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Bernd  Fighting algorithmic racism like John Henry  2yr ago (image post)   Edited 1yr ago   4982 thread views

Mini Split Heat Pumps: Not Significantly More Than You Reasonably Need To Know

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If your main heat source is hot water baseboard, heated by oil or gas, there is another down side to heat pumps. New England had a very harsh cold snap a few weeks ago and I went on a call where a customer had their heat lines freeze and split because they were heating the room with the heat pump and the hot water baseboard lines were not running because the air temperature in the room with satisfied with the mini split. Unfortunately the hot water lines to the baseboards in the outside wall got so cold in one room from not running that I had to isolate that zone. When I went there during the cold snap, they were completely frozen solid. I isolated that one zone and will have to go back and repair several splits. I have seen a similar thing happen before when someone was heating the area with a wood stove, the air was warm but the outer edges of the house where piping was got too cold.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
That's really useful info, and something I was totally unaware of living in an area without gas boilers or really cold weather, thank you!


Of course whoever installed a water system would assume the heat would be on in cold weather. Were the pipes outside the insulation layer or something? That's really strange--seems like it would be very lossy in normal use.


I have some piping running through my crawlspace under the insulation, and should really improve it on principle despite it never getting cold enough down there to freeze them.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
					

				
			
		

	







	

	

		
			

			

				

			

		

			


				

					
Great writeup! I would appreciate a lot more posts on this forum of this nature instead of the latest celebrity racism gossip nitpicking.


Also... does anyone know a similarly good writeup for people being kept hostage by the EU green commissars?


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	







	

	

		
			

			

				

			

		

			


				

					
In summer, I get annoyed at my retired parents for setting their small house two-room mini-split to 72F. They refuse to believe that’s the temperature of the air coming out of the things, not a thermostat temperature the device will smartly adjust toward.


Set it to 60, please, to mix with the 90F New Mexico air and approach non-sweat temps, please. You’re ALREADY energizing the coil, you’re already spending money, just turn it down twelve degrees!


And turn off the two standalone fans, just let convection move the cold air into all four rooms. You’re using up all the electricity you’re “saving” from 72F air instead of 60F.


Seriously. I lived there for five years, I know how to cheaply heat and cool that house.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
It should be the room air temperature, because the indoor unit reads the intake air temperature and tries to get it down to the target temp (or uses the remote's thermometer, if you have a "follow me" setting). That's odd and maybe a sign of something wrong.


Some of these things do have weird behaviors, which I'll post a bit more about at some point. Mine goes to the lowest output once it gets 1 degree from the set point, rather than waiting to exceed the set point before throttling back. So if I want a 67F room it should be set for 68F.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
This model gives no way to read current room temperature. The remotes are dumb infrared output-only devices, sending the entire desired settings on each button press. both remotes are identical, and work for both units, independently. I have a hard time believing it is intended to do anything other than have a desired output temperature, since I’ve seen absolutely no indication of any thermostat-style behavior.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
What's the model? If you look in the top you should be able to see the temperature probe in the inlet path, under the filters


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	







	

	

		
			

			

				

			

		

			


				

					


If you live in the UK or Germany, uh… I’m sorry. If I was living there and couldn’t afford a plane ticket out, I’d get some of those charcoal burners and maybe tape for the windows.




Plane to where? Also, Germany seems unlikely to get to "charcoal burners" stage.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
Well, the majority of their "green" energy right now is coming from burning wood chips, so in some ways they've already regressed past charcoal lol


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
					

				
			
		

	







	

	

		
			

			

				

			

		

			


				

					
Just did a job with a guy who was a wealth of information about these, having installed 10 of all different makes over 15yrs. He confirmed my suspicions about Mr Cool DIYs: it was the only one he'd had leak, because of insufficient sealing on the factory-filled line set.


His son also switched from propane to a heat pump, and it sounds like his before and after fuel costs were right on my graph: about 1/3-1/4.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	







	

	

		
			

			

				

			

		

			


				

					
I was about to comment on ground source heat pumps, but you beat me to it.


You can do some DUMB shit with those; including just dropping a couple hundred feet of tubing down a well shaft.


