G1: Geo Thermal System Flashcards
What does geothermal mean?
Heating / cooling from earth or ground sources
What is the heart of geothermal?
Heat pumps
How does a Heat pump work? (in a nut shell)
Uses the refrigeration cycle to convert low - temp heat from a source –> high temp heat
Outdoor air, groundwater, lakes and ponds, tubing embedded in the ground all provide what?
Free low temp heat
What is a Heat sink?
A place to dispose unwanted heat.
What is the closed loop circuit consist of that Refrigerant travels around?
1) Evaporator
2) Compressor
3) Condenser
4) Thermal or thermostatic expansion valve (aka TXV)
What does Source media mean?
Its air or water
Does heat move from high to low temp or low to high temp?
High to low temp
What happens in the heating side of the evaporation cycle?
1) refrigerant is colder than source media
2) passes by evaporator
heat from source media gets pick up by cold refrigerant
3) Heat picked up causes vaporization of refrigerant
What is Superheat?
Heat required to raise temp above saturation temp
Where does the heat needed for superheat come from?
Source media
What happens at the compressor stage?
1) electric motor compresses vaporized refrigerant
What does Charles law dictate?
Pressure / temp act as one
increase P = increase T
Decrease P = decrease T
Refrigerant gas leaving the compressor is at what temp?
120 F - 170 F
What is happening at the Condenser stage?
Heat is transfer to load media (water or air) / carries the heat away to the load
What happens to the refrigerant as it dumps heat?
Goes from high - pressure + High - temp vapour–>
high-pressure + cooler liquid
(AKA CONDENSES)
What is happening at the final stage?
1) High pressure liquid flows through the expansion valve
2) Refrigerant pressure is reduced / drop in pressure causes a drop in temp
3) cycle starts again
The expansion valve (aka TXV) operates on what principle?
Bernoulli’s principle = greater the velocity, the lower the pressure
Where is the refrigeration cycle used?
Refrigerators
freezers
room AC
dehumidifiers
water coolers
vending machines
heat-moving machines
What does non-reversible heat pump mean?
Only heats or
Only cools
How does a non-reversible heat pump work (in a nutshell)
Refrigerant moves through the components within a loop in one direction only
What is an example of a non - reversible heat pump?
On appliances -> refrigerators
In a cooling only scenario what is the vehicle for cooling?
The evaporator
In a heating only scenario what is the vehicle for heating?
The condenser
What does a Reversible heat pump use to reverse flow?
Reversing valve
What 2 functions change in a reversible system?
heating mode:
evaporator –> condenser
cooling mode:
condenser –> evaporator
reversible heat pumps commonly use 2 sets of what?
thermal expansion
check valves
What is the bi-directional (two way) TXV used for?
flow reversal of refrigerant
How are heat pumps classified?
1) Media they take heat from (the source)
2) Media they deliver it too (the load)
What are the 4 types of heat pumps?
1) Air to Air
2) Air to Water
3) Water to Air
4) Water to Water
What type of heat pump is most common residentially?
Air to Air heat pumps
What is a Strip Heater?
a supplemental electric heater
What does a strip heater do?
adds heat to the air stream if the heat pump’s output can’t keep up w/ the heat loss for the building
Does an Air - to - Air heat pump require a condensation line?
Yes
Damp surfaces of indoor coils will allow for what?
Dirt and dust to cling to indoor coil = plugs very small openings between fins
Is an Air to Air heat pump recommended for Nothern Canada?
Absolutely not.
Will need supplemental heat
Air to air heat pumps are not suitable where?
Temps that drop below - 18C (0F)
Large accumulations of snow / ice around outdoor units
Air -to - Water Heat pumps roughly act how?
Heat exchanger tank is built into the outdoor unit –> water is used as the heat transport to indoors
True or False: a Air - Water heat pump will need an anti - freeze solution + insulation.
True
Water source heat pumps is used when heat pumps draw low temp water from what?
