Your favorite energy geek's newest toy

[Mikey]

Just completed installation of a hybrid heat pump electric water heater.

What, you might ask, is a hybrid heat pump electric water heater? It uses a heat pump (like your air conditioner) to heat the water, instead of a gas burner or electric resistance element. The heat pump has a UEF (Uniform Energy Factor - a measure of efficiency) of 3.75. Gas water heaters are generally between 0.5 and 0.7, conventional electric resistance water heaters are from 0.75 to 0.95. So, the heat pump has an efficiency 4 times the conventional electric water heater and up to 7 or 8 times that of a gas water heater (we replaced a propane unit, which is similar).

It also blows cool air into the garage. So this is really acting like a small AC unit, where it removes heat from the air and adds it to the water instead of blowing the heat outdoors through the condensing unit (which is what an air conditioner does). It's "hybrid" because the heat pump loses its efficiency below about 37 deg F, so it has a conventional heating element to take over when it gets really cold (which it rarely does here).






It also has WiFi capability so I can control it from an app on my phone.




I can schedule it to raise or lower the setpoint (or even turn it off) during periods of high electric rates or when away from home. After I screw around with it for a while I might just turn it off from 4:00 pm until 9:00 pm when our rates are extremely high. It should have enough water in its 50 gallon tank to get us through that period without heating at all.




It will even tell me how much electricity it's using.

[Mikey]

With this, we have finally replaced all of our propane appliances. I will take great pleasure in calling Amerigas today to tell them to come and get their tank. No more $4.00 per gallon propane, and no more 300 gallon propane bomb sitting 10 feet from the side of our garage. Everything now works on electricity, which I'm producing with my magic shade tree and some additional panels on the roof.

[Bill in Houston]

How many months until your cost break even on the investment?

[Mikey]

How many months until your cost break even on the investment?

Haven't figured that out yet, but it will probably be several years because it wasn't a cheap install. Equipment plus installation (including removal of the old tank) was over $3,000. I have a workbook buried somewhere on my computer where I worked it all out (sort of) last year, and I just need to go and put in the final numbers. I should be saving something like 80% on the cost of heating water.

It's not just that though. We don't have natural gas service here, so we've been using propane since we moved in 20 years ago. We started out with propane water heat, space heat, and clothes dryer. Even a propane pool heater which I ran a couple of times before I realized that it was too expensive to use. The 320 gallon tank is located about 10 feet from our house, right next to our main electric panel. It would not be to code today and we consider it a fire hazard with the increasing incidence of wild fires here in SoCal. We replaced our dryer with a new heat pump model last year and also completely replaced our HVAC with an ultra high efficiency zoned heat pump system. So, the water heater is the last to go.

It's actually pretty complicated, but it could work out that I'm operating all these electric appliances for "free", because I have 7.5 kW of PV capacity and a storage battery that allows me to "arbitrage" our time of use electric rates. We added the last 2.5 kW last November and we are way overproducing right now, especially considering that I'm not commuting every day in my EV. Building up credits on my electric bill which I will use during the winter when solar production falls off. With all this new equipment interacting with the time of use rates ($0.52/kWh from 4:00 pm until 9:00 pm in the summer but only $0.09 between midnight and 6:00 am) I just need to see how everything meshes over the next 9 months or so. The cost effectiveness of any single piece can't really be separated from the whole system.

[Screw_Michigan]

Is it a hot water heater?

[Mikey]

Actually it's a cold water heater. You don't need to heat hot water.

[Screw_Michigan]

Actually it's a cold water heater. You don't need to heat hot water.

I know. I was channeling on that one.

[Mikey]

Yeah it's a Rheem.

TBH I'm not sure how the ambient temperature affects the performance. Whether it slows it down or just decreases the efficiency. I'm sure that there are some standard set of conditions that they are tested at.

The standard rating criteria are a little hard to follow.

The first hour rating is 67 GPH which, I think, means that it can produce 67 GPH if you start out with a full tank of water at the setpoint temperature, without reducing the tank temperature by more than 15 deg (or something like that).

