MarvelAtTheSky t1_j827tbz wrote

Yeah, I do Ground Source Heat Pump calculations too. All Air Source Heat Pumps such as those on these water heaters require a large volume of constantly heated air that above their ‘Balance Point’. Because of such a small fan on the water heaters the balance point is pretty high at 50-60, but you don’t want it to operate at the balance point, it’s least efficient there as at that point it’s COP 1 or at 100% parity to resistance heat. You would want a heat source that is hotter to get the rated efficiency otherwise the compressor runs progressively harder to extract enough heat.

1kw = 3412 BTU, it takes 1 BTU to raise 1lb of water 1° F, 1 gallon of water roughly weights 8.33lbs. So, 8.33x50Gallons = 416.5 lbs of water x 73° rise to get to 120°F tap temp = 30404.5 BTU / 3412 BTU = 8.9kW input total the interval depends on the wattage rating of the water heater and usually is presented as a recovery time. But 30404.5 BTU needed, that is a lot of heat. Ground source heat pumps require acres and acres of tubing to collect that much heat and their COP is very high at like a 5 or more, water heaters are only a 2.2ish. So the house’s basement would have to be hundreds of feet deep or have a large footprint to collect that much heat or loose 30404.5 BTU on a consistent basis to be totally free of the water heater using the resistance coil. Unless the heat comes from the atmosphere outdoors it’s costing you something, somewhere to move into your space. Newer, REScheck compliant houses loose around 21000 BTU per hour, so at 30404 to totally negate the need for the water heater to not use the ‘backup’ resistance coil. Your furnace would be chugging hard produce those BTU’s and that energy use issn’t required to be on the Energy Star label and is what is costing you money in whatever fuel source it uses.


MarvelAtTheSky t1_j81w0lw wrote

I appreciate your well done calculations. The only missing link is the heat energy heat pump water heaters collect is costing money from another source in colder climates, such as ours. The BTU’s taken in are collected from that generated by our heating systems in all but a few months of the year. While these do lower the electricity used by the unit themselves, unless the place they are located has excess heat such as, for example, that from a greenhouse that experiences solar heat gain, they are making another system in our homes run harder or longer to generate the heat they are collecting. Heat Pump HVAC systems benefit from being able to move very large amounts of air in the outdoors so they represent huge savings now since newer versions can overcome their balance points at very low temperatures, but in northern areas the balance points of tanked heat pump water heaters can only be overcome by being in our heated spaces indoors and those spaces need to have a high volume of air available for their fans to move enough air to collect heat from to not need the electric element.


MarvelAtTheSky t1_j81u4x8 wrote

So, your electric bill is lower, but if it is collecting that much heat in your basement enough to overcome its balance point on a consistent enough run rate to save ‘big bucks’, where is the heat energy coming from that gets to the basement for it to extract when it’s 30 degrees outside?

Your floors are providing the heat via your furnace heating the house. If you read my post I’m not giving hard numbers or saying they don’t have a use case, but the movement of heat energy is very complicated, so much so my work is done for the Department of Energy, ASHREA and ACCA and is only accepted when it’s corroborated with three other engineers work. If your loosing that much heat energy from the buildings thermal envelope, your biggest savings are insulating your house, in which case once you would, your heat pump water heater that has a high balance point of close to 50° would end up running almost entirely on its electric element.


MarvelAtTheSky t1_j817pxy wrote

I do home design including Manual J / efficiency calculations as one of my many jobs. My recommendation on a heat pump tanked water heater is really consider if where it needs to be placed has excess/unwanted heat and very good airflow to were the heat comes from.

A heat pump works by pulling heat energy out of the air, which requires another source, usually a furnace in norther climates, to provide more BTU’s to replace it. In the Summer this helps your A/C, but since there is lower heat available in the space it will use its standard ‘backup’ electric resistance heating element, making it into a just standard electric water heater. Also the majority of the heat pumps on tanked heat pump water heaters don’t last very long, only 10 years at most, which is how long many tanked water heaters last anyway, depending on water quality. So even with tax credits and rebates, is there going to really be a return on investment for the heat pump water heater. Heat pump tankless waters make a lot of sense in southern states because they can just go in a garage or outdoor closet and the more moderate climate affords then ample heat energy from the outdoors all year long without the threat of freezing or needing more ambient air heat, but in PA, they are rarely a good investment.


MarvelAtTheSky t1_j6sgxyx wrote

I agree the police are not ideal, this requires a new position that is a hybrid response of someone trained in mental health and first deescalation. A key aspect that is often overlooked is situational assessment to know how to respond. My ex is a psychologist and many times said they would definitely not be effective to be sent by 911 into a mental health situation that has deteriorated into a dangerous situation because the ability to know how to prevent further escalation involves an understanding of the cause to know how to interact with that person first, an almost impossible task without that person seeking help beforehand. Introspection is extremely difficult because we are all different and there is no benchmark of perfect mental health to constantly compare ourselves to and when a mental health crisis has elevated to the point of the it effecting others in negative ways and in most cases someone directly involved not being able to be aware they need help or who to even call, 911 is the universally known place to call for help me is often called by someone who is not the person who needs the help themselves. A new mental health offering needs to be added to emergency services to go along with the fire, police and medical offerings that are currently the standard. But this is a step towards that, since such trained personnel are not yet available.


MarvelAtTheSky t1_j6qf53a wrote

This is a thoughtful and logical step to take that other areas should really follow. A friend of mine is a state police officer in Virginia and has first hand experienced situations were mental health expertise was the real necessity and not just someone with full mental capacity committing an act that violates the laws, like they are trained to handle.