Best way to heat hydronic closed loop system

dousterhout

Newbie here. I am building a new house with concrete slab for walk out basement and concrete main level on metal pans, 2000 sq ft per level. I plan to put 1/2" pecs on both levels with 8 total zones. I have manifolds built and pressure tested and will soon be laying pecs.

I need help with what to use to heat to the closed loop water, as well as the water for the house? I will have a solar array for electric that will offset any electric usage and would like to NOT use propane, if that makes sense.

I am also struggling with tank or tankless?

I live in central VA.

Any suggestions are greatly appreciated.

Dean

Alan (California Radiant) Forbes

There are many condensing boilers to choose from; Viessmann, Lochinvar, IBC..........I would ask your local suppliers which one they recommend and support.

As far as domestic hot water (DHW), you have a fairly large house and I would use either an on-demand water heater or an indirect which uses your boiler as a heat source. On-demands are good if you have a large capacity bathtub that you can't possibly fill with a conventional tank-type water heater, but I prefer indirects for many reasons.

You must already know the heatloss of your house and spacing of the PEX since you've already installed your manifolds.

Jamie Hall

If you don't want to use propane, what other fuels do you have available? Natural gas? Oil is always available, of course.

If you have photovoltaics on the roof, you probably don't have room for solar thermal collection. Otherwise, I would suggest that since you are creating a high mass -- and high thermal storage -- system, which would even out, to a great extent, the variations with sunlight. You could use that with a properly sized condensing gas boiler, such as @Alan (California Radiant) Forbes suggested. Without that, I'd still go with the modulating condensing gas boiler.

I'd probably use an indirect off that boiler for domestic hot water. Again, though, if you have natural gas there is much to be said for tankless water heaters for domestic hot water -- but be careful to select a unit which can accommodate your peak demands.

dousterhout

Thanks for the feedback Alan. Actually, I have the manifolds ready to go, but have not installed in house. I have a separate discussion on calculating heat load.

Yes, the house is big, but the reality is that just my wife and I will be there 99% of the time. The downstairs will only be used for my shop, a yoga room, and the rest will hardly ever be used.

So is electric an acceptable source for heating for hydronic pecs?

dousterhout

There is not natural gas available, however, I can do a propane tank if electric is a really bad idea. The thought behind the electric is that I will already have a grid tied electric Array that can offset, or eliminate, the electric costs.

The big question is .... is electric a resonable option... or a really bad idea?

Thanks for the help.

kcopp

Need to ask your PV solar installer how much output the array can handle. Electric heating w/ chew up a good amount power in the winter. Unless you spend a good deal of money to super insulate and tighten up the thermal envelope I am not sure that will be a good choice.
You can however prepare to install PEX tubing and decide on fuel choice after you get a heatloss done and the info for your PV array.

Jamie Hall

Direct solar space heating can, with some care and thought and ingenious design and very tight superinsulated structures, be made to work.

Photovoltaics, no. Not with current technology. You will -- even with a big array (like the entire roof) -- be drawing more power from the grid than you will generate, possibly a lot more. Regrettably, that's just the way the numbers add up.

That said, there are good electric boilers made. To use one, though, you would have to have adequate electric service (I was just looking at one; 138,000 BTU, running on single phase 240 volt, at 113 amperes) (just to illustrate the problem with photovoltaics in that regard -- that's a bit over 40 KW. Which, with current generation PVs would require 200 square meters of array or 2000 square feet -- but only when the sun was shining).

Jellis

You may consider a hybrid electric water heater.
uses heat pump technology to reduce electricity usage. Would be a great low cost solution for your domestic hot water since you have the solar collectors providing power for it.
This would allow you to get a smaller unit for heating.

bob eck

What about geothermal HP?

GroundUp

Let's say, for the sake of argument, that your total heat loss at design temp is 80,000 BTU. That's 23.45kW per hour of electricity needed to heat the space at design temp. You'll be grid tied, so it's not the end of the world if your PV array can't keep up, but let's say that design temp hangs around for 24 hours and there is no PV gain from the panels. So you'd need 562.72 total kW for that 24 hour period. 562.72 kW at 10 cents is $56.27 in electrical consumption in just one day. Now let's use that same scenario with LP. 80,000 for 24 hours makes 1.92M total btu for the same 24 hour period at design. At 90% efficiency, which is easily attainable with