Glossary of Terms
The following is designed as an abbreviated non-technical, layman’s explanation of some of the concepts that may be helpful in understanding the application of the HotSpot heat recovery system. The terms and concepts are explained only to the level necessary.
Thermodynamics is a well established branch of science that deals with the study and manipulation of different forms of energy and the quantitative relationships between them. Thermodynamics engineering is central to creating systems that create, transport or store thermal energy.
First Law of Thermodynamics
The part of the 1st law that is relevant to our discussions is called the law of conservation of energy, which is an empirical law of physics. It essentially states that energy can neither be created nor destroyed, it can only be transformed into another form of energy. It can be moved from one location to another.
Second Law of Thermodynamics
The 2nd law states that over time, differences in temperature tend to balance out in an isolated system. This forms the basis for heat transfer and the operation of a heat exchanger, meaning that when a cooler mass (example, an object or fluid) is exposed to a warmer mass, heat will transfer in a direction from hot to cold. As heat is lost from the warmer mass it is absorbed by the cooler mass, which will rise in temperature. The greater the difference in temperature, the faster the heat will transfer. As the temperatures near each other the rate of transfer falls. If left in contact for sufficient time, the temperature of the two will attain equilibrium and heat transfer will stop.
Energy is the ability to perform work and is measured in various ways such as joules, watts, BTUs, etc. Energy can be found in various forms like potential energy, kinetic energy, thermal energy, electrical energy, chemical energy and others. Any form of energy can be converted to any other form of energy, for example electricity can be converted to heat through resistance, as done in an electric stove.
A BTU (British Thermal Unit) is the amount of energy needed to raise the temperature of one pound of water one degree. A BTU is a measurement of energy equal to 1.060 kJ (kilojoules), 0.293071 Wh (watt hours) or 253 cal (calories). You will often see "btu" used incorrectly, when what is meant is BTUs per hour. For example on a heater or air conditioner, the box might say "10,000 BTU" but it really means that the unit is rated to provide 10,000 BTU/hr. In most of the world outside of the USA, heating and air conditioning capacity is rated and measured in kilowatts of capacity rather than BTU of capacity. For example a 60,000 BTU rated system is the same thing as a 17.5 kW rated system. Sometime systems are rated in “tons”, a ton is the same thing as 12,000 BTUs per hour.
A watt is a basic unit of energy, and is essentially a product of amperes multiplied by the voltage.
A kilowatt is 1000 watts. Watts are used to measure the instantaneous energy a system consumes or produces. For example a 100 watt light bulb has a draw or power consumption of 100 watts, if left on for ten hours it would consume 1,000 watts or one kilowatt. In Europe and most of the world outside of the USA, the capacity of heating and cooling systems is stated in kilowatts.
Kilowatt Hour (kWh)
A kilowatt hour is a unit of energy, and is usually the billing unit for energy delivered to consumers by electric utilities, it is what you pay for when you pay your electric bill. A kilowatt hour is an amount of energy equal to 1000 watt hours, energy measured in watt hours is the multiplication of watts and time in hours. For example, a 1000 watt hair dryer running for one hour consumes one kilowatt hour. A 500 watt hair dryer operating for two hours also consumes one kilowatt hour. One kWh equals 3414 BTUs.
Heat is energy in motion from one region to another, as a result of a temperature difference. Heat can be created in various ways including friction, electrical (resistance) or chemical (combustion, etc.). Heat can also be moved from place to place, for example with a heat pump or air conditioner.
This is an acronym for the interconnected activities of Heating, Ventilation and Air Conditioning. It is also used as HVACR with the added “R” standing for refrigeration.
Cooling Capacity (Heat Rejection)
Typically the capacity of a refrigeration system is rated based on its heat rejection capacity. Cold cannot be created, cold is defined as the absence of heat. Low temperatures (cold) are created by moving or pumping the heat to another location where it can be rejected.
Ton (as used in the HVAC/R industry)
A ton of heat or air conditioning is equal to 12,000 BTUs. For example a 5-ton unit and a 60,000 BTU unit are the same size.
Whether used as part of a system for air conditioning or other cooling, freezing or heating (when used in a heat pump) a refrigeration compressor compresses a fluid so that the heat can be pumped from one place to another and then rejected into another area, like the outdoors. See: Refrigeration Cycle.
A heat pump is best described as an air conditioner that is designed to operate in either direction, a reversible air conditioner that can also serve as a heater. In the case of a heat pump operating in heating mode, this is a refrigeration cycle in which the heat is rejected indoors.
An air conditioner does not create cold, it removes heat, and typically consists of a compressor, an evaporator, a condenser and an expansion valve all connected in a sealed circuit through which a refrigerant (like Freon) fluid is circulated. As the fluid is pumped through the evaporator (indoor cooling component), indoor air is blown across the evaporator with a fan. The air is cooled and the fluid absorbs the heat from the air and becomes warmer. Then the warmer fluid is compressed by the compressor, concentrating the heat and making it very hot. At that point the highly compressed hot fluid is passed through the condenser, a sort of radiator located outside where cooler outdoor air is blown across it by a fan causing the heat to be dissipated into the outdoor air which cools the fluid. The fluid is then cooled to a very cold state as its pressure drops through an expansion valve, proceeding on toward the evaporator where the cycle repeats.
