Comment by smooc | Hacker News Reader

Comment by smooc | Hacker News Reader

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Where do you get your numbers from? Right now, pre heat pump, I'm at 2000kWh usage and return to the net 4000kWh (so 2000kWh in excess). I use 750m3 of gas.

This costs me 100e per month.

I'm investing in a full electric ground source heat pump. Which cost me 20k. An alternative is a air heatpump which is around 8k, but with a lower scop.

Let's assume a scop of 5 (air-air) which is conservative. The amount of energy required for heating / showering / cooking was 750 * 9.27 = 6952.5 kWh. Dividing this by the scop of 5 means I require 1390.5 kWh to replace gas. This means I still have excess of solar kWh.

For now I can use the grid as a battery. This means I have no electricity costs - I actually get 20e per month after taxes.

So for 8k I have nullified my gas and electric bill. This means a payback period of 5.5 years (8000/120/12) or a yield of 18% (120/8000 * 100*12) per year.

So it isn't required to have tens of thousands to invest and you get a positive yield (depending the tax climate) even with current gas prices.

The 20k ground source heat pump looks a bit different. But I like that it is quiet and it can cool in summer for less energy that an air-air one.*

While heat pumps tend to pay themselves back by simply being one of the most efficient methods of heating possible, they do require a large investment upfront. With the current economic situation, it makes sense that fewer people are willing to make such an investment. You could of course get a loan, but not everyone is interested in getting themselves into any kind of financial risk when cost of living is up and wages are lagging behind.

ROI depends heavily on the amount of solar power you can also invest into, the weather, and fossil fuel prices. Right when fossil fuel prices spiked because of Russia's invasion, getting a heat pump was a no brainer, because the difference between electricity and fossil fuel prices took months or more off the time to earn back the heat pump investment, but now that fuel prices are dropping back to normal, the equation changed.

Of course. But if you can make the investment then the yield is more important to compare it against other investments.

The problem is that an outdated inefficient Rankine Refrigerant Heat controls 99% of the market and in extreme climate temperatures (High Delta Ts) the Rankine COP efficiencies are 0-1 in the example of - or + 10-20C , virtually useless and use excess Kwh. The HVAC OEMs are about the slowest good ole boys to adapt or innovate. Our co, Sencera (sincere.com) is mfg the 1st Stirling Heat Pump that replaces Rankine Refrig Heat Pumps @same and delivers 30% HIGHER COP efficiency over Rankine Heat Pumps and is performs even better in extreme cold/hot climates. Trust and used by NASA Stirling was previously known as super expensive and used in the RPS systems in the Space shuttles. We reconfigured Stirling to be low cost ($600 mfg cost 3 Tom/10Kwh Units) with a Patented all Rotary design and utilize Helium or Nitrogen(NON toxic and NON flammable) with working prototypes with independent lab verified COP efficiencies HIGHER than Rankine. In 2024 you'll see the comm'l entry of our 1st Home Units then we scale to EVs and Comm'l Cold Chain apps. Since 100% of every Rankine Heat Pump leaks in all Homes, Schools, Hospitals and Businesses and depends on Refrigerants, the lazy HVC market's new spin is "sustainable" Refrigerants, such B.S, they contain harmful CFC/HFCs or in Europe you have R-290, a Propane derivative, try lighting a match next to it and see what happens:). The Industry is so old and apathetic it's going to see a refreshing disruptive change maker in Stirling as an end user option that can serve Colder/otter climates and significantly reduce Kwh/Utility Bills. mike.draper@sencera.com

BTW, when Daikin or Carrier or anyothers sell their Heat Humps at COPs of 5 based on a SEER Rating, you can laugh....it's a blended rate and represent ZERO integrity to the actual Heat Pump performance in extreme temps....how did this happen? ASHRAE , SEER Rating are all sponsored and created by WHO? The HVAC good ole boys....so they are blatantly overselling HYPED COP efficiency that are actually 25% of their real COP....we've tested Daikin the highest selling Home Heat Pump units in Spain lab and the results were clear at -20C the COP was 1.25 but SEER Rating star it's 5. If the general public only kew the facts :)

How would the sums work out if you were actually paying for electricity?

Good question. It depends on how that would work. Meaning can I offset against the whole year and just get less money back per kWh or will it become seasonal or day pricing. Day pricing would be the most impactful as during summer time prices are cheaper and I deliver back the most.

If I assume that 2/3 of my usage will be in Winter and I can offset just 200kWh (there is always a bit of sun) then it look like this:

1390.5 * 2/3 = 927 kWh 927kWh - 200 = 727 kWh 727 kWh * 0.40 = 290.80 / year (0.40 is price per kWh)

So I would spend 290 per year so about 25e. Which is 75% less then I do now.

This excludes any other cost / benefit.

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