EcoRenovator - View Single Post - Thermal storage and water to water heat pump

jeff5may · 05-22-17, 01:04 PM

While 3.5 million BTU's sounds like a lot of heat, it's really not. The average single family home consumes between 90 and 120 million BTU's a year. So without any heat input, your cistern only has enough (sensible) heat capacity for around 2 weeks of average heating or cooling. We all know that heating and cooling need is not average in nature.

What will happen with a system like this? You will have a week or so of low hanging fruit, when it is very economical to move heat into or out of the cistern. After that, either the heat pump will win or the heat flow will win. You will reach a state of equilibrium where it is cheaper to use outdoor air (unless it is below freezing outdoors and you try to freeze the cistern) to move heat with. Unless you increase the surface exchange area somehow, you have a few million BTU's of window to operate in; after that, heat (or cool) costs extra.

05-22-17, 01:04 PM	#4
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	While 3.5 million BTU's sounds like a lot of heat, it's really not. The average single family home consumes between 90 and 120 million BTU's a year. So without any heat input, your cistern only has enough (sensible) heat capacity for around 2 weeks of average heating or cooling. We all know that heating and cooling need is not average in nature. What will happen with a system like this? You will have a week or so of low hanging fruit, when it is very economical to move heat into or out of the cistern. After that, either the heat pump will win or the heat flow will win. You will reach a state of equilibrium where it is cheaper to use outdoor air (unless it is below freezing outdoors and you try to freeze the cistern) to move heat with. Unless you increase the surface exchange area somehow, you have a few million BTU's of window to operate in; after that, heat (or cool) costs extra. Last edited by jeff5may; 05-23-17 at 10:00 PM..