Chiltrix Monoblock systems
I’m about to purchase a Chiiltirx CX35, for an infloor heat system. I’m comfortable with the heat load/unit size. My questions are:
1- as a DIY, are these monoblocks as plug and play as the sales says. Meaning, does the unit simply regulate it itself, without us installing controls inside the house, simply by monitoring return temps and flows and ambient external temps? Do we just hook up the unit power and go?
2-COP ratings are hard to suss out, as the actual COP will depend on factors more complicated than the simple tables state. Sales says that in Massachusetts heating degree days, we are looking at a cop of 4ish, whereas the simple charts look like 2-ish. Does anyone have some consumption data that might bear that out their claims?
3-How is the repair scene, or is it too new for this to be known yet.
The system looks just right for our in-floor heating, which run the floor at 110. Just looking for independent confirmation of the sales claims.
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I've been running the predecessor, the CX34, for three years.
It really is plug and play, you hook it up, turn it on and program in the temperature. However, you have to have some sort of thermostatic control on your emitters, in this case your floor. That can be as simple as a zone valve and a thermostat. I highly recommend using the outdoor reset which is built into the Chiltrix.
COP for heat pumps is a tricky business, it depends upon the heat pump, the climate and the building. This spreadsheet gives an indication of the calculations you have to do:
https://docs.google.com/spreadsheets/d/1uxIOKJJKmOCMtxbWPZXU2WQRnSwHColipUuQ5uPa_9M/edit?usp=sharing
The big thing to look out for is the heat pump output falls off the table at low temperatures. If the heat pump can't keep up you have to use some sort of backup heat, I use resistance electric which has a COP of 1.0 which lowers your overall COP.
This is a sheet I did for Boston for a different heat pump, the Arctic. It has vapor injection which does a better job of retaining capacity at low temperatures:
https://docs.google.com/spreadsheets/d/1KmnOjq_MEQ2fNqj5AZvLSXHkNx3dwDPvn_SNBV2iHMA/edit?usp=sharing
I can help you make a table like that for your setup.
Have you done a Manual J or other heat loss calculation?
Thanks for the reply.
I am using historic therm usage, which I've broken down to coldest day BTU/hr historically. Current "boiler" is a Polaris gas condensing hot water heater...35 years of data. Aging Polaris will be on its own manually switched loop if Chiltrix goes down, or can't keep on on a freak -20 evening. The two heating loops, Chiltric and Polaris will always be manually switched if necessary, and isolated from each other.
The in-floor loops are an existing system, so floor temp sensing thermostats currently control the loops. There will be a Taco plate heat exchanger, so the existing in-floor system remains exactly as it has been functioning with its own pumps for years.
The loop from the monoblock to the heat exchanger will have glycol. Heat exchanger heats water in chilrix's buffer tank. Buffer tank supplies heat to in-floor loops.
How is your unit doing? Any problems? Are you in the Boston area?
I'm in Washington, DC.
Heat pumps don't generally work well with heat exchangers. Efficiency is all about temperature delta, you want to keep it as small as possible. In order for a heat exchanger to work there needs to be a temperature drop. You want water coming straight off the heat pump going out to your loops without any mixing to the greatest extent possible, then adjust the setting of the heat pump to give the needed water temperature.
The biggest mistake you can make with a heat pump is to think it's just like a boiler only noisier. With a boiler, a BTU is a BTU, mixing is no problem. Setups that work well with boilers often don't work well with heat pumps.
DC does have a point, but you can still make a plate HX work. The important part here is you don't want any mixing valves on the space heat side. You also don't want to over-pump the floor heat side. Ideally the flow rate on both sides of the HX should match, if not possible, the flow rate on the monoblock side should be higher.
How many gallons is your existing heating loop, the oversized plate HX to get the low approach temp you want might be more than the cost of the extra glycol.
You can also run plain water out to the monoblock, this is what I'm doing in zone 5.
To get the same temperature change on both sides of the heat exchanger you have to have the same flow rate on both sides. If you don't have the same temperature change it's going to be very difficult for the water coming out to be as hot as the water coming in.
Problem is, the heat pump is going to be modulating and adjusting the water flow, and there's no way for the circulator on the other side to know what that flow is.