I find the main advantage of them is they are decently efficient DIYable single room COOLING AND HEATING, which is sick.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
I have a blind spot on vertical ones because they're definitely not an option here; my well wouldn't qualify as "marginally acceptable" as a water source in most places, and you'd have to be impossibly lucky to get a shaft with enough water layer and flow to work as a ground source. In a place like florida they'd be amazing, but in florida you could just warm your pool instead.


Geothermal in general has that "as much art as science" problem. There's research asking "wait, how much heat could pump from the ground below a city without causing problems?", and there's not much in the way of hard numbers yet, especially in the cold climates where a ground source is important.


That's one reason I think co-gen will be a big deal. Having a huge volume of power plant condensate to work with takes out the guesswork, and there's no technological advances needed over current high-temp cogen systems.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
In yet another victory for thermodynamics; it turns out that a large thermal mass is just fucking better for the shit we want to do if you can max out capacity.


It's like that old tmblr post; that no matter what you  are doing the most efficient form will always be whatever the train equivalent for the field is.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					


that no matter what you are doing the most efficient form will always be whatever the train equivalent for the field is




is it entire interesting part? Or have they got interesting examples?


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
A conceptual train.


Imagine you are, for example, lifting mass into orbit, or moving people between floors in a building, or cooking food, or digging a big hole.


What is the most efficient way to do all those things?  Orbital elevator theoretically/BIG ROCKET currently, Escalator, BIG pressure cooker, BIG bucket wheel excavator.


The more the spirt of the thing is akin to a train, the more efficient the thing is, and also the more RIGHTOUS the thing is because trains are fucking sick


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	







	

	

		
			

			

				

			

		

			


				

					
I'm curious what your house looks like that one head in the living room heats the whole place reasonably evenly. One of the best advantages of mini split systems is generally that it's easy to achieve balance by placing multiple heads or units in a building, so you don't overheat one area just to get heat to another, or you can leave marginal areas of the house less heated than occupied ones. Though that might just be a reflection of my town being relatively rural, with large weird houses being the norm.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
Maybe "house" oversells my trad hovelcube a little. It's much smaller than the American average, but then so are many castles. There are a lot of "reasonably sized houses" in the pacific northwest for some reason, and it's of typical construction for there.


If you have a ton of doors you can't leave open, adding a second unit or a multi-split might be the best option, but the airflow is high enough to push heat up the stairs and keep my 2nd floor within a degree of the 1st.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
Hey, when we're talking heating, my buddy just bought a 3,000sqft home with a weird multi split level first floor. He's spending $600/month on oil heat already and it's only November. My ranch with a heat pump and a woodstove has me feeling bad even talking to him. Small house small costs. I don't even want to think about what my parents pay in heat.


Better a small home you can keep nice than a big house than goes to shit. I see that too often around me.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	







	

	

		
			

			

				

			

		

			


				

					
Great post, I didn’t learn much new stuff,  but it was a very enjoyable read. You have a very good point about high potential for grid instability on very cold days. I have a natural gas cooking range that can do something like 30-40k BTU combined, should be good enough for emergency situations, assuming regular air changes  to avoid annoying high CO2 build up.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
I hadn't even thought about using a cooking range for heating, that's clever. Wouldn't even be too inefficient if you had heat recovery ventilation.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
					

				
			
		

	






	
		

			

			

				

			


			
			
			

				

				
					

						
							
							
								



	

	

		
			

			

				

			

		

			


				

					
Depending on where you are and how high your water table is; you may be able to get a vertical shaft drilled for fairly cheap (except in the places where they take 2/3 of your liver, your kidneys, and your first born on the way out.)


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



							
								



	

	

		
			

			

				

			

		

			


				

					
Our condominium just installed geothermal recently, just finished in the autumn. Came at a very good time, one might say.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
Let me know how it goes! Any chance you could snap a few pictures? I have zero local sources on ground source installs.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
					

				
			
		

	



							
								



	

	

		
			

			

				

			

		

			


				

					
It does! I'm in a similar situation with shade trees, but seriously thought about lopping them all down and doing it anyways. It was tempting to put a big "geothermal!" mark at COP5+ on the graph, but it was already too crowded.


