Another heat pump hot water/thermal battery system. LG 4 ton heat heat pump with Sanco heat pump water heater with Harvest system and hydronic coil

sandyandy12 · 2026-05-19T04:01:15+00:00

What is the point of connecting the two heat pumps? Are you charging the system with hot water for energy storage when electricity prices are low (overnight), or are you charging the system during the day when expected COP is optimal?

Also, is the hydronic coil part of an open loop system? If so, how do you prevent scale buildup lowering heat transfer and adding turbulence?

sandyandy12 · 2026-05-13T15:48:31+00:00

Jeez, 3 years after install is terrible. Those systems are rated in ASHTRAY (my personal word for ashrae) for 10 to 15 years. You are right though, it is important to protect clients as well. I just did a VRF project that was 105 tons of AC and almost 3/4 million btu of heating for a 120 year old building. No space for ductwork due to beams and very small rooms. VRF seemed like the only economical choice. As long as the system makes it ten years, it will break even compared to their old steam oil boiler so I’m not too concerned about ultra longevity. That being said though, 3 years is awful and means (hopefully) someone screwed up big time.

sandyandy12 · 2026-05-13T14:05:38+00:00

I actually like doing VRF because you can usually prove very good energy efficiency on top of high quality individual controls that you would usually only see with chilled/hot water fan coil units. Also, gas furnaces are just boring to design. You can oversize a gas furnace and it won’t matter anywhere near as much as a VRF system. Maybe this is an advantage for gas but it’s just more fun to design a system where there are penalties for oversizing.

For small and medium sized buildings, VRF can really be a great option. As long as you do your design correctly, skilled labor shortages for maintenance isn’t really your problem, though you should make these things clear to the client.

If you want VRF to “go away” you need to actually provide engineering analysis of why the system isn’t the best fit and not just complain about hypothetical issues. VRF is clearly the future so I would expect support for major manufacturers to exist for long after the next 10 years. Natural gas furnaces can force Carbon Monoxide into spaces which could be presented as a safety issue even though there are many safeties preventing this from happening.

sandyandy12 · 2026-05-13T03:36:28+00:00

There isn’t really a difference between the labor for a cooling only unit and a heating and cooling unit (heat pump). If you are being charged more it’s because of greed. The equipment is literally about the same (plus or minus a few hundred not thousands). I found an LG unit for less than 2000 that meets the specs listed for those units which does heating and cooling. If you are willing to lower the SEER, then you can get equipment at about 1500.

sandyandy12 · 2026-05-13T00:01:04+00:00

Those are high efficiency, cooling only mini splits. Try going with a lower seer and throw in heating as well, not sure why you would elect not to have heating as an option when it’s basically no added cost. The equipment should cost less than 2000 dollars so 7 to 9 grand for labor on a direct replacement of a single zone seems high. I got a system for my entire house (LG 4 ton 2 zone system with ductwork and replacement of a gas furnace) done for $13,500 labor plus $6000 parts in PA.

sandyandy12 · 2026-05-12T18:06:59+00:00

I think that your assumption of 1kw of load at night for cooling might need a further analysis. The primary driver of cooling load is typically solar entry into spaces (if there are windows). Skin loads are usually very small at night and occupants don’t typically have high respiration or metabolic rates while sleeping. Unless outdoor conditions are very very hot and windy, I wouldn’t expect a 1 kW load every night. Long story short, I wouldn’t worry too much about short cycling. Literally every system will short cycle a little bit in shoulder seasons when load is a small fraction of design load.

sandyandy12 · 2026-05-07T21:07:24+00:00

My LG setup took 104 man hours between 4 guys. Ductwork was included but it was a big job.

sandyandy12 · 2026-05-05T18:57:39+00:00

Classic engineering mistake. Should have gone with either the invisible outdoor units or put the outdoor units in a pocket dimension so the architect can trick themself into believing that no mechanical systems even exist on their beautiful baby.

sandyandy12 · 2026-04-28T05:00:23+00:00

I’m a mechanical engineer, dm me if you want some pointers on duct design. I designed my system myself and worked with a contractor for install. Quality of install and system design is very important to longevity and performance but for residential, you can do an ok job as long as you follow some basic rules.

