Alternative controls for hydronic heating system

andyatchison

Hi All,

Control question here: I have a geothermal heat pump connected to an in-floor hydronic heating system in our home, with concrete floors throughout. For a couple of reasons, I'd like to eschew a traditional thermostat set-up in favor of programming the system based simply on the duration and frequency of run times. 

I'm currently using a regular thermostat, but limited to 4 set points daily. I'd ideally like the system to run in a series of adjustable on/off cycles, say, on for 2 hours, off for an hour.

I know the answer is to invest in a plc/control system and fully program it, but wondering if anyone had a more clever (read cheaper/simpler) idea. 

Thanks very much!

EdTheHeaterMan

When you say Adjustable on/off cycles... what is the purpose of adjusting them?
If you say "because the outdoor temperature change will require longer or shorter ON cycles" Then I might suggest constant circulator operation with outdoor reset control of the water temperature from the heat source. There are several control systems that already do that.
Store the unused heat the heat pump uses in a large buffer tank and maintain that temperature by a tank thermostat as needed. Control the floor temperature with a 3 way or 4 way valve connected to outdoor reset control to maintain the floor temperature as required.

pecmsg

The floor temperature should be controlled by sensors in the floor with an outdoor reset.

The Geo heats a buffer tank, size to be determined.

andyatchison

Thanks for the quick reply, Edward. The house has a couple of unique features - it's ICF, with concrete first floor, second floor, and roof - a tremendous amount of concrete, therefore mass.  It's like a locomotive, and changes temp very, very slowly.  We also have a wood-burning masonry heater, which produces roughly 300,000 btu per firing. We have varied schedules, and sometimes host large gatherings in a 3,000 square foot house. 

I am not familiar with "outdoor rest control," but feel that I could better control the house manually, given what I know about our family schedule and long term weather forcast - versus any sort of sensor reading current temperature. 

I also want to prevent our loops from running for extended periods of time. And, of course, I kind of like controlling things!

Jamie Hall

Your system -- which includes very high mass -- is, as you note, singularly unresponsive to efforts to change something. Including your efforts to control it. It will work best, and you will be most comfortable, if the system is controlled -- by a floor thermostat and outdoor reset of the circulating water temperature -- to maintain as close to a constant temperature as possible. This will occur with constant circulation of temperature controlled water in the floor, from that buffer tank and with the outdoor reset controlled mixing valves as noted.

Now. If you want to change the temperature in a space for short periods of time, you can't do it with the floors. You can do it with your monster stove, or you could consider adding panel radiators to your system for local space heating.

EdTheHeaterMan

I am not familiar with "outdoor rest control,"

You should become familiar with this concept. The basic idea is that any structure, be it paper thin sheathing on a wooden frame, or a massive block of concrete, will loose heat based on the temperature difference from one side to the other side (inside to outside).
When the outside temperature drops, the inside needs more BTUh added to the inside to stay the same temperature. Likewise when the outside temperature increases the amount of heat added needs to be less.

Outdoor reset has an outdoor temperature sensor and an indoor temperature sensor.
A sort of average of the two temperatures lets the heat source know if higher or lower water temperature will be the correct amount of heat to maintain the desired indoor temperature. Pumps can operate at lower speeds (use less electricity that on/off operation) to maintain a constant flow of the correct water temperature in the radiant heat system.

Do the research and find the one combination that has the most display screens, so you can monitor each different function and tweak it daily (since you like to be in control). The more screens and display LEDs and lights the better!

Just some random thoughts

By the way, what happens if you need to be away from your building of concrete for a week or so? Who is in control then? Wifi and Bluetooth boiler control connections to you smart phone can allow you to say in control where ever there is an internet connection available. Even if the boiler is a heat pump. Now that is real control if you ask me!

Dave Carpentier

One boiler i was looking at can use ODR data from the local weather stations on the internet.
Presumably they use local "current" temperature, but I wonder if some can use forecast temperatures for a lagging system.

