Air to Water Heat Pump (aka Hydronic Distribution of WBF heat)

Hello, all,

My first post, after lurking and learning (thanks much, smart posters...)

Writing about efficient distribution of heat from WB inserts to rest of home (ROH) using air to water heat pump and hydronic distribution.

Im sorely tempted to post details of my situation and early designs. Instead, I'll pose an early general question and request stories in response:

Have you considered it (or done it) Air to Water heat capture of heat from WB Insert /FP for whole-house distribution, somehow?

Cheers!

Yes, read them, but I am thinking about design a little more purposefully gone about to capture and distribute as much heat from the WBFI as possible.

I have a plan in place... should I post that for comment?

I agree that in many homes, the bother and expense is not at all worth it.

I'm a little surprised that you are down on the Air-to-water Heat pump. I hear the Geyser is a great little unit, and there are others for more aggressive applications. This application is gaining traction, albeit slowly. I am not a professional, but as a layman I am getting very interested.

In my case, and for folks in my kind of situation, FP heat to Water seems like the holy grail. For instance, my property is 3 story 4000' sq. Dutch Colonial w. nice brick veneer in Winnipeg. My heating bill is not funny. Yes, I am constantly upgrading insulation, but now I'm paying extra attention to heating plant and hydronic distribution. I am big on wood heat as a lifestyle, and see a glimmer of an economic argument forming via heat pumps to invest aggressively in wood heat.

Currently 2 Masonry FP's on 1st floor, Both on left side of house. Many French doors, 7 bedrooms, NOT open space planning, at all, and with 6 foot 1/4 sawn oak wainscoting all over and red 1/4 sawn oak floors, there won't be any new air ducts happening. My neighborhood is full of houses like this, and we pay way to much to Gas company.

I am preparing for conversion to Radiant Floor heating from Cast Iron Rad's. The lower water temperature and zoning is highly attractive. I will soon invest in modern modulating Gas boiler and indirect HW tanks.

Now I am thinking, if well designed, I can heat the entire home in winter with the heat from the FP's, largely converted to hot water though the Air to Water heat pump, distributed via PEX to all heating zones (and snow melt applications, a very big plus here.)

If I install proper Inserts w/ blowers into both MFP's, they will cook us on one side of the house. I _have_ to move this heat. I can distribute some heat to rest of 1st floor with Air movement, but 2nd and 3rd stories are a bust (largely) as is basement.

Installing WB inserts (Likely Don-Bar) into MFP's with Ash dump blowers and reversible fans is being investigated. Negative pressure and healthy flu is biggest concern, but I think we have the problem it licked. Blower fans will reverse on Temp. reading in FP rooms reaching target. Air from other rooms will be supplied by some existing venting (and rooms are 600 and 700 sq. feet with high ceilings.) We should be good on the flu's.

If we can divert heated air directly from FP's to Heat Pump, the efficiency of Heat Pump will go way, way up. So much so that, if my math is correct, a fairly modest HP unit can provide DHW (year round, a very big plus) and much of winter's Hydronic heating at low temp.'s for the entire house.

My heating engineer friend said 'dude, why not a hydronic heat exchanger right at the FP'... we all know why not (I still need insurance.) But hot air, via the heat pump, this my insurance company will not be able to nix.

So the upshot is that, by diverting the excess heat from the FP's to the heat pump, the 'why would you heat pump hot air that you already paid for..." argument is solved.

Definitely poke holes in my plan if you see them, or, if you like this idea, feel free to add notions or experiences.

Quick reply: I cannot speak for Don-Bar, of course, and I don't even have the unit yet. But the option to divert the air stream seems to function something like a secondary burn / air wash, and allows one open it up for an open fireplace experience (which my family loves.) I do hear they kick off a _lot_ of heat for their size.

I am especially concerned with mixing the value of the romance and ambience of the insert with the value of the functionality of the Wood burning boiler (oh and yes I certainly did look at the WBB's... but they aren't getting my evening family time / romance quota filled.)

Working on your request for schematics / numbers (I'm early on, but the request is motivating.) Thanks for your repsonse!

Benjamin, low temp Cast Iron I had not thought about enough (I'm insulating all walls with Injection, so they would end up being 'oversized'.)

My boiler is a Weil-Mc Series 12 Size 7 @ 174000 output. I'm used to the Rad's running hot, or not running, with nothing much in between.

If I can drop the temp significantly, and use the TRV's, then instead of a second insert w/ heat pump and low-temp. in floor, I could use an outdoor reset unit to control the WM boiler better (?), and get that water temp way down.

My biggest deficiency is not knowing enough about this big old boiler, and having unfortunately contracted a firm that is pretty hard to deal with. It is only 10 years old, so lots of love left in the boiler.

Will the boiler be negatively affected by running the water temp. @ lower heats, do you think?

Stuck at the COP for the Insert.

The Highest Air Temp. numbers I find go up to 30 Degrees Celsius.

Does anyone have access to COP table with higher input air values (ie. something likely to be seen with air directly blown from a fireplace insert?)

Hi, slowsuzuki,

Sorry if I have been too vague.

With some fireplace inserts, there are blowers that heat air surrounding the firebox, and blow it into the room. In some conditions, there can be too much hot air available to that room. We could simply turn off the blower, but I feel that would let a lot of valuable energy up the chimney. I plan to run these inserts a lot, so it is a lot of energy.

I am proposing a blower which, by blowing from a fan in basement through a vent in the ash dump and out louvres on sides of inserts, can (under the right conditions) reverse the blower to deliver this very hot air to very near to the air source heat pump intake instead of to the fireplace room. I believe that the COP at these temps would be very high, although I do not yet know how high. I may need to find out in a real trial.

