Natural Gas vs Heat pumps for heating

[wwhitney]

The 20F temperature drop was the new construction guideline for Sacramento county at the time. It was to be measured at 5' above the floor. The builder sent me a copy because I thought it was BS.

OK, so the guideline was a bad design. A proper Manual J would have given you a system that provided a 30F or 35F temperature differential at full tilt. I.e. the problem is with the guideline, not with "right-sizing."

Cheers, Wayne

 

[RKCRLR]

OK, so the guideline was a bad design. A proper Manual J would have given you a system that provided a 30F or 35F temperature differential at full tilt. I.e. the problem as with the guideline, not with "right-sizing."

Cheers, Wayne

Oh, I agree the guideline was bad, but that is what I had to live with. As did all my neighbors in the housing tract. That's why I put "oversized" in quotes. My current system is oversized to that bogus guideline and the whole experience made me wary about about government requirements regarding sizing.

I was responding to the comment about right-sizing and set-back temperatures. My current system was sized using the Manual J requirements. But that doesn't mean because I can use temperature set-backs on more moderate days that my system isn't right-sized. I just wish the system was smarter about recovering from set-backs during the extreme days.

 

[holeydonut]

Several people I know, myself included, put solar panels on the roof AND THE GROUND, so actually a lot more could put in more panels if they used ground mounted panels. They look nice along the fence and make more shade for the groundhogs. I mean dogs. My relative in WA put his 5' off the ground and claims he can brush the snow off easier there. It seems interesting that people worry about using some NG, especially in the winter. Do what you can. Eventually add batteries and use less NG. The gas company doesn't require a minimum use here, at least, but I'm sure we use that much if they did.

California has the second smallest average detached home lot in the USA. Ground mount solar in California is a dream to be had by a lucky few. TMC users probably tend to have more wealth, so it seems lots of people here have mega acres and mega roof planes to be able to generate mega solar. But I don't think the average home can overproduce the way we'd all want.


PS, I'd love me some ground mount solar.

 

[sorka]

I believe that information is out of date. Heat pumps can certainly work when the 99% design temperature is below freezing, certainly down to 17F, maybe lower.

Cheers, Wayne

Totally agree. I was just saying that they may not be the most awesome choice if you live in climates where the temperature is below freezing a lot if you're trying to compare efficiency with using NG directly for carbon footprint purposes.

 

[sorka]

Admittedly, I'm a little prejudiced towards "oversizing" a system. My first new home in Sacramento had AC sized per the rules. My first summer in the house sometimes the outside temperatures were 110F or higher. MY AC was running continuously and it was 90F inside. I called the warranty department and was told that the AC was sized for a 20F temperature drop from the outside temperature and that the system was working properly. I swore never again.

But, as I remember, my hybrid system size was driven by the heat pump operation. When I first moved in my wife and I were only home 12 hours a day (if that). It made no sense to maintain the inside temperature during moderate temperature days that the system could easily recover from a set-back temperature. It's only during the extreme days that the system needs to run constantly to maintain the temperature. But my smart thermostat (which is rather advanced) doesn't have the option to monitor temperatures and predicted weather forecasts to determine if set-back temperatures need to be bypassed.

Also, because of the required defrost cycles, the heat pump can't run continuously in heating mode (at least mine can't). It basically runs in AC mode during the defrost cycle. So it has to be able to recover from the defrost cycles. It has an option of weather or not to run the furnace during the defrost cycle which I have set to on. Its very uncomfortable during the defrost cycle otherwise and I can't imagine how long it would take to recover if it wasn't used.

When discussing heat pumps, remember that a regular AC system already is a heat pump so when we discuss heat pump HVAC systems that also heat, the main difference is you're now using essentially an AC system in reverse to heat your interior space or heat your water.

 

[sorka]

There's no way I could way I could agree to banning NG/Propane appliances until we have a reliable grid. And the reliable grid would have to come first.

Except that heating your house with NG still requires the grid to be up.

 

[RKCRLR]

When discussing heat pumps, remember that a regular AC system already is a heat pump so when we discuss heat pump HVAC systems that also heat, the main difference is you're now using essentially an AC system in reverse to heat your interior space or heat your water.

Oh, I understand that well. The point I was making was, as I remember in my case, the sizing was driven by the heating load, not the cooling load. And the CoP numbers don't take the defrosting requirements into account (as far as I know).

 

[RKCRLR]

Except that heating your house with NG still requires the grid to be up.

When I was using NG I don't ever remember it going down when the power was out. But I didn't have the power outages then that I do now.
My furnace doesn't require much power to run the fan and controls. A small generator will run it. But it takes a very large generator to run a heat pump.

 

[RKCRLR]

When I was using NG I don't ever remember it going down when the power was out. But I didn't have the power outages then that I do now.
My furnace doesn't require much power to run the fan and controls. A small generator will run it. But it takes a very large generator to run a heat pump. Same with my on-demand water heater vs a hybrid water heater.