I'm also not crazy about the heat exchanger feeding a buffer tank, that sounds like a recipe for mixing. It also doesn't provide any short-cycle protection to the heat pump. If anything I'd put the buffer tank on the heat pump side and plumb the heat exchanger like a regular load. Then you can synchronize the circulators on either side of the heat exchanger.
I still think you're better off just skipping the heat exchanger and doing glycol throughout. I'm not as courageous as you are in terms of running plain water.
What did you end up doing as far as freeze protection valves? I am getting ready to set up my monoblock shortly and considering the same.
What is your calculated heating load and design temperature?
I haven't done a calculated load, because attributes of the building envelope are all custom and thus not included in theoretical models. The non-standard attributes get entered as penalties in theoretical models. When models were attempted in the past they vastly disagreed with the historic therm use. In fact, I had to hang up on the Arctic sales guy when he ran the numbers and said I needed a high temp system, despite 35 years of metered evidence.
By the way, the system uses rot gut simple non-modulating controls...on at 110f when thermostat call for it and off when thermostat reaches temp.
OK, but you've got historic therm usage.
The weather station at Logan Airport has a 99th percentile temperature of 13F and an average annual minimum of -6F, you want to size somewhere in between them.
At a water temp of 113F the CX35 has a capacity of 22K BTU/hr at 14F, 18.6K BTU/hr at 5F and no rating below that.
Even though they advertise it as "3.5 Tons of heating," that rating is meaningless. For your application you have to assume 18.6K at 5F and 100% backup heat below that. That's where you might run into trouble with satisfaction.
Historic BTU/hr worst heating month of the year is 15,500btu/hr. I am waiting for this years data to maybe override the long term historic BTU since it is so cold. I have since removed the domestic HW from this load (rheem heat pump h20 heater). My calcs show a 20% reduction in BTU load for the domestic hot h20. However I am leaving the hot water btu's in the 15,500 number for safety sake.
It's not completely clear, but from the way you're putting it I think you're just taking BTU's for the month and dividing by hours in the month to get BTU/hr. If so, you need to project that out at least as far as your 99% temperatures. This article tells how:
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
According to Wikipedia the coldest month in Boston is January, with a mean temperature of 29.9F. Just back-of-the-envelope, if you're average 12K BTU/hr at 29.9F, or 40F below room temperature, at 13F, your 99th percentile temperature, you'd be 57F below room temperature and would expect a load of 57/40*12= 17K BTU/hr. At your mean average low of -6F you'd expect a load of 76/40*12= 22.8K Btu/hr. Somewhere around 6-7F the heat pump is going to run out of capacity and you'll have to use backup heat.
The heat exchanger suggestion was from John at Chilltrix. He increased the buffer tank size with that exchanger addition. The exchanger he spec'd has a 2 deg delta, so the 113 from the Monoblock feeds the system loops with the 110f we've used and been happy with, as a non-modulating temp for years. Glycol in the loops would mess with the loops, and pumps, which took me a couple years to get right when I put this system together years ago. I would have to change pumps to the system, and simply don't want glycol running all over the house. There is the problem of the stinky hard to clean mess when leaks (mice) occur, and the shear problem of draining the sytem and what to do with gallons of glycol. For me, glycol in the system would be a deal killer.
Zone 5 is colder than Boston area. we are 6 I think at this point I think. HOw do insure you don't freeze in the monoblock?
" Glycol in the loops would mess with the loops, and pumps, which took me a couple years to get right when I put this system together years ago. "
Could you explain this statement further? I've run glycol in many systems and I'm wondering what you're concerned with.
the system uses a defunct counterflow EDPM double tube made in the 80's by Bio Energy Systems. The tubing has 2/ 1/4" ID EDPM tubes in 120ft loops, off 1" headers. Runs at 20lbs. Each zone has a Taco 006, quite small bronze circulator 3 or 4 120ft loops. The static pressure must be quite high, though it works quite well as set up now. I am afraid that by adding glycol the static pressure would be elevated beyond where it could adequately force the goop through the small diameter tubes. When I first installed it zones would flow backwards, and didn't start behaving until I installed zone valves on each circuit. Flow checks and drop checks were useless or worked for a few months then stopped working.
