DHW Production - Equipment Recommendations

SENWiEco

Hi All,

Thanks for all the help from many of you back in Feb when I was designing my radiant ceiling panels. I tried to pay forward with others posts where I was able.

I could now use some advice on equipment selection for DHW production.

For a quick recap, my ultra insulated and air tight 5000 sqft conditioned space home has a heating and cooling load below 20K Btu. We will be running 85ºF heating and 667ºF cooling supply water to radiant ceiling panels. www.theenclosure.ca for more details if interested.

The space conditioning loads will be serviced by an air source to water heat pump. I am currently looking at units from ThermAtlantic and Nordic.

I now need to figure out how to heat the DHW and am finding this has become more of a challenge than the space conditioning system.

My building design, and already completed exterior envelope, do not allow for any new unplanned penetrations. I currently only have sleeves poured into the foundation to accept refrigerant lines from the outside heat pump(s).

The dwelling is not serviced by gas and more importantly it would be impossible at this point to install flue exhaust ducting for a gas HWT or ducting needed for a Hybrid HWT (to prevent it from over cooling the interior space).

While we could do 100% resistance HWT, this would have a very high operating cost as we do not have time of day discounts. We do not get enough sun for Solar Thermal system (think weeks without sun during winter and early spring).

The Nordic ATW-45 heat pump could potentially also create DHW by using their desuperheater stream, but this would be pushing the equipment, would require three tanks (including space conditioning buffer tank, a preconditioning and final DHW tank), and during the shoulder spring and fall months, the heat pump would ONLY be running to create DHW, in which case we are not sure it could run long enough to allow the final tank to come up to the required 140ºF (preconditioning tank would potentially reach cut-off before final would reach 140ºF)

The ThermAtlantic DX2S-2 would have no means of directly contributing to the DHW production.

I looked at Hybrid HWT's, but as above, do not have ability to duct them to exterior and I do not have a non-conditioned space I could place them into. They would cool my conditioned spaces too much (up to 10ºF). They are also noisy, and my mechanical room is in basement where future owners will probably create a rental suite. So, I believe this option is off the table.

I looked at the Sanden CO2 unit, but it has pretty bad user reviews for first hour output, is $5K, and because of CO2 refrigerant, difficult to service.

Nordic have a small water to water heat pump (WD-16), also $5K, that could use the space conditioning buffer tank as its water source and would heat up the water in a 100% resistance HWT (which could be used as backup) . During the summer when in chilled water mode, it would cool the space conditioning buffer tank even further, increasing the efficiency of the main heat pump. In the winter, it Would increase the load, but again may make system more efficient by running for longer periods but at least would be increasing the load on a fairly efficient heat plant (compared to gas or resistance DHW heating).

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Do any of you know of a water to water, or split pak air to water, heat pump that can produce 140ºF and cost less than $5K (cad) ??
If air to water, I need the split pak type so not cooling or installing noisy component in interior space. I would also prefer that the exterior unit line set is refrigerant as apposed to needing a glycol mix.
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Appreciate any direction any of you can provide!

Cheers,
Sean

Zman

There are some split hybrid systems on the market. I think @Hotrod posted them a few months back.

Jamie Hall

You do have a curious problem. If it weren't for the potential noise problem, I'd look at the hybrid heat pump hot water heaters -- although I have to admit that I've had bad luck with them. The Nordic unit you mention in the last paragraph is attractive, though pricey -- but the question I'd have there is where would its mechanicals be located? Outside?

Do you have the possibility of solar collectors for DHW? Again, I'm not to keen on them but they might be an option...

SENWiEco

Hi @Jamie Hall , Thanks for follow up. We do not get enough sun for solar system. Re the Nordic unit, it would be inside. I still need to find out how noisy IT would be. But believe there is way to insulate enclosure. Agree re Hybrid HWT. I have read a lot of reviews that have not been too happy with them.

Yes DHW has been a bit of a problem. House was designed around the Daikin Altherma for combined conditioning and DHW, but was pulled from market. Now having problems finding affordable unit that can create 140ºF DHW reliably.

Thanks @Zman, I did do a search before posting and only found reference to SpacePak, but they top out at 120ºF, so not really useful for DHW

S

hot_rod

Maybe run the desuperheater to a reverse indirect. A small electric tankless for final boost. Similar to this but piped to the desuper circuit, so you have summertime DHW

Do you need 140F? For legionella piece of mind?

