sleepydoc
Team RC
I decided write this thread after reading a lot of misconceptions about power consumption, heat transfer, efficiency, etc in the New EcoTech Marine Vectra Return Pump thread. The information here applies to all pumps (and other aquarium equipment for that matter, since it's basic physics and thermodynamics.)
At the risk of losing some people, I'll start with the first law of thermodynamics: Conservation of Energy. Simply put, energy is neither lost or created. For most of us the only energy we are worried about is the heat in our tanks, but the motion of the water contains and height of the water are also both forms of energy.
Energy is added to the system either by transfer of heat from the surroundings (heat from the room, if it is warmer than the tank, or sunlight,) or from electrical energy from the wall via heaters, pumps and lights.
Energy is lost from the tank either by transferring to the surroundings if the room is cooler than the tank or via evaporation (this actually does the same thing since the water vapor leaves the tank and moves to the room.) Chillers transfer heat from the tank to the room via the coils.
If you tank is too cold, you aren't too concerned with all this. You add a heater which takes xxx watts of electrical energy and converts it to heat in the tank. Life's good.
What most people are concerned about is too much heat in their tank. Then we need to figure out how to remove it, or, better yet, keep it from getting there in the first place.
Ignoring heaters, the two major sources of added heat for most systems are lights and pumps. I won't go into lights in detail, but basically MHs add the most, followed by T5s and LEDs.
Focusing on pumps, while their primary purpose is to move water, they also generate heat. When we talk about how efficient a pump is, what we are really saying is how much extra energy is used or wasted by the pump beyond the energy given to the water by moving it. If we actually calculated this energy and compared that to the actual power consumption of the pump, we could calculate the efficiency, but ultimately, all of this energy becomes heat anyway.
Looking at things in more detail, there are basically 2 types of pumps and 2 configurations: AC and DC pumps, internal/submersed and external configurations. While pumps
To compare them I'll go through the 4 possibilities:
For an internal pump, efficiency is key. Fewer watts consumed means fewer degrees on the thermometer. For internal DC pumps, you have to factor the controller, making things a bit more complex. It is completely possible that two 1000 gph pumps consume 100 watts but one has a 90W motor and a 10W controller, while the other has a 50W motor and a 50W controller. I haven't seen any analysis or comparison on controller power consumption; I assume that they are mostly similar, but I have no data to back that assumption.
For external pumps, the design and efficiency of the cooling system plays a big roll. When someone says a pump 'runs cool,' that could mean that it's an efficient pump that doesn't consume much power, it's got very good cooling an dissipates the heat quickly, or that it's well insulated so all the heat is going into the water rather than to the external casing. Functionally, the best way would probably be to measure temperature of the water going into the pump vs temperature of the water leaving the pump. Unfortunately, most of us don't have that capability and have to rely on empirc data (i.e. how hot our tanks get.)
At the risk of losing some people, I'll start with the first law of thermodynamics: Conservation of Energy. Simply put, energy is neither lost or created. For most of us the only energy we are worried about is the heat in our tanks, but the motion of the water contains and height of the water are also both forms of energy.
Energy is added to the system either by transfer of heat from the surroundings (heat from the room, if it is warmer than the tank, or sunlight,) or from electrical energy from the wall via heaters, pumps and lights.
Energy is lost from the tank either by transferring to the surroundings if the room is cooler than the tank or via evaporation (this actually does the same thing since the water vapor leaves the tank and moves to the room.) Chillers transfer heat from the tank to the room via the coils.
If you tank is too cold, you aren't too concerned with all this. You add a heater which takes xxx watts of electrical energy and converts it to heat in the tank. Life's good.
What most people are concerned about is too much heat in their tank. Then we need to figure out how to remove it, or, better yet, keep it from getting there in the first place.
Ignoring heaters, the two major sources of added heat for most systems are lights and pumps. I won't go into lights in detail, but basically MHs add the most, followed by T5s and LEDs.
Focusing on pumps, while their primary purpose is to move water, they also generate heat. When we talk about how efficient a pump is, what we are really saying is how much extra energy is used or wasted by the pump beyond the energy given to the water by moving it. If we actually calculated this energy and compared that to the actual power consumption of the pump, we could calculate the efficiency, but ultimately, all of this energy becomes heat anyway.
Looking at things in more detail, there are basically 2 types of pumps and 2 configurations: AC and DC pumps, internal/submersed and external configurations. While pumps
To compare them I'll go through the 4 possibilities:
- Internal AC pump - this is easy to figure out. If the pump consumes 50 watts of power, it is adding 50 watts to your tank. It is functionally the same as having a 50 watt heater on. I see people talk about pumps being more efficient or dissipating heat better and 'running cool.' For an internal pump this doesn't matter - all of the energy goes into the water.
- Internal DC pump - this is a little more complicated since it has a controller. The total power consumed by the pump will be that used by the motor plus that used by the controller (TP=MP+CP). The power consumed by the motor is all transferred to the water. The power consumed by the controller is transferred to the air, which may add slightly to the tank, but for our purposes I'll ignore that.
- External AC pump - this gets a little more complicated. The power used (=heat generated) by these is dissipated in two ways. As the motor heats up the heat is either transferred to the water running through the pump, or to the air surrounding it. Now we have two concerns - first the overall efficiency, and second, how much of that power is transferred to the water vs the surrounding air. If you have an efficient 100W pump that transfers 50% of the power to the water, that's functionally the same as an inefficient 200W pump that only transfers 25% to the water, assuming your air conditioning keeps the room cool.
- External DC pump - This simply combines #2 & 3. The heat energy added to the water is simply that consumed by the motor minus that dissipated in the air.
For an internal pump, efficiency is key. Fewer watts consumed means fewer degrees on the thermometer. For internal DC pumps, you have to factor the controller, making things a bit more complex. It is completely possible that two 1000 gph pumps consume 100 watts but one has a 90W motor and a 10W controller, while the other has a 50W motor and a 50W controller. I haven't seen any analysis or comparison on controller power consumption; I assume that they are mostly similar, but I have no data to back that assumption.
For external pumps, the design and efficiency of the cooling system plays a big roll. When someone says a pump 'runs cool,' that could mean that it's an efficient pump that doesn't consume much power, it's got very good cooling an dissipates the heat quickly, or that it's well insulated so all the heat is going into the water rather than to the external casing. Functionally, the best way would probably be to measure temperature of the water going into the pump vs temperature of the water leaving the pump. Unfortunately, most of us don't have that capability and have to rely on empirc data (i.e. how hot our tanks get.)