Plumbers have always said that there would be too much air in the system, and it would be impossible to bleed. However 35 later it runs well , after the zone valves were installed, and bleeds itself well. So they were wrong about everything in this system, and it didn't work until I did my own seat of the pants redesign and installs. But...I don't want to mess with something that works well.
I would like to know what the gpm rate is. I may just open the bleed valves with circulators on some day, on all three loops and collect the water for a minute and get an idea what the actual gpm is. I don't think its all that much., but I could be wrong.
Since you have zone valves, you really only need one circulator pump. The next time you have a circulator fail, you might consider getting an ECM pump that can run in pressure differential mode, which means it will dynamically adjust pump speed (and thus power usage) based on the number of active zones.
You can determine the static head loss for your zones by measuring the power consumption of your existing pumps and comparing to the manufacturer’s performance data. Or, if you know the run lengths, it can be directly calculated based on pipe ID and the flow rate required to meet the BTU load. With that you can size the circulator.
Although all of my tubing is 1/2” so the pump may be pumping against less static head than you have, the radiant system covering 3400 sqft is distributed by a single Grundfos Alpha2 delivering a max of 8GPM at ~60w (much less when few zones are active). That’s much less than even a single PSC pump will draw when lightly loaded.
Why not install a split system and skip the HX? Spacepak, Nordic, and I believe Artic all offer them.
What do you mean split system?
As opposed to monoblock. The compressor is outside, the refrigerant is pumped inside and the heat exchanger is inside.
The biggest disadvantage is that it requires someone with an EPA license to charge the refrigerant.
You did see that the CX35 will only operate down to -17F so you'll want to be sure to have some type of backup heat even after the old gas boiler kicks the bucket.
correct...that is the plan. Probably will do an on demand condensing water heater as emergency backup when and if the polaris ever gives up the ghost.
Jim5,
I'm curious about the setup. Where does the existing/backup water heater tie in? Into the buffer tank?
Could you sketch a diagram of the proposed setup?
Jamie
With the current Polaris setup, I was thinking of simply plumbing it completely outside the CX35/buffer tank setup, and isolated by manual ball valves. I don't anticipate using the polaris often. It might help me to clarify this for myself, so I'll try and draw it out this evening. Related to this I also suppose I would need to include a switch to cut thermostat current to the CX35 when the backup is engaged. Somewhat 3rd world, but I don't want to get involved in complex controls for very occasional use.
That's right DC contrarian...thanks for your help. I divided the coldest month's therm use and divided by 30. Not absolutely precise as temps could vary during that month with one or two killer cold nights. So I think backup will be required.
Really, what I'm trying to do is use up excess KW credits from two large arrays on my shop roof. I need to see what the remaining credit is after february's reading to see what I would end up paying in electricity relative to what I would have paid in gas.
I'm pretty sure I will use up my credits and end up paying about $1200-1500 electricity for the year, assuming cop 2. I know they say cop4-ish, but I simply don't believe their numbers will play out. This would be double my gas bill with a condensing gas water heater. So, I'd be putting in an expensive system, with unknown performance, and unkeep etc to pay more for heat than I pay now. It may not be a good idea all around. I'll just have to come up with a way to use up those electricity production credits. Maybe an electric car and heat pump drier makes more sense .
Heat pump water heater would be my first pick. I have a heat pump dryer in my house and I like it.
already have the Rheem heat pump water heater. Frankly, even with miniplits on the 2nd floor, some ac in the worst of the summer, and the Rheem water heater, the credits from the array are still robust...the suckers are really cranking.
Also look at an induction cooktop. I love mine.
Often the big savings is getting rid of the gas hookup altogether and shedding the monthly hookup fee.
I think you are on the right track but the CX is not quite the right unit. I would look at a smaller EVI unit from another manufacturer. These will run down to colder temps and should cover your heat load without backup.
For my setup, I have a couple of items for freeze protection.
-the unit itself comes with heaters for the plate HX built in
-my primary loop is very long so I had to add a 2nd booster pump. This runs independent of the unit so even if the AWHP faults out, the pump will circulate water. This is also on a UPS.
-installed Caleffi freeze protection valves on the unit. I'm on city water with essentially unlimited supply of cold water, if power ever goes out the valves open and allow city water to circulate through the unit.