Had to cut almost everything about ground-source stuff for length, but I think it's the future in cold climates, and Europe is making a serious mistake trying to push air-source units rather than street-level ground source. There's a tremendous amount of wasted heat flowing down every sewer pipe without even having to do any digging, and ultra-low-temperature local cogeneration would make even a simple gas turbine about 260% efficient.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					


There's a tremendous amount of wasted heat flowing down every sewer pipe without even having to do any digging




I've thought about this before, and what I came up with was water-water heat exchangers in shower drains, between the outflow and the cold inflow.  You'd want a thermostat-controlled valve to keep the shower temperature from drifting, but that'd be an improvement to UX even without the HX. Dishwashers could do the same thing to recycle heat from prewash->wash->rinse. (IDK if warm rinse would be more effective, but it'd use less energy to dry.)


Putting the recovery device as close as possible to the producer of warm graywater gets you the highest-grade heat, and also means your HX doesn't have to tolerate actual poo. In the individual house/apartment, drain heat is intermittent and unreliable, but conveniently correlated with the need for hot water.  Building-level heat capture could smooth out the availability with a big buffer tank, but hot sewer water is diluted with cold.


In large apartment buildings, the owner could install a cold water pre-heater (to say, 20°C or so), using the most economical type of heat for the climate, which would reduce cooking energy (and time) in winter.  People might naturally use less hot water for washing hands too.  A couple of years ago, I measured the flow rate and hot-cold temperature delta of my kitchen faucet in winter, and now whenever I run the hot water waiting for it to warm up, running through the back of my mind is, "YIKES 13 kW!"


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
							



	

	

		
			

			

				

			

		

			


				

					
I'd like to read your write up of the geothermal material that you had to leave out. Any chance of a supplementary post?


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
Next post is focused on all the culture war you could see oozing from the seams in this post lol.


After that I was thinking about a electrical generation post. Unfortunately I don't have any firsthand experience with ground-source heat pumps, and there's so much propaganda around all things heat-pump that I wouldn't want to post my research as trufacts without independent confirmation. Maybe Stefferi could help with that.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	



							
						
					

					
				
			

		

	







	

	

		
			

			

				

			

		

			


				

					


The formula is Carnot COP=Thot/Thot-Tcold




Your meaning is clear, but some parentheses would not go amiss: COP=Thot/(Thot-Tcold).


Also, holy shit this is a fun post, at least for those of us who have a proper appreciation for autistic infodumping. Thank you for writing it!


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
I guess this is a good time for me to complain that division should be the last order of operation, because (1) ime that's usually what you want to minimize parentheses and (2) that's the way it works when you're writing equations in latex or by hand and drawing horizontal lines with a numerator and denominator.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
							



	

	

		
			

			

				

			

		

			


				

					
I didn't find the meaning very clear, I don't get how sluts divided by sluts minus cold sluts makes any sense. But I also concede I don't have much experience using thots as a unit of measurement outside of STD questionnaires.


Still a fun a post for the parts I did understand, lol at Europe for having expensive energy costs, they did a good job of screwing themselves over on that.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
							



	

	

		
			

			

				

			

		

			


				

					
I hope people find it useful! And thanks: that's the greatest/only compliment(?) my writing has ever gotten.


Haha, yeah, just adding clarity... I definitely didn't forget my default order of operations rules from kindergarten or anything... <_< >_>


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
You can also write the variables as Thot (from T<sub>hot<\sub>), but then I wouldn't get to laugh at "Thot policing".


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
Testing if we're using the new math markdown module


$$ COP = {Thot \over Thot-Tcold} $$


Apparently not, damn.


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
@ZorbaTHut is it possible to get a markdown math module on here? It'd be very convenient for doing formulas by text instead of having to link images. I don't know anything about modern website stuff, but it looks like some people use stuff like this https://www.mathjax.org/ tutorial thingy: https://jupyterbook.org/en/stable/content/math.html


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
I think this mostly comes down to developer time. We need to do a revamp of the markdown setup anyway, but once that's done, this is certainly possible . . . if someone wants to put the time into it. I don't think it's likely to be a high priority for a while.


So basically, talk a friendly coder into doing the work and I'll happily put it in, but I'm not going to promote it for quite a while :)


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
							



	

	

		
			

			

				

			

		

			


				

					
Yeah, I felt dumb for asking for it when we don't have single-line-spacing yet, my bad


				

				

						

							

								
							

						


						
					

				
			


			

	


			
			 
				
					

						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	



						
					

				
			
		

	




	

	

	

	

	

	
	

	
	

	
 















	






			
			

		

		
			
				


	

		
	


	


		
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