SENWiEco

Thanks for comment @hot_rod. Problem with the desuperheater circuit on Nordic is that it only runs of course when the main circuit is running. So the issue is more the 6-9 months of shoulder seasons when I do not anticipate needing ANY space conditioning in the dwelling. During this time both the main and desuperheater circuit would need to run long enough periods to create any significant volume of 140ºF. Yes the 140ºF is to combat any bacteria risks. I am also trying to stay away from the running costs for resistance heaters as we do not have time of day discounts. I am about $0.13/kWh.

hot_rod

The desuperheater works in either mode, certainly if the HP doesn't run it will not produce DHW, so a plan B is needed.

A engineer friend met with Nordic's engineer a week or so ago and was impressed with the product and company.

SENWiEco

thanks @hot_rod. Do you know of any other affordable water to water heat pumps capable of 140ºF? Something from the ground exchange industry?

hot_rod

I don't know much about heat pump water heaters. Pros and cons, slow recovery and they sometimes kick to resistance mode from what I hear. Expensive and more moving parts compared to electric resistance tank.

How much DHW do you consume? For the cost difference maybe an electric water heater, an efficient well insulated model, will pencil out the best for those "off season" periods?

There should be a way to use an indirect with electric element, like a solar tank. HP does the load when possible, element tops off temperature, or 100% when HP is off line.

SENWiEco

I have calculated a 92gal first hour draw for the dwelling. Thanks for your follow up.

hot_rod

probably 4- 500 bucks per year for DHW at .13. Really depends on how much you need or want per day, month, etc

hot_rod

Now deduct for the cost and % of the year that the HP could contribute at higher efficiency

SENWiEco

I am inclined to now look at 100% resistance HWT per advice from @hot_rod. No new heat pumps have been added to my radar via this thread, and the Nordic WD16 has a sound rating of ~55.5 dBA at 3ft. I am thinking that would be far too noisy in my air sealed house.

SO - how do I go about estimating the DHW heating costs for a dwelling suitable for 5 people? What parameters do I need to calculate this. I search the archives but did not find anything on this under the DHW section.

I do know that the municipal entering water temp will be 40F at the coldest point of the winter and about 60F at the summers hottest point (I have over 400 temp readings for the supply water from the muni for a 1 year period)

Secondly, what is recommended as the best well insulated electric resistance HWT. Looking for something that will have about a 92gal first hour rating and want as low as possible stand-by costs.

Advise much appreciated.

hot_rod

Water heater manufacturers have charts and tables to help estimate use and operating cost It can vary depending on how a family uses water. Showers or tubs, how much laundry, dishwashing, etc

your calculation will be complicated by how much and how often the heat pump can contribute to some or all of your DHW loads

First step is to measure or estimate how much hot water you use, that directly relates to cost to generate

The Marathon composite tank gets good reviews around hear for efficiency, not sure about performance

Additional WH blankets can be added to electric tanks to reduce standby loss

Jean-David Beyer

Could solar take the chill off the municipal water so that whatever additional heating you need would have less work to do? When I had an oil-fired boiler and an electric hot water heater, I ran the municipal cold water through the (unused) water heating coil in the boiler and into the cold water input into the water heater. The boiler normally ran around 145F to supply radiant slab at grade.

SENWiEco

Hi @Jean-David Beyer, we get very little solar energy during the winter and spring. I am putting solar PV panels to try and extract as much energy as possible yearly. I will also look at drain heat recover to help some.

SENWiEco

Thanks @hot_rod. The problem is that the heat pump will not be running at all for probably at least 6 months of the year due to my really low heating and cooling loads. Thanks will look at Marathon tanks and estimated operating costs (yes I understand highly variable - just looking for a rough idea)

Larry Weingarten

Hello, An old rule of thumb is 20 gallons of hot water for the first person and 15 gallons per day for everyone else. I'd be looking at low flow fixtures, (particularly the showerheads) I'd be looking for pressure compensating fixtures and showerheads as well. From there, if you can still do this, use the smallest diameter hot water piping you can get away with, and still get decent flow. For example, 3/8" tube holds about half the water that 1/2" tube does. If you have adequate pressure, physics tells up that 1/4" tube will work for some things! This speeds up hot water arrival and cuts water and energy waste. Adding good insulation will give you more time between draws, by keeping the lines hot. If things are really spread out, using a demand controlled recirculating pump will help too.

Yours, Larry

SENWiEco

Thanks @Larry Weingarten Do plan to look at reduced tube sizes and will be insulating all lines. I will increase the gallons per day as there are some bath people in the house.

jumper

It may be a little late but your idea of drain water to DHW can be economic. Especially if you can configure for superheat recovery and subcool extraction. Why do you require 140°?

SENWiEco

140 is required to safely store potable water. It then needs to be mixed down to 120 for faucet supply.