Checkthisout
Solar Wizard
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Unless there are bees and mosquitoes.
Heating watts vs cooling watts
- Thread starter 1201
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Unless there are bees and mosquitoes.
With respect, I question this for a heat pump rated to -13F, at 20F. Unless your baseboard heat is cheaper because you use it to heat a smaller area, or you have something at play such as duct leaks in a ducted heat pump situation, I'd suggest you take a closer look at the actual energy being consumed in both scenarios. Electric baseboards are 100% efficient, but heat pumps normally exceed that even down to their lowest rated temperature. So, measured strictly on the cost to supply the necessary BTUs, the heat pump will usually win.
The US Dept of Energy used to supply a spreadsheet calculator that allowed one to compare heat sources using a wide range of fuels, system efficiencies, etc. I probably still have a copy somewhere but will also see if I can find that online to get the newest version, although it probably won't happen this weekend (too many projects to finish before it gets cooler and rainier here tomorrow). Bottom line: Other than cord wood or geothermal (another type of heat pump) it's actually hard to beat an air-sourced heat pump for efficiency, even for heating. I also feel the pain every winter, when our heat pumps are working much harder than when providing cooling. But it would usually hurt even more with another source of heat.
Whats-n-Watts
New Member
Btu's for heat are not the same for air. Heat capacity is typically gauged in kw where air conditioning is gauged by btu. Heat btu from my understanding is a combination of Heat capacity as well as the amount of air displacement the fan is capable of. 1200, 1600, 2000 cfm has much to do with Heat btu's. Heat from any direct electrical source requires more juice. A 1,500 watt space heater for a 150 sqft area only requires an air conditioner that uses around 475 to 500- watts. Big difference. It's harder to heat things than to cool them.
Well… not exactly.
Heat is heat… if the region you live in uses btu for cooling it also uses it for heating… some appliances list the watts instead of the btu, but that is an appliance rating… heat is heat… it’s all a deltaT
It is FAR harder to cool areas than to heat them, because cooling also requires condensing humidity out of the air, and that process also consumes energy, about 3 times as much as cooling non humid air. The reason it SEEMS to be harder to heat than to cool is because of the HUGE delta T required for human comfort in the heating season. -10F to +70F is 80F delta T. 100 to 130F in extreme hot areas Down to 70F is a deltaT of 30to60 F… and getting a heat pump to raise the discharge air temp above outdoor ambient for the ambient to cool and condense the refrigerant for discharge becomes challenging.
Partimewages
Solar Addict
There is no difference between heating watts and cooling watts. A watt is a watt. The difference is in the design of the machine. You can design a machine to be more efficient in heating than cooling or vice versa. Mini splits were developed initially for the cooling environment, hence most are a more efficient cooling machine.
As was stated earlier all of these are heat pumps. A heat pump is a machine that moves heat from one place to another place. Refrigerator, air conditioner, freezer, etc. Each machine can be used in its optimal design condition which will be published in its specifications sheet. From there you will install it in your environment.
You should do a heating load calculation for your peticular load and location. This will determine the size needed and how efficient the equipment will be. For example I am in Central Ohio. Our loads are much different than Central Florida. We spend 98% of our heating load above 17F and we use 75% of our total watts for this peticular equipment in heating. Someone in Florida would not choose the same equipment as myself.
SEER, EER, COP are all markers for being able to compare equipment but if you don't look at the design criteria you may purchase a high efficiency unit for the wrong application.
As was stated earlier all of these are heat pumps. A heat pump is a machine that moves heat from one place to another place. Refrigerator, air conditioner, freezer, etc. Each machine can be used in its optimal design condition which will be published in its specifications sheet. From there you will install it in your environment.
You should do a heating load calculation for your peticular load and location. This will determine the size needed and how efficient the equipment will be. For example I am in Central Ohio. Our loads are much different than Central Florida. We spend 98% of our heating load above 17F and we use 75% of our total watts for this peticular equipment in heating. Someone in Florida would not choose the same equipment as myself.
SEER, EER, COP are all markers for being able to compare equipment but if you don't look at the design criteria you may purchase a high efficiency unit for the wrong application.
tomy2
escape artist
simply put, the outside unit does all the work in cooling phase, and the inside unit does all the work in heating mode.
timselectric
If I can do it, you can do it.
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All of the work is done in the outside unit, for both modes. That is where the compressor is. And all of the electric controls.
The inside unit is just a fan coil.
These systems are designed for efficiency in cooling mode. But when the two coils are used in the opposite order, they can be used for heating.
Just not as efficiently.
Partimewages
Solar Addict
I did geothermal (Ground Source) for a number of years. One of the equipment manufacturers used a compressor system that was in the air stream specifically because it add heating watts/BTUs to the heating capacity of the equipment. These machines could achieve between 3.5 and 4.0 COPs with 50F Ground water. They were still higher capacity cooling units than heating.
tomy2
escape artist
I am currently looking for second mini-split to heat my house better. I've been fixated on seer #, but after this conversation , I think that one with a larger indoor unit [18btu] and lower seer [19], might be more efficient than a smaller unit [9kbtu] with a 25 seer rating, at least for heating.
I know that seer applies to cooling, and the EER on both units is often about the same.
Checkthisout
Solar Wizard
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Trying to heat the interior in the winter is akin to trying to drop the interior temp of the house below say 60 in the summer.
You have to run the compressor faster in order to keep the refrigerant pressure lower on the cold side so evaporation can take place.
Also need higher fan speeds to keep evaporator efficiency up.
This is why ground-source heat pumps are the bees knees.
You have to run the compressor faster in order to keep the refrigerant pressure lower on the cold side so evaporation can take place.
Also need higher fan speeds to keep evaporator efficiency up.
This is why ground-source heat pumps are the bees knees.
tomy2
escape artist
apparently too simply put. but doesn't the size of the indoor coil determine the heat output?
timselectric
If I can do it, you can do it.
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Coil size absolutely plays a major part in it.
Well, the coil size determines the hx transfer size to airflow ratio.
A certain coil surface area is required per btu of heat transfer.
Airflow statistics over delta t and compressor ratio determine heat transfer ability and efficiency.
It's a mad dash between goals.
Partimewages
Solar Addict
tomy2
escape artist
by ground source do you mean geothermal ?
Bob in Tucson
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Sizing and efficiency are two different things. As @Partimewages suggested, you should do a load calculation (Manual J) to determine the size of the unit required to meet the design conditions for your space. Once you have that value you can choose whichever model you want so long as it's the target size; one criterion to consider is SEER (now revised to SEER2).
Partimewages
Solar Addict
Yes
Zwy
Emperor Of Solar
People do not understand, heat moves to cold. With a high delta T when heating, there isn't much heat energy available in outside ambient temps to move to the refrigerant.
Checkthisout
Solar Wizard
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No.
I mean hvac systems where the outside coil gets/sheds it's thermal energy from water circulated in pipes that are buried in the ground.
Bonus points if it's winter and you happen to have hot spring or lava very close to the surface.
In that case you can just pump the water straight through your towel warmer and toilet seat heater.
Partimewages
Solar Addict
In North America ground source is commonly known as "Geothermal"
Ground source heat pump
Geothermal
Ground coupled heat pump
Open loop water source heat pump
Closed loop water source heat pump
There is very little true hot water in the ground in North America.
Ground source heat pump
Geothermal
Ground coupled heat pump
Open loop water source heat pump
Closed loop water source heat pump
There is very little true hot water in the ground in North America.