This stands for Energy Efficiency Ratio. It is a straight calculation of efficiency based on measured performance running at a set of standard testing conditions. The EER is calculated by dividing the BTUs rejected by the consumed watt hours. (Btu/Wh)=EER The higher the number, the more efficient the system.
This is the Energy Star and government test standard rating, it stands for Seasonal Energy Efficiency Ratio. It is the same as EER in that it is calculated using BTUs and watt hours but is more useful because instead of a fixed test point it measures the efficiency of the system across variable conditions, for example to see how it performs year round including the “shoulder seasons when the system is needed but the full capacity of the system is not needed. Systems with features like ground or water source, multi-stage or variable speed compressors, variable speed fans, etc. usually have a higher SEER rating.
Large commercial heating and cooling system efficiency is measured in COP which stands for Coefficient Of Performance. COP is calculated similar to EER except the watt hours are converted to BTU, or the BTU is converted to watts, before calculating. The calculation is still the same, i.e. output divided by input (w/w or btu/btu). It gives an easy to understand number, for example a 5 ton (17.5 kW) system consumes 5000 watts, it has a COP of 3.5 (17,500 / 5000 = 3.5). It provides 3.5 times more output than consumption. Note* This does not violate the 1st Law because we are not *creating* heating or cooling, we are only moving heat from one place to another.
Simply stated, the refrigeration system condenser causes the gas to condensate, turning hot gas into a cooler liquid. In a refrigeration system the condenser is the area where a fan blows cooler air across hot refrigerant filled coils or finned tubes, causing the loss or rejection of heat into the moving air. This action cools the refrigerant to below its boiling point, turning it into a liquid.
A fluid is a substance that will flow and can be pumped. A fluid can be a liquid or a gas, a fluid may change from gas to liquid and back again, depending on its current pressure and temperature. The oxygen we breathe is technically a fluid.
Refrigerants are fluids selected because they can successfully conduct or carry heat, and typically have a relatively low boiling point. “Freon” is a well known refrigerant although it has been banned due to environmental issues. Commonly in use today are R22, R410, R134 and a wide range of similar refrigerants tailored to specific performance goals. Other fluids that can be used as refrigerants include ammonia, lithium bromide, or even water in large scale or industrial refrigeration.
This refers to older, refrigerants banned because they are hydrochlorofluocarbons, which deplete the ozone layer and cause environmental problems.
Known as Freon, this was the standard in refrigeration for decades with a boiling point just under -40C and was used in everything from automobiles, refrigerators, air conditioners, etc. As a HCFC, it is banned and no longer used.
This refrigerant has been common in air conditioning and is still in use however it is a HCFC. It has been discontinued in the USA for new equipment, still used in existing equipment, will be completely phased out by 2020.
With a boiling point of 78F it is becoming the standard in commercial refrigeration, and automobiles. It is an environmentally friendly Non-HCFC refrigerant.
This is an environmentally friendly non-HCFC refrigerant that has a boiling point of -30.4 degrees F. This is the refrigerant now used in most new air conditioners.
A type of air conditioning system where the evaporator is in close contact with a second fluid such as water, propylene glycol, or a mix of the two, in an adjacent circuit. Heat exchange occurs, cooling the water. This type of air conditioning system pumps the cold water to other locations in the building where they feed fan + coil units. The fans blow air across the coils which cause the coils to absorb heat from the warmer air, making the air cooler.
A typical heat exchanger is a device that allows two fluids at different temperatures to exchange heat with each other without coming into contact with each other. The fluids could be air, water or other fluids. The fluids are separated from each other inside the heat exchanger by a thin single or double wall. The temperature differential causes heat to pass through the wall. A good example of a water-to-air heat exchanger is an automobile radiator, where a fan blows across the radiator fins and causes heat to be lost into the air, warming the air and cooling the water.
In a fresh water tank, the water will form a temperature gradient in a process called stratification. Stratification in a water heater means that the hottest water will be at the top of the tank and the coolest water at the bottom, this occurs because heat always rises. There is usually a large difference in temperature between the top and bottom of a hot water tank.
When a liquid changes its state into a gas, it is called evaporation. In an air conditioner system, the evaporator is the indoor component that gets cold. It may be a flat plate with refrigerant filled capillaries, coils, or other design. When warmer air is forced into contact with the evaporator, heat exchange occurs and as the cooler evaporator absorbs heat and the air is cooled. As this happens, the liquid refrigerant flowing in the evaporator absorbs the heat, raising its temperature towards its (very low) boiling point where it will evaporate into (convert to a gas).
