! Oil/steam heat - adding mini splits

grye

Hey everyone.

I have a one pipe steam oil burner. We recently added a large mini split to the first floor (open floor plan), and a mini split in each bedroom.

How do I operate the two systems effectively?

The bedrooms are small, so the mini splits can take care of those easily (and probably more efficiently until the temps really drop).

But the bathrooms and downstairs aren’t covered enough by the mini splits.

I don’t think I can turn off radiators in the rooms I’m just using the mini splits right ?

(New York area - and the mini splits were basically free after rebates, which is why we put them in)

thanks !!

leonz

Speaking as a homeowner and a layperson with a coal stoker boiler:

Turn off the mini splits and use them in the summer.

When was the steam system serviced last? Are the radiators heating up quickly or are the pipes banging? If the header pipe or pipes are sagging/not level condensate can build up in them and reduce the flow of steam to the radiators causing banging in the pipes

If you insist on using the mini splits in winter you can rotate the radiator vents upside down to shut the radiators off OR just shut the power off to the steam boiler and have it serviced in the summer where they can go through the system entirely by cleaning the boiler by flooding the boiler, emptying the mud leg and skimming it if needed. You may need new vents on the radiators and new main vents as well as a new automatic water feeder if the boiler has an original automatic water feeder.

They can improve the boiler and the heating system further by installing a drop header to create dry steam and add two low water cut offs to meet plumbing code, insulating the header pipes and replaciong the bad radiator vents and adding maion vents and insulating the steam mains they are not insulated already.

I hope I did not miss anything :^0

Jamie Hall

When to change from the mini-splits to the steam is one of those questions. Which depends on the particular heat pump system you have and on your electricity rates.

If my recollection serves, your electricity rates are fairly high — so I would expect that at anything much below freezing the steam will be no more expensive to operate than the mini-splits and maybe cheaper — with the added benefit of heating the rooms which don't have mini-splits in them.

Waher

You need a thermostat set up for multistage heating and cooling with outdoor reset. The minisplits cool and heat until an outdoor thermometer tells the thermostat that calling your boiler for heat at the current outdoor temperature would be more efficient than calling for heat from the minisplits; and the thermostat switches over from operating the splits to operating the boiler.

HVACNUT

https://forum.heatinghelp.com/discussion/comment/1821923#Comment_1821923

Pretty invasive with multiple heads and multiple controllers. If they're ducted mini splits, then yes, an interface can be installed and wired 24 volts to any 2 stage thermostat.

Personally I would switch over when I got tired of the draft on my neck and just want to be comfy and toasty.

PolychromeUganda

The mini-splits aren't usually cooperative with a steam system without adding control interface parts. They are built to use their own internal temperature sensors for the indoor and outdoor and refrigerant temperature and adjust the speed of the fan and the compressor accordingly.

Every manufacturer uses its own variations on a generic low data rate serial bus protocol to keep their installed base captive, the walled garden model. Many manufacturers didn't develop a unified protocol and their interfaces are model specific, or design generation specific.

There are two different types of these interfaces;

The first type provides a contact closure interface to call for heat from another heating system. It does that either when the mini-split defrosting, is unable to reach the set point temperature, or when the outdoor temperature is below a specified changeover temperature below which the mini split is uneconomical to operate. Which of those conditions an interface uses is manufacturer dependent. The mini-split assumes that heat is available without advance notice to cover its defrost cycles, which isn't always true for a steam system.

The second type of interface slaves the mini-split to a 24v contact closure thermostat interface. Typically the mini split doesn't devolve to bang-bang maximum output/stop operation instead it maintains its efficiency by inferring a setpoint based on its internal room temperature sensor at contact closure and contact opening and operating as it would if if that setpoint had been set by its remote control.

nb: Mini splits often offer a wall mounted remote thermostat option. This is usually a wired digital remote control that contains an auxiliary room temperature sensor. These usually interface using a digital serial bus, not a traditional 24v contact closure interface. They are usually not helpful for interconnecting a steam boiler with the mini-split.

On the steam system side, there are electrically actuated valves that can be used to open and close the steam line to a particular radiator that would allow an interface to function as intended when the steam heat is already on. Possible and practical aren't the same in this case, the cost per valve keeps them from becoming habit forming. It would be better to use it for the automation of the outdoor temperature change-over from heat pump to steam for the entire building rather than auxiliary heat for the zone.

Finally, I agree with others who have observed that the high electric utility rates in the NY area will make the use of the heat pump function uneconomical at outdoor temperatures below roughly 40°F. The cost comparisons used in government literature tend to either assume it will supplant electric resistance heating or make assumptions about the relative cost of oil and electric power that reflect a municipal government or industrial electric power rate that is between 1/5th and 1/20th the residential rate.

The simplest thing is to stop using the mini splits between mid-October and mid-March (roughly). The mini split outdoor unit can be damaged by ice inside it. It may have a de-icing heater in its base. If you want to stop using the mini-splits in the winter and shut off their power you may want to cover the outdoor unit to prevent ice from accumulating in the base where it can damage the outdoor heat exchanger tubing.

CoachBoilermaker

@grye Did you ever find a good local boiler service tech in Westchester?

CoachBoilermaker

A neighbor told me that he's got heat pump for temps above 10F. Below that, he's got oil/steam as back up. Is that a viable approach?

Kaos

This all comes down to your energy costs.

I'm in the land of expensive oil and reasonable electricity so oil is about 3x the cost of a heat pump. That means you want to run the heat pump as much as possible and only have the boiler kick in when the heat pump can't keep up.

A simple way to get most the most out of your setup is to run the the living room wallmount at a temperature you want and set the boiler to kick in a couple of degrees bellow this setpoint. Since hot air raises, this will also provide a good part of the space heat for upstairs rooms without the noise issues of running those wallmounts. You might want to bump up the boiler setpoint in the mornings to get some extra heat upstairs when you wake up.

ethicalpaul

https://forum.heatinghelp.com/discussion/comment/1822297#Comment_1822297

I think that is highly optimistic. I have my mother's heat pump switching over at 30F

pecmsg

https://forum.heatinghelp.com/discussion/comment/1822297#Comment_1822297

that deepen

Your comfort

Cost of fuel

grye

https://forum.heatinghelp.com/discussion/comment/1822054#Comment_1822054

I had thought that turning off certain radiators messed with the pressure the system was designed to operate at.

Ideally, I would turn off the upstairs bedroom radiators and operate the bedrooms just on the mini-splits (since they don't have to be on all day when nobody is home). Then I would leave open a few downstairs and the bathrooms.

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1822542#Comment_1822542

It won't mess with the pressure. What it will do is force the boiler to short cycle, since it will now be wildly oversized for the load it is powering. This is not particularly good for efficiency…

Also, remember that just closing the valve on a one pipe steam radiator is not good practice. That valve is there so you can maintain the radiator while the system is in operation. A better ploy with much the same effect, if you really want those radiators off, is to turn the vent upside down. With more effort, you can also put a small valve between the radiator and the vent and close that.