the fresh water.

There are non-toxic ways to treat this water and to reduce the need for cleaning the heat exchangers.  However, you cannot flush your trouble away.

Water quality is key to the long term operation of these systems.   With proper treatment, the water can be improved at a reasonable cost and these heat pump systems, can run a very long time with very little or no maintenance.

 

 

Image of evaporator coil with ice formed on the bottom thrid

Evaporator Freezing

Frozen evaporators are a common problem with air conditioning systems. A typical evaporator coil will run at 40°F/4°C, if the coil temperature drops to 32°F/0°C, the coil will start to freeze. This reduces the efficiency of the system and can damage the equipment.  The evaporator can freeze and then thaw, when the compressor cycles off, so there may be no indication of a problem until the day you really need it.

When the load increases on an air conditioning system on hot summer days, it is not uncommon for the compressors to run continuously. If the coil is below freezing and with no off cycle,  the ice will build up on the coil as shown here.

On split AC systems, you may not be able to see the evaporator coil but you can see the copper piping.  If ice is forming on the suction line, it means the coil is likely to freeze. If the line is insulated, then pull back a little bit of the insulation to expose the pipe and see if frost forms.

Image of a frozen suction line and compressor on a Carrier roof top unit.
Frozen suction line on a Carrier roof top unit

The most common cause of a coil freezing is low air flow. As the ice covers the coil, the air flow is restricted and accelerates the freezing process. Other common causes are refrigerant leaks, low ambient temperature, undersized liquid lines and dirty filters.

 

 

 

Image of a clip on anti-ice control
Clip on Anti Ice Control

Anti-ice controls are common on large air conditioning system and can be installed on any air conditioning system to shut off the compressor when ice is detected. This is a safety device to protect the equipment under extreme conditions when something has gone wrong.  There are contractors that will use the anti-ice control to mask a problem with an installation and can go undetected for years. When the coil is freezing the unit will use a lot more energy, drip water outside of the drain pan and shorten the life of the equipment. If the AC coil is freezing up, there is a problem that needs to be corrected.