EdTheHeaterMan

Dave Carpentier said:

One boiler i was looking at can use ODR data from the local weather stations on the internet.
Presumably they use local "current" temperature, but I wonder if some can use forecast temperatures for a lagging system.

Now you are getting too far into the "what if department". And think about it... do you really want your heating system to be dependent on the accuracy of a weather forecaster? Yesterday, my weather girl said it was going to rain today... It didn't!

hot_rod

With a geo heat pump you are probably running in the 110- 120 F range?  So probably not a lot of room for outdoor reset control?
Thr large wood stove probably holds the radiant thermostats off, so more mass to catch up when the fire is out

andyatchison

Thanks, guys. Good stuff here. Supply water to my floors goes in about 80 (comes back about 70).  I do have a buffer tank, 20-gallon. The ODR makes sense, and I'm going to look into it further. Correct that nobody, including me, is able to make quick temp changes to this house... roughly 100 yds of concrete. 

One point I didn't explain very well is the concern of my geothermal heat pump (3 Ton Water Furnace Synergy 3D) running for an extended period of time... if it runs for 12-16 hours or so solid, my well temps drop and the heatpump stops with a low temp warning. I have 4 wells at 150' deep, and we just barely dip into the water table, but our soil conductivity is quite low - now, much too late, thinking I should have added a 5th.  I haven't measured incoming water temps, but can feel the fittings are quite cold, and thinking this is poor efficiency down in these temps. 

Anyway, the control I'm after is primarily to address this issue - to limit how long the system runs continuously. I seem to have no problems if if the wells can rest briefly. But worried that any automated system comes with a risk of prolonged run times.

hot_rod

Will 3 ton cover the heat load? Seems with 80-90 SWT, the heat pump should be running efficiently even at low source temperatures?
Collect  some temperature data, maybe have a heat pump tech check the unit for proper operation.

It n my at be useful to have a dual fuel system, switch to Lp when the hp falls behind. That could be a simple temperature controller, watching the loop temperature with a programmed time out period. A basic Ranco or Johnson Control digital setpoint has functions like that 

andyatchison

Hey Hot Rod. I would like to measure the well temps for air. 3 tons seems like it should be more than sufficient for our application. 

The LP route feels like a lot of expense and hassle compared to the solution I feel should be out there, somewhere... a thermostat that let's me program small breaks in the run time. 

My best idea so far is to wire up two programmable thermostats, so that I could program in 4 complete daily cycles... but was hoping that someone manufactured a more elegant version of this. 

hot_rod

But if the wells cannot keep up, what happens on design days? Or days below design?
AS the wells cool don’t you also start loosing output, you no longer have the 36,000 btu output?

ethicalpaul

I use a “smart outlet” hooked to my Apple Home system (I’m sure Android and Alexa offer the same)

it lets me set up as many on/off settings as I want. 

You can make it drive a relay in parallel with your radiant thermostat to force it to run when you want it to in addition to when the thermostat calls.

Jamie Hall

That your well water temps keep dropping tells me one thing: you simply don't have enough source capacity to handle the load. Basic thermodynamics. A heat pump operates by extracting a certain amount of heat -- X btuh -- from the source, in your case groundwater, and releases is, at a higher temperature, in your house or whatever. There are only two places that X btuh can come from: reducing the temperature of the source, or bringing in more source water at the initial temperature from somewhere else. No other options. In order to have stable source temperatures, there must be water coming in to the system from somewhere. Otherwise, you have to live with dropping water temperatures, and hope that there is enough mass of water present to provide the total heat storage you need.

Now you need a certain amount of power -- btuh -- to maintain your house temperature. Can't get around that, either. Breaking up the run time of a heat pump (or anything else) simply reduces the power it can deliver. If that accomplishes the objective of keeping the source temperature a little higher, that only tells you that the power available from the source is inadequate to power the hourse.

Sorry.