Any other source other than air
Fluid that delivers heat to heat pump can be of what?
water or water-based antifreeze solution
(pulls water from: pond, stream, horizontal trenches, vertical wells)
Can a Water to Air heat pump be installed horizontally?
Yes (to install in attics or crawl spaces)
When using an indoor heat exchanger for cooling what must be remembered?
Liquid condensate must be collected / piped to a safe location
Water to Air and Water to Water heat pumps are similar how?
They extract low-temp from the same sources.
The load is different though
Why are water to water heat pumps more compact in comparison to water to air pumps?
They don’t have a large blower.
Water to water heat pumps can provide heat to what?
Radiant heating
Domestic hot water
How do heat pumps heat or cool?
By moving energy
On the heating side of heat pumps, How is heat and efficiency expressed?
heat = BTUH
Efficiency = Coefficient of Performance (COP)
On the cooling side of heat pumps, How is the cooling capacity and efficiency expressed?
Cooling = Tons of cooling
efficiency = Energy Efficiency Rating (EER)
What are things that can effect the heat pump’s heating capacity?
1) temp of source media
2) temp of load media
3) flow rates of source/ load media
The vertical left side of a heat pump represents what?
heating capacity in MBH or BTUH
What does the bottom of a heat pump graph represent?
Temp of the water that can be in contact w/ the evaporator (aka entering source water temp)
What do the 3 lines indicates on a heat pump graph?
The possible temps of water entering the condenser
(entering load temps)
Lowering the temp at the condenser would cause higher or lower BTUH output?
Higher
The higher the entering source water temp (bottom of graph) means what? (what happens to the heat capacity?)
The greater the heating capacity
The lower the entering load water temp (curved diagonal lines), means what to the heat capacity?
The greater the heating capacity
The higher the flow rate through the evaporator / condenser (solid vs dotted curved lines) means what in heat capacity?
The greater the heating capacity
A “ton” of cooling = what in BTUH?
12,000
What is Free heat?
the low-temp heat being absorbed from the heat source medium
The ratio in COP represents what?
How many units of heat output will be produced for every unit of electrical input energy used
The higher the COP, the efficiency is what?
Higher (more efficient)
When the source media temp is close to the load media temp, the higher or lower the heat pumps COP?
The higher
What is the Temperature Lift?
The temp difference between the source media and load media
The smaller the lift = higher COP
What are 2 things that represent the heat pumps cooling output?
Cooling capacity
EER (Energy Efficiency Ratio)
In a water to water heat pump, the EER is an expression of what?
How many BTUH it can deliver for every watt of electricity it takes to do so.
The higher the EER of a heat pump, the less what?
The less energy it requires to produce a certain amount of cooling
The EER is a function of what?
the entering source water temp / entering load water temp
What gathers heat from a source / rejects it to a load?
a heat pump
Why are air source heat pumps less desirable than their ground source counterparts?
Cold weather = low COP / low heating capacities
Hot weather = reduce cooling capacity / EER of air source heat pumps
Soil within a few feet of the surface acts as what?
a storage media for solar heat
What kind of pipe is used for underground earth loops
High - density Polyethylene (HDPE)
PeX
What is an Open - Loop System?
water is drawn from open sources (lakes, ponds, wells) –> is circulated via piping / dumped out back at source
What is a good heat medium on an open loop system?
pond or lake / deep wells (over 25’)
temp does not fluctuate
What collects heat?
the evaporator
What dissipates heat?
the condenser
What are 2 issues that can have a negative effect of the system (when dealing with water)?
1) water’s quantity
2) water’s quality
What is a rough estimate of how much water a heat pump needs at the condenser or evaporator?
3 gallons per min
True or False: residential wells are usually undersized for a heat pump to use.
True. As the well is for domestic potable water as well.
Does local, provincial / federal codes / laws have to be consulted prior to installing an Open looped system?
Yes
Deep wells are often high in what?