Then there's the "recovery in GPH at 90 deg F rise" which, I think, means that if you start out with cold water it can raise 27 GPH by 90 deg. So that would be about 2 hours for a 50 gallon tank. Our inlet water temp is probably more like 60 deg (maybe higher) in the summer so we don't need a 90 deg rise.

https://s3.amazonaws.com/WebPartners/Pr ... DC11B3.pdf.

It's supposed to work down to 37 deg F, which is when the resistance heating element kicks in.

[Mikey]

Part of all this energy stuff, besides being in my wheelhouse, is that the wife is retired and I want to retire within the next couple of years. We don't want to move from here if we can still maintain the house. One of my goals is to zero out our utility bills, or at least minimize them to the greatest extent possible. I think I'm there now for energy. We will always have to pay our water bills, though. Will probably cut the cable sometime in the near future and just go with the interwebs.

[Mikey]

This is kind of interesting. At least to me.

Yesterday's profile, in 15 minute intervals. This is with the electric water heater working and a fair amount of AC running in the afternoon and evening.



The dark blue costs me $0.52/kWh when it's positive, but pays me $0.52 when it's negative.
The lighter blue is $0.24/kWh and the light green (or whatever) is $0.09/kWh.

The negative areas are when my PV is producing more than I'm using. The positive areas are when I'm using more than the PV produces.

The storage battery discharges from 4:00 pm (during the expensive period) until midnight if the PV isn't covering my usage. Notice that it's either negative or only slightly positive until about 10:00 pm when it's down to its minimum state of charge.

At midnight the battery starts charging at $0.09/kWh. All that usage would have been in the expensive period without the battery.

Net for the day, I used a total of 1.4 kWh but gained a credit of $3.10 because of the time of use difference.

So far, for the current billing period (since 7/22), I've used negative 94 kWh and have gained a credit of $76.00.

[Mikey]

How much did it cost for the equipment and installation?

It's complicated. But off the top of my head...

We installed 5 kW of PV in 2012. it cost about $40,000 at the time but we got a 30% tax credit. Also, it was mounted on a shade structure over our patio that we really needed, and the cost of the structure was rolled into the total system cost for the tax credit. Value of the shade structure was probably $15,000. So I'll say net $10,000 for the PV, which has been producing free electricity for 8 years.

Added another 2.5 kW of PV last year with a net cost of about $6,000.

We changed out our HVAC system last year. It was an old system with SEER 13 and propane heat, replaced with a high efficiency multi zone heat pump system (SEER 24). It will probably save us 75% on cooling energy and 80% to 90% on heating (propane is very expensive). This conversion was $30,000 (ouch) but with rebates from Home Depot and a really dumb mistake by a credit card company our net cost was about $12,000.

The storage battery had a net cost of about $10,000 installed. the water heater about $2,500.

Add it all up it looks pretty expensive, about $40,000 total.

We were paying probably between $250 to $500 per month, depending on the time of year, for electric 10 years ago and probably $2,500 to $3,000 per year for propane.

That is all gone now. Plus I'm charging my EV for free and hopefully will never have to pay for electricity, propane or gasoline. I also have backup power from the PV and battery in case of a power failure. This is part of my long term retirement plan.

[Bill in Houston]

I was not told there would be math involved

[smackaholic]

Actually it's a cold water heater. You don't need to heat hot water.

I know. I was channeling on that one.

I'll admit to going to the "you don't heat hot water" card on occasion. I'm sure dins makes good use of it.

[smackaholic]

Congrats on the energy weenie score. Those things are pretty much a no brainer in your neck of the woods.

I am a bit surprised that a fat fuck gourmet like you would give up the superior cooking capabilities of gas to save a few bucks. Do you at least have a propane burner on the grill for those times when you really do need a flame to cook? I have a wok I haven't used in decades because it just doesn't work worth a damn on an electric element, especially a glass cooktop.

[Kierland]

I was not told there would be math involved

In a Mikey thread about energy? Yeah don’t make that mistake again.

[Mikey]

Never had gas cooking here. The house had an all electric kitchen from day 1. We thought about extending the propane into the kitchen when we moved in but it wasn’t really too feasible.

And yeah I do have a big gas grill outside along with a charcoal smoker/grill.

I’ve wanted to get rid of the propane for years. I pay (paid) over $4.00 per gallon for a minimum 100 gallon delivery. I can get my five gallon grill tank for less per gallon than that.