In my application, I am looking to install radiant floor heating (for a number of reasons), and deliver as much of this over-abundance of heat from our inserts as possible (I have 2 inserts in bottom left corner of home) to the rest of the home. In a large home, with very long cold winters, a $5500.00 per year annual heating bill is the baseline.

When no excess from the fires are available, the boiler has the whole task with very little (if any) support from the heat pump.

I'm already looking at replacing or modifying a great deal of this 1913 home's heating and DHW systems. I thought (still think) that finding a connection between the new inserts' excess heat and an air source heat pump could make economic sense.

AFIAK, one cannot get insurance for their home in North America if they have a hydronic heat exchanger on the Fireplace itself like they do in Europe. Air exchange seems the only viable solution.

As much as I love my city, I'm afraid this is the downside (well, that and mosquitos being our Provincial bird...) The heating days figure is at 5900 (calculated in Celsius.) Highest for a 'southern' Canadian city (take that, Edmonton...).

Benjamin, you are right, there is plenty of room for improvement, and my banker and Manitoba Hydro can attest to our dedication to improving. Bought low, with all parties knowing this project was inevitable part of the price. The walls are 'air insulated', and the unique brick veneer outside and interior wainscoting inside meaning polyurethane injections on an epic scale (DIY). All three attics are now done, Footings almost done, and I have started on the walls (aggressively, with pictures available...)

Now the inserts are about more than just heating. They are a quality of life thing, and 2 high quality 'romantic' fireplaces have good value on their own apart from practical heating. Absolutely, both the boiler and the DHW heater are on the upgrade list (modulating Gas boiler, outdoor thermal resets, indirect fired DHW. and highly zoned). The energy savings and Rebates should (at least mostly) pay for the system upgrades and insulation within about 10 years. The added value to the home is _truly significant_, most importantly because it reduces the yearly costs famously associated with such properties.

The Cast Iron Rad system is so much better than forced air (I believe), but not nearly as good as radiant floors. I gain back massive amounts of 'normally usable' square footage with radiant floors by removing monstrous rad's, and I am replacing the 2nd and 3rd floors with new hardwood anyway (1st floor joists are accessible via basement.) I definitely looked at Thermostatic valves last year, but decided to wait and do it 'right' with radiant floors retrofit. Not to mention the much lower temps. give me interesting flexibility with the proposed system over high-temp. rads.

Slowzuki, you are right on about flu temps of course, and I believe there must be two thermostats involved in the activation of the Ash dump blower fans. One just behind the insert (to maintain the required temp. for optimum fire and flu operation) and one in the room (to tell the motor to when reverse and send to heat pump.) I am making sure that we _do not develop negative pressure_ if the fans reverse (the biggest hurdle that must not fail.) The cubic foot calc. and old forced air vents in one room from past system should do the trick on that front.

And if I could vent this air to the rest of house to good enough effect, I would. But I can't. Lots of people like me can't (but wish they could...)

All things considered, I have decided against planning for Geothermal or solar as the 'green (and cheap?) energy sources' in favour of wood fire and air source heat pump as described.

Regarding the matter generally: Air Source heat pump in Winnipeg (and similar climates) is as useless for heating as one could possibly imagine (why reclaim paid-for heat?? there isn't any in the outside winter air most of the winter, I assure you.)

UNLESS:

a. one has a source of low-cost heat with an abundance of excess and wasted energy (literally up the chimney...)

and

b. one has a modern (hydronic) storage and distribution system for rest of house and DHW, and a need for cooling and dehumidifying in the warmer months.

and

c. one has the fiscal argument in favour of the initial investment (ie. Northern climate + Urban high sq'. + high number of occupants)

In such a case, the ability to capture, store, and very efficiently distribute the excess heat from the fireplaces in winter is possibly the 'holy grail' for this small but important class of homes (important because they are currently _not green_.) Compared to Solar (my, aren't those attractive...) or Ground source, high efficiency fireplace inserts w/ air to water HP add value above and beyond the fiscal payback.

The COP for the heat pumps seems to be, @ 31 degrees Celsius, 6.5. There is a fairly steady rise in COP of approx. 1 for every 10 degrees from 0, and I assume (no data to back it yet...) that rise continues to the temp. of the air coming from the Fireplace blowers.

I'll keep working on this, but for now, I have to crawl under the library and cut the old radiant floor system off the joists (literally a cast iron rad attached to the joists causing sag in floor... sigh.)

My bad, slowzuki, I am putting the heat pump in the basement! Should have stated that more clearly.

You are right of course, if it were outside, that would be... strange to consider.

The heat pump would be located very near the FP's, but one floor down in the basement, very near the Storage. The blower vents would be short, and directed right near the heat pump intake.

The waste heat I am thinking about is when I turn the blowers off because, with 2 FP's running on one side of house on main floor, it will simply be too hot in that area to run the blowers. So I'll turn them off, which lets the air escape up the chimney...

If I'm going to run one FP (carry wood, etc.), it is trivial extra effort to run both. I'd much rather use the 2nd insert 'extra heat' to heat hot water and use it variously.

I really, really wish I could by-pass the air-to-water step and stay in the hydronic loop as you suggest. That was what I had planned to do, and heating engineer friend offered to help design heat exchangers. But I need insurance, and until I hear otherwise, a hydronic heat exchanger behind the FP is a no-go insurance wise.

Isn't it??

Well, close. Yes, the basement will heat up some, which is not a terrible thing. My work shop is down there, as is laundry room. But with the blower vent directed to the Heat Pump, a significant portion of the heat will be likely be captured and stored in water.

I was kinda hoping to hear from someone who had actually considered or effected something like this. Maybe no-one has.

I'll try is out, and then report (hopefully something positive....)