TDS (Total dissolved solids), silt, Ca, Mg carbonates (hardness), sulphur compounds, manganese and iron
How do the TDS effect heat pumps?
it can accumulate in piping / heat exchanger / cause high ongoing maintenance.
What can you do to avoid costs repairs / warranty issues?
Consult manufactures literature
Why is the pump elevated above the lake bottom on open loop systems?
to prevent silt from being drawn in
The submersible pump uses what kind of controller?
Variable speed controller
A wider temp differential indicates what?
a large thermal demand on the system
When there’s a large thermal demand on the system, what happens to the pump?
the pumps speed increase to try to maintain the preset temp drop.
What happens when thermal demand lessons + temp differential narrows?
The pump slows down
How is the water supplies?
Via pressure switch / hydro-pneumatic tank
When is a closed loop a good choice?
When open loop sources are not available or not allowed
How does a closed loop work?
Heating mode - extract low temp water from the earth
Cooling mode - reject it by circulating 100% water or water based anti-freeze via closed piping loops buried in the ground
Can closed loops be installed vertically or horizontally?
Both ways
The choice to use horizontal depends on…
available area
soil conditions
excavation equipment availability
How deep does piping have to be buried?
4 - 8 feet
What are Slinkies?
series of coils installed in a larger excavated area
What are the borehole diameter / depth?
6” diameter
125 - 150’ / ton of heat pump evaporator capacity
What kind of tubing is used in closed systems?
HDPE or PeX
Is the pipe pressure tested before or after installation?
before
What is Bentonite?
A grout mixture made of sand and expansive clay
The additional grout helps with what?
prevents any ground surface contaminants from making their way down into the aquifer
What kind of system is the supply and return tube from each system ran into?
A reverse - return piping configuration
What does DR mean?
Diameter ratio
What kind of DR is preferable for buried tubing?
11
the lower the DR - the thicker the pipe wall
What is a header?
a manifold with Tee connections into the main pipe.
How are closed underground loops accessible?
If located in a buried vault that is freeze protected or
aboveground structure
How can you get equal flow on a closed loop system?
loops must be connected to the main in a reverse - return configuration.
Loops must be of same length
Is having the manifold more beneficial inside or outside the building?
Inside - easier to balance equal flows then
How can you have control of an exterior manifold?
They can be mounted inside a buried, semi-buried or aboveground heated enclosure (aka vault)
Why should vaults have open bottoms?
- allows loops to come up and connect to manifolds
- prevents vault from becoming buoyant / floating upward
What are the length of tubing requirements for earth loops?
This is how earth loop lengths are calculated.
- used for heating + cooling loads
- the longer of the two lengths is picked
1) tubing diameter / wall thickness
2) depth of burial
3) heating / cool capacity of heat pump
4) max / min earth loop fluid temp during heating / cooling seasons
5) arrangement of tubing w/in trenches or boreholes
6) thermal conductivity, moisture content, density / structure of soil
The deeper the horizontal loops are buried ….
the less loop length is needed
Which scenario is more effective:
single loops spaced further apart or
multiple loops spaced closer together?
Single loops spaced further apart –> less trenching needed
What type of soil is preferable?
wet, dense soils
Will vertical or horizontal loops experience less soil temp changes? (and have more consistent w/ COP over winter months)
Vertical loops
Does turbulent flow provide more or less heat transfer than laminar flow?
more heat transfer
Should backfill have voids or air pockets?
No, air is more insulative than conductive
How should earth loops be tested?
pressure tested w/ compressed air to min 75 psi for 24 hours (w/ no drops in pressure)
How many circulators and high capacity purge valves will a closed loop system include?
2 of each
How are the circulators piped?
In series = high pressure
What are high capacity purge valves necessary for?
the filling process
Air can collect in the tubing and cause circulation problems. How can you get air out of the loops?
Purge the loops at high flow flow rate w/ temporary external pump
What kind of tubing is connects the heat pump to inlet / outlets to reduce vibration issues?