Design Run Time
For our purposes, when we mention it we are referring to how compressors and walk-in coolers are designed. Calculations are made based on the R-value of the cooler, heat load, expected exfiltration, ambient indoor and outdoor temperatures etc. Compressors for walk-in coolers are sized so that they have a Design Run Time of 16 hours per day.
Head (Pump Head)
Refers to the power and sizing of a pump which is rated or sized by how much resistance it can or must overcome and is expressed by how high it can pump water, in a certain diameter pipe etc., at a specific flow rate and assumes an open system. In a closed system, head is calculated based on the pipe diameter, length, and the number of elbows or other flow impediments.
The amount of resistance a compressor must overcome is called head pressure. The amount of pressure is related to system resistance and the temperature of the fluid. The hotter a fluid gets, the higher the pressure will become.
This is a temperature sensor/switch. Its purpose it to activate or deactivate a system based on temperature dropping below freezing, and to then reverse the process when the temperature rises above freezing.
Hot Water Storage Tank
An insulated water tank, like a water heater tank, but without a built-in heating source.
A hot water storage tank can be added to a heat recovery installation to increase the capacity of hot water. In a pre-heat configuration, the HotSpot would heat the storage tank water. The storage tank outlet would connect to the inlet port of the main tank. When the main tank has a load and draws in fresh water, it comes from the pre-heat tank and is already hot.
Double Wall Heat Exchanger
Required by code in many water heating applications, a double wall insures that if a wall of either fluid tube in a heat exchanger were to break, its fluid would escape into the atmosphere through a vent and would not contaminate the other fluid.
A dryer is an inline filter installed in a refrigeration circuit. Its purpose it to trap water and other contaminants to keep them out of the compressor.
A Thermal Expansion Valve (TXV) is the separation point of the high pressure and low pressure sides of a refrigeration system. When refrigerant is released through the valve from the high pressure to low pressure, its temperature drops.
Temperature Pressure Valve. This is a valve that is a safety feature of every water heater. If the tank gets too hot or under too much pressure, the valve opens.
Tank Tap Adapter. The HotSpot Energy TTA is a device
that uses a hot water tank’s drain port to serve
as both an additional inlet and outlet port, and continue
to serve as a drain port.
Delta means differential, T mean temperature. Delta T means temperature differential. Usually expressed as ΔT.
Superheat is when a vapor’s temperature is above
its saturation temperature (boiling point) at a particular
Usually found in large scale industrial heat recovery, it is a heat exchanger that can remove part of the superheat and use the heat for other purposes. Some higher-end geothermal heat pump systems are now available for ordering with a factory installed desuperheater option for water heating.
A reversing valve is one of the components that that allows an air conditioner to run backwards and become a heat pump. The reversing valve is a 4-way valve that allows the same compressor to handle flow in both directions, while the compressor continues operating in its own normal direction.
Is a pressurized closed loop hot water application, an expansion tank is needed. This tank has a bladder that can hold expanded the water volume that occurs from the thermal expansion of water as it is heated. When the water is cool, the expansion tank is empty.
A boiler is a term for a water heater.
Hot Water Heater
Where we come from, we usually heat cold water. Seriously? It's a boiler.
A pressurized, usually vertical tank with a built in heating system that uses either an electric heating element or a gas burner and is controlled by a thermostat. Standard sizes are 80 and 119 gallon (usually called 120 gallons). Pressurized water tanks 120 gallons and above are very costly because they require special construction and certification, so it is not uncommon to see locations using multiple tanks connected in series rather than larger tanks...
Solar Water Heater
Solar water heaters use flat panel or tubular solar collectors pointed towards the sun, the collectors have special absorber materials that get hot when exposed to sunlight. Water (or a glycol solution) is pumped through the collectors and circulated back to a tank, repeatedly, slowly heating the water.
Free Hot Water
Some people have pointed out to us that the free
hot water is not free because the HotSpot has a pump
that consumes electricity. HotSpot has an electric
pump, but it uses no net electricity. That’s
because HotSpot lowers the electrical consumption of
the compressor by many times the amount of power its
pump consumes. For example, a five-ton system with
the HotSpot running it will save about 1000 watts at
the compressor while only consuming about 90 watts
at the pump, saving over 900Wh of net electricity every
hour. Plus it makes free hot water ;-)
Return Of Investment is calculated as a percentage
to compare the value of an investment, expressed as
a rate of return. When you invest in energy saving
equipment, and you get to the point where the savings
produced by the equipment has equaled your cost, that
is a full return. How long it takes to get a full return
determines the rate of return. For example, an investment
that returns 100% in one year has a ROI of 100%. If
the full return was after two years, you would have
a 50% ROI. After three years, 33% ROI and so forth.
A payback is calculated as the number of months or
years of energy cost savings are required in order
to return the original investment. For example if the
savings produced were $150 per month and the cost was
$3000, the payback would be 20 months or 1.7 years.