 

[holeydonut]

Except that heating your house with NG still requires the grid to be up.

Lolol. This reminded me of the day the PG&E line worker guy disconnected my electricity for my solar+ESS install, but then told everyone on site that if they touched my main service panel, then he wouldn't turn my electricity service back on (PS, did you know I hate PG&E?)

Anyway, when the jerk-o came back to my house 8 hours to turn my electricity back on, I asked him why he thought it would be a good idea to leave my home without electricity in the middle of November since it caused the interior home temperature to plummet since I couldn't run my furnaces. And he said "but your furnace is gas right? you could have run it just fine."

I was so pissed - how in the hell am I supposed to run the air handler if PG&E threatens the people who are working on my house? That if they touch my main panel then I'll never get my power turned back on????? FRACCCKKK YOU PG&E FFFFFFFFFFFFFUUUUUUUUUUUUASDFJALSDJ#@*U

PSS. Did you know i really really really hate PG&E?

 

[mikesm]

When I was using NG I don't ever remember it going down when the power was out. But I didn't have the power outages then that I do now.
My furnace doesn't require much power to run the fan and controls. A small generator will run it. But it takes a very large generator to run a heat pump.

That is a bit of a misleading statement. Variable Refrigerant flow heatpumps allow the use of much smaller generators to support them than traditional units. A traditional compressor based system kicks on at full power, and needs up to 100A to start the compressor and then runs at 40A after that. This is very hard on a generator and needs one with a lot of wattage to support it! In contrast, my Mitsubishi VRF outdoor starts up at 5A, and then cranks up to a max of 35A over time if the delta T is really big ion all the indoor units. It's far easier to run VRF based systems of genset than conventional ones which would have to be much bigger to deal with the 40A max being hit all the time, even if you had soft-start installed on the compressor to soften the 100A cranking at the very start.

 

[RKCRLR]

That is a bit of a misleading statement. Variable Refrigerant flow heatpumps allow the use of much smaller generators to support them than traditional units. A traditional compressor based system kicks on at full power, and needs up to 100A to start the compressor and then runs at 40A after that. This is very hard on a generator and needs one with a lot of wattage to support it! In contrast, my Mitsubishi VRF outdoor starts up at 5A, and then cranks up to a max of 35A over time if the delta T is really big ion all the indoor units. It's far easier to run VRF based systems of genset than conventional ones which would have to be much bigger to deal with the 40A max being hit all the time, even if you had soft-start installed on the compressor to soften the 100A cranking at the very start.

Perhaps saying a very large generator is needed is misleading but it is relative. Regardless of starting current, when the overnight temperatures are in the 20s and the power is out for days at a time I can get by with very little electricity using my propane furnace and tankless water heater. I'd need a lot bigger generator if I was relying on a heat pump and hybrid water heater. My well is the biggest user of electricity and I can manage when it runs.

 

[jjrandorin]

(moderator note)

I am not quite sure what this thread has morphed into. It was posted when I was away from TMC for a few days. It appears to have started off as an energy policy discussion, and morphed into "something else".

Since its active here, I am going to leave it here. With that being said, here is another reminder that TMC is not a place for political discussions, so posts with that slant will be moved.

 

[sorka]

Perhaps saying a very large generator is needed is misleading but it is relative. Regardless of starting current, when the overnight temperatures are in the 20s and the power is out for days at a time I can get by with very little electricity using my propane furnace and tankless water heater. I'd need a lot bigger generator if I was relying on a heat pump and hybrid water heater. My well is the biggest user of electricity and I can manage when it runs.

My well is one of the biggest reasons I got 3 PWs. I could go without heat if necessary but not water.

 

[sorka]

(moderator note)

I am not quite sure what this thread has morphed into. It was posted when I was away from TMC for a few days. It appears to have started off as an energy policy discussion, and morphed into "something else".

Since its active here, I am going to leave it here. With that being said, here is another reminder that TMC is not a place for political discussions, so posts with that slant will be moved.

It morphed easier than typical because the topic I posted was actually in error and the rate I hike I was referring to was because I linked to the wrong tariff file. Maybe we can retitle it?

 

[jjrandorin]

It morphed easier than typical because the topic I posted was actually in error and the rate I hike I was referring to was because I linked to the wrong tariff file. Maybe we can retitle it?

what title would you suggest / like?

 

[h2ofun]

It morphed easier than typical because the topic I posted was actually in error and the rate I hike I was referring to was because I linked to the wrong tariff file. Maybe we can retitle it?

should the entire thread be deleted?

 

[jjrandorin]

should the entire thread be deleted?

In my opinion, no, as we very (very very) rarely delete a thread with this much activity in it.

 

[bmah]

should the entire thread be deleted?

I'd say keep it...there's some interesting discussion in here, although I'm not sure what title could accurately describe this thread.

Bruce.

 

[holeydonut]

what title would you suggest / like?

Can we still talk about how much PG&E sucks?

The title of the thread should be “bear witness to how every thread can devolve into why PG&E sucks and something about heat pumps”