Heat pump water heaters

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

We pay 21 cents total per kwh for electric in Maryland. Not sure what our natural gas costs are. Heat pumps don't always operate at max efficiency.

On the website below the current price for MD is listed as 17 cents:

https://www.eia.gov/state/data.php?sid=MD

Tell that to my pepco bill lol

There might be a variety of charges on the bill above and beyond the hourly rate. To compare electricity vs gas unit prices, we need to treat those charges symmetrically, so that we don't inadvertently bias the results. Probably, 17 cents is indeed the unit rate for electricity if you strip away the various extra charges.

All the "extra charges" except an $8 customer charge are based on the amount of electricity we used so yes, they are relevant for comparing costs. One of those for example is the Montgomery County energy tax which is a little over 1 cent per kwh. The rates also seem to change - there are summer rates and winter rates for example. If you take out the $8 customer charge, 20 cents is our average over the last 6 months.

The main reason we won't be getting a heat pump water heater is because it would cool our basement in the winter. We do have an air source heat pump as part of our HVAC system.

My point is that there are also extra charges on one's gas bill. So we shouldn't ignore the extra charges on a gas bill and include them on an electrical bill. We should use a symmetric approach so that the resulting unit costs are apples to apples.

It doesn't seem to me that we should ignore any of the "extra charges" that are based on the amount of electricity/gas used. Ignoring them means you're not accounting for the full costs of either and therefore you aren't doing a useful comparison at all.

I'm not saying you should ignore them. I'm saying that you must aim for an apples-to-apples comparison of the unit price of electricity and the unit price of gas. Including extra costs on the electricity side of the ledger, but excluding them for natural gas, would be a mistake. So go ahead and include the extra charges in your calculations, but include them both for electricity and for natural gas.

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

We pay 21 cents total per kwh for electric in Maryland. Not sure what our natural gas costs are. Heat pumps don't always operate at max efficiency.

On the website below the current price for MD is listed as 17 cents:

https://www.eia.gov/state/data.php?sid=MD

Tell that to my pepco bill lol

There might be a variety of charges on the bill above and beyond the hourly rate. To compare electricity vs gas unit prices, we need to treat those charges symmetrically, so that we don't inadvertently bias the results. Probably, 17 cents is indeed the unit rate for electricity if you strip away the various extra charges.

All the "extra charges" except an $8 customer charge are based on the amount of electricity we used so yes, they are relevant for comparing costs. One of those for example is the Montgomery County energy tax which is a little over 1 cent per kwh. The rates also seem to change - there are summer rates and winter rates for example. If you take out the $8 customer charge, 20 cents is our average over the last 6 months.

The main reason we won't be getting a heat pump water heater is because it would cool our basement in the winter. We do have an air source heat pump as part of our HVAC system.

My point is that there are also extra charges on one's gas bill. So we shouldn't ignore the extra charges on a gas bill and include them on an electrical bill. We should use a symmetric approach so that the resulting unit costs are apples to apples.

It doesn't seem to me that we should ignore any of the "extra charges" that are based on the amount of electricity/gas used. Ignoring them means you're not accounting for the full costs of either and therefore you aren't doing a useful comparison at all.

I'm not saying you should ignore them. I'm saying that you must aim for an apples-to-apples comparison of the unit price of electricity and the unit price of gas. Including extra costs on the electricity side of the ledger, but excluding them for natural gas, would be a mistake. So go ahead and include the extra charges in your calculations, but include them both for electricity and for natural gas.

Okay captain obvious, I'll be sure to do that. I don't know how the costs are in VA but in our bills, not including them for both makes electricity look less expensive than it actually is, while it has a minimal effect on natural gas.

[Anonymous]

Anonymous wrote:

You don’t even understand enough about thermodynamics to know what you don’t know.

And you think I’m the stupid one!

You went to an Ivy and have two MA’s, don’t you?

The confusing point for many people is the idea that an efficiency metric can exceed 100%. Intuitively, it seems like 100% should be the limit. In the case of a heat pump, that is not the case. The key point is that a heat pump isn't creating heat; rather, it is moving heat from outdoors to indoors. If we can use one unit of energy to move two units of heat into our home, then we have achieved 200% efficiency.

No, you haven’t.

[Anonymous]

Anonymous wrote:

Anonymous wrote:

You don’t even understand enough about thermodynamics to know what you don’t know.

And you think I’m the stupid one!

You went to an Ivy and have two MA’s, don’t you?

The confusing point for many people is the idea that an efficiency metric can exceed 100%. Intuitively, it seems like 100% should be the limit. In the case of a heat pump, that is not the case. The key point is that a heat pump isn't creating heat; rather, it is moving heat from outdoors to indoors. If we can use one unit of energy to move two units of heat into our home, then we have achieved 200% efficiency.

No, you haven’t.

OK, to be more precise: the "coefficient of performance" is 200%.