I've inadvertently tested the pump backup. As with many things nowadays the AWHP comes with an app which is not the best designed. I've managed to pocket dial the unit off in the middle of winter. Was off for about 8h, besides the house getting cold, nothing happened. Water temp in the unit stayed around 15C.
Outdoor wood boiler folks run water outside all the time. Freeze protection valves also seem to be the norm for AWHP in Europe.
Maybe not for everybody, but I'm pretty comfortable with the setup.
Akos, what EVI would you suggest? What do you have installed, and where are you located zone 5?
There are a number out there now. Artic, SpacePack, Hydrosolar and Macon.
I run a Gree Versati sold through Dettson. Nice part about this unit is that it comes with a built in 5.6kW backup heater. Was handy for a couple of hours in the night during the recent cold snap.
Oh, I see you are likely in Canada with the Gree line...darn. With the current US government insanity buying one of these units in the USA is a non starter.
With the current non-sense the Canadian dollar is down, so a drive up north might be worth it :)
This is another thread on a pretty similar install you are thinking about. Multi part, so search there.
https://forum.heatinghelp.com/discussion/198534/viessmann-a2whp-installation-part-1
@akos,
Very interesting with the caleffi anti-freeze valves. I didn't know that existed (and I follow caleffi on YouTube!). I think thats a genius idea.
You must them have an auto fill valve from the city supply to your monoblock loop? (Ie not a traditional closed loop system on the monoblock side)
Also, I'm in a position to start looking at monoblocks for an install in Toronto. Many of the mainstream brand names have launched their monoblocks.
Given your experience with the Gree unit (and Dettson... is there another unit you would recommend or are you happy with the current unit?
Jamie
Jamie,
I have a standard closed system with backflow preventer and pressure regulator. Normally this would be shut off after the initial system fill and purge, I'm just keeping the valve for that open so it can automatically add to the loop if the freeze valves ever open.
The unit is overall decent. I picked it because the price was right and I could get local support. There are some higher performance units out there such as the new LG monoblock. They also cost significantly more.
The one shortfall of the unit is their programmable timers and controls. The basic outdoor reset function works great, but I can't use any of the programming blocks to modify it say to shift load outside of peak hours, currently going that by programming thermostat setbacks which is not as efficient. It does have the option of sensing room temperature, so maybe with that it would work better, but I can't use that for my install.
Although capable of doing DHW, I would not recommend it unless the indirect you get also has an electric heater. Once it gets well bellow freezing, COP tanks due to high temperature delta, recovery time is pretty long and house heat suffers. This would be the case for any monoblock no matter what the manufacturers are saying.
In the Boston climate you should be able to get an average COP of close to 3.
I've attached a graph of COP vs temperature delta for the Chiltrix CX34. The delta is between outdoor temperature and water temperature (in C). There are four lines, for 100%, 75%, 50% and 25% of load. As you can see, the key to high COP is to keep the delta as small as possible and to keep the load as small as possible (although there isn't much difference between 50% and 25%, it's kind of hard to tell because they only gave four data points. ) A heat pump is going to be much happier running continuously at a small delta and a low output than running sporadically at high delta and full output.
A heat pump is going to work best with emitters -- the things that put out the heat, like radiators, fan coil units and underfloor heat -- that are able to modulate their output to meet the heating load. If you have active emitters, like fan coil units, you can modulate by changing the fan speed. With passive emitters (radiators, underfloor heat) you can either modulate the flow -- variable speed pumps, thermostatic valves or zone valves -- or you can modulate the temperature.
Like most air-to-water heat pumps, the Chiltrix has built-in outdoor reset, where the user can program in a curve to adjust the water temperature depending on the outside temperature. That allows you to have lower deltas at lower loads, raising the COP further.
If the emitters can modulate, then the heat pump can detect how much heat they emitting, and match its output exactly to that. Combined with a well-programmed outdoor reset, you get the optimal COP at all load conditions.
All of this is preamble to my main point, which is that I'm skeptical of the heat exchanger setup, because it takes away the heat pump's ability to detect the actual load. So you lose the ability to modulate the output, which puts a major hit on COP.
In general, heated floors are a good match for heat pumps, in some cases they can be plumbed direct-to-load, with no external circulators or buffer tanks.
My personal feeling is the biggest mistake you can make is to over-complicate the setup.