Reinforced flexible hose connections
What is power - purging?
forces air from the earth loops by high-velocity water
True or False: closed loop system will have to have a microbubble resorber (air separator)
True
What does a dirt separator do?
(needed on a closed loop system)
Keeps unwanted debris from collecting in the loops
What type of fluid is used in closed loop systems?
Antifreeze solutions using salt, glycol or alcohol additives.
Why aren’t Brine solutions used anymore?
they are corrosive –> affects ferrous components
Why aren’t alcohol based antifreeze fluids used?
They include solutions of ethanol and methanol which is flammable = not a great idea
What is the most widely used fluid for geothermal systems?
Propylene glycol
- food - grade
- non - flammable
- non corrosive
- non toxic
Can radiant flooring use geothermal heat?
Yes
What kind of emitters do radiant flooring use?
Ones that operate at the lowest temp
What is the max supply water temp for a single zone geothermal radiant heating system?
120 F —> 49C
The lower the supply water temp = the water for heating capacity / COP?
the higher for both
On larger heating - only systems w/ multiple zones (where all zones possibly need heat at the same time)
Install a buffer tank –> prevents heat pump from short cycling
The buffer tank is the what for the heat from the geothermal system?
The load / source for radiant floors
What does an outdoor reset control do?
Used to maintain the temp of water in the buffer tank
Are mixing valves needed for floor systems?
No
What is the biggest advantage to a reversible heat pump?
Provides both heating and cooling
What is chilled water?
water taken to low temps for use in cooling operations
If a building’s cooling system provides comfort for people, what must it provide?
it must lower air temp + moisture content
What temp do heat pumps provide chilled water at?
40 - 60F / 4 - 15C
What kind of impact will lower temps have?
impacts cooling capacity / EER of the heat pump
True or False: higher than 15C temps remove moisture from the air.
False: it will not
What is latent cooling?
the process of removing moisture from the air
What is the Dew point?
This is the point where the air is saturated
What happens happens to cooling of air below the ew point?
will result in the water vapour condensing into water
What is the dry bulb temp?
is the air’s thermometer - measured temp (using sensible heat)
What is the chilled water terminal unit?
equipment that intentionally uses chilled water to lower the temp of the air for cooling purposes.
What is the purpose of a drip pan?
collects / disposes of condensation
What kind of waste is condensation?
Clear water waste
What piping material is used for condensate lines?
Sch 40 PVC
Heat that is rejected by the system in its cooling mode can be diverted / used to heat what?
Domestic hot water
What rate has been proven to be effective at removing air / debris from the piping?
min 2 feet / second
What is a purge cart or purge barrel?
Is a powerful high-capacity purging pump
How does a purge pump work on a valved system?
loops are individually purged via purge point connections installed in every loop until no air in system is indicated
How does a purge pump work on a system with no valves?
Purge pump is connected to purge points in the supply / return mains
- this will take longer as water has to be pushed via the entire system / returned to the cart
What is the GPM for 3/4” tubing?
3.6 GPM
What is the GPM for 1” tubing?
5.7 GPM
What is the GPM for 1 1/4” tubing?
9.0 GPM
Before adding antifreeze what is recommended to do for 2 days?
Use 100% water
allows minor leaks to be dealt w/
air to be removed
dirt separator has removed debris
Where can we determine how much antifreeze is to be added?
Manufacturer’s literature
What range of mixture is used for glycol / water?
15 - 25%
What else does a purge pump provide?
pressurization the system to its operating pressure
What is the operating pressure?
20 - 30 psi
Is an expansion tank needed for a closed loop system?
Yes - dt expansion / contraction of fluid
True or False: a system using a 20% glycol solution needs a larger expansion tank than a system using 100% water.
True
How often should routine maintenance and performance checks of a heat pump system be done?
at least once a year
True or false: closed systems should remain closed
True
What should be checked on motors?
excessive noise
vibration
heat / amperage
Where should operating temps be checked?
at various location
Ex: evaporator and condenser