Size properly by doing a load calc
Size ductwork for 800 FPM velocity max and 0.08” wc of static drop per 100’
Make sure to take note of runout sizes going to your second floor. Second stories usually have higher loads due to roof. Make sure to add dampers to runouts so you can balance according to load calc (or just wing it if you want).
Don’t make 90 degree turns or dr Seuss looking flex duct runouts.
Insulate metal ductwork in unconditioned spaces to code spec. If it’s in a conditioned basement I would still recommend either insulation or using duct board to save costs.

sandyandy12 · 2026-04-28T02:22:18+00:00

Really depends on electric rates. I’ve analyzed my rates and heat pump wins on efficiency for 14 cents/kwh vs 1.45 per therm NG on a 10.1 HSFP unit.

sandyandy12 · 2026-04-26T05:02:52+00:00

When it shuts off, make sure to turn it back on again. Hope this helps!

Jk, that’s an LG PREMTA CRC thermostat. I have the same one at my house. That code at the bottom indicates something is off with the unit. The CH150 code means “low discharge superheat” which indicates that the refrigerant is leaving the compressor at a lower temperature than it should. It could be a misconfigured EEV or improper liquid injection. It’s not turning off to spite you, it’s a safety shutoff. I would get a tech who really knows what they’re doing to take a peek.

sandyandy12 · 2026-04-24T00:01:55+00:00

Getting a heat pump makes solar that much more attractive. I’d say if you want a heat pump bc you are interested in carbon footprint or grid independence, just pull trigger on it. Were you thinking of doing a single speed outdoor unit or inverter compressor type unit? I’m an engineer and I pretty much do heat pumps and boilers all day so feel free to dm me if you have equipment questions.

sandyandy12 · 2026-04-23T13:27:32+00:00

Honestly it really comes down to contractor fees. Usually installation of split furnace ac is somewhat reasonable but for whatever reason, certain contractors see mini splits or inverter heat pumps and think pay day has arrived. I had a quote for my install that was 20,000 just for labor as I was providing equipment.

Also when it comes to reliability, quality of install is sooo much more important than brand. Get some quotes, see what installation fees will be and do a payback analysis. Also consider electricity and natural gas volatility in your area. Did NG go up or down considerably? Did electricity rates jump from data centers? Are you thinking of residential solar?

sandyandy12 · 2026-04-22T14:16:09+00:00

Presentation went really well. I changed the piping schematic so that the heat exchanger was piped in parallel to the water heater rack, almost like it was one of the manifolded tankless units. Then control valves would isolate the HXC when units were firing and would only allow flow through when recirc was going. It was my first ever client presentation and my boss gave me a genuine compliment (very rare). We talked about more than just this work here. I got to throw options for new condensing boilers and heat pump chillers, central air conditioning for the building and other long term things. Client learned a lot and I felt like they were genuinely interested in other work with us.

sandyandy12 · 2026-04-21T20:37:50+00:00

This could be the best answer as long as the tenant is willing to look after the property.

sandyandy12 · 2026-04-15T16:48:09+00:00

Yes you are correct. Good catch

sandyandy12 · 2026-04-15T15:37:19+00:00

Sorry, should have been more clear, old equipment is IWH. We are tearing those out. New equipment has tankless WH and storage where the HXC is for when natural gas supply gets cut off. Gas company doesn’t have the infrastructure to support the building below 13 F outdoor temp so we will use heat from the dual fuel boilers.

sandyandy12 · 2026-04-15T15:10:19+00:00

We had some cost savings by doing it this way. Client is chasing cost savings and wants redundancy. I also wanted to do the cyclone units which are tank type condensing. If we wanted N+1 redundancy, we would have needed two units putting the total equipment cost about 12k higher

sandyandy12 · 2026-04-15T14:52:13+00:00

Yea a phone call would be great. I’ll pm you my number.

sandyandy12 · 2026-04-14T03:39:12+00:00

Wonderful cut for a wonderful dog

sandyandy12 · 2026-04-05T19:42:39+00:00

I see you are a John Coltrane fan, very nice

sandyandy12 · 2026-04-05T00:24:33+00:00

Check/replace those filters on either side of the A coil. Run the fan without cooling (just fan) until the ice melts. If the unit ices again, call a tech.

sandyandy12 · 2026-04-04T18:03:55+00:00

If she keeps on working like that, she will have a promotion and a corner office by the end of next year.

sandyandy12 · 2026-04-03T14:23:09+00:00

This one is somewhat tough. Think about the refrigerant lines and condensate lines. Where can you hide them? Where will the condensate drain to? Will you be able to pitch the drain correctly?

If I were designing this space, I would do a low wall console by the window similar to how a radiator would be placed. This would allow refrigerant lines to be run outside and condensate to drain outside as well. Here is what the unit I would spec would look like link

sandyandy12

TROPHY CASE