DC, I think you are overthinking it. A plate HX is essentially a primary/secondary loop with a delta T. It will work just as well as any PS loop. Now you still have to watch design but doable and the AWHP can sense load without issues.
The important bit here is you want your space heat to essentially run as continuous flow. That means zone valves and pumps on pretty much all the time (or off only for a bit of local tempearture adjustment say in bedroom) and space heat regulated by the outdoor reset of the AWHP. A setup like this, well dialed in you'll get excellent COP. Won't be 4 in cold climate by most likely you can heat around a seasonable average of 3.
I would also be hesitant to add glycol to old EPDM pipes.
Simplest backup would be your existing minisplits. I would not spend much money anything more. Maybe an in-line electric heater or one in the buffer tank if the AWHP supports it.
Can you talk more about how the existing system is controlled? You mentioned floor temp sensing thermostats, I'm struggling to see how that would work.
There is a sensor installed in a small hole in the subfloor from the basement. !st floor only as these did not exist to my knowledge in 1988 when I installed this. Set the floor temp to the desired floor temp at the thermostat on the wall. Its the same idea as a vanilla ambient air temp sensing wall thermostat, only reads the internal temp of the wood instead of the air. In our case, 3/4" plywood and 3/4" walnut. Pretty simple control.
Thanks. So here's what I don't understand. The heat output of the floor is proportional to the difference between the room temperature and the floor temperature. If the room temperature is constant then the heat output of the floor is going to be constant, I can only see that happening if there is another source of heat for the room, I know you mentioned minisplits earlier, I could see this being a strategy to keep a constant level of floor heat at all times.
Otherwise, the room temperature has to vary as the heating load varies. In other words, the colder it is outside, the colder it gets in the room. And vice versa.
The reason I'm curious is it affects how the heat pump is sized.
This is an interesting point. Empirically we have found that the fact that the floor is running, regardless of the air temp (within reason), just that the floor is actively running, we perceive the house as "comfortable"...ie good enough. Its a radiant system. Radiant warms the people and objects, not so much the air in the room. So, air temps in the room, within reason generally can run lower than air only heat systems. Also, unlike probably most the rest of folks these days , we don't need it to be perfectly consistent...it is winter after all. It is comfortable, enough, though yes air temps vary when is very cold out. Our view is , "so what".
The assumptions as to "what is regarded as comfortable" on which the heat loss analysis is based are not necessarily our assumptions. I think the assumptions may be more accurate for a nursing home than for an active family (over statement, but you get the idea). In all the building I have constructed, heat appliances have been sized by contractors to sell product and contractors simply will not listen to the assumptions we want to work with. So I end up doing the work myself, which is a pain.
It's your house and you should get what you want. If that's what you want, you should focus on the actual heat the current system is delivering, because that's what you want to replicate. I'd be looking at measuring as accurately as possible the send water temperature, the return water temperature, the flow rate. And then double-check it by trying to measure the boiler run time on a cold day.
Since outdoor reset is built in, my understanding is that a popular way to run air-to-water with underfloor heat is to run it continuously, no zone valves or thermostats or buffer tanks. The only circulator is the one in the heat pump itself. This would give an effect similar to what you're seeing, with a bit of temperature modulation when it gets warm out.
I am almost certain I will bag the whole heat pump idea I had been working on, as a result of this chat. It simply does not make financial sense to make a major investment which may, at best, cost the same amount to run, maybe be twice as expensive to run, never pay back the upfront cost, and expose me to an unknown upkeep/repair regimen, just to use up excess KW production from the arrays. Makes more sense to use the KW in a way that saves current gas usage with smaller appliances or charge an electric car, and to increase the gas boiler efficiency, when the polaris dies. But who knows, that 35 year old Polaris does not owe me a cent. With its stainless tank if may just refuse to ever die. However, I do think the vastly oversized 100,000btu short cycling polaris which cannot modulate BTU needs, could be replaced in a way that may be more efficient, and actually quite cheaply relative to the Heat Pump I wanted to switch to. Sigh. There is an article in the Economist this week titled "Net Zero Dads"....kind of described my mindset on all this. Recreational net Zero'ing.
Yeah, in the Boston market it only makes sense to replace equipment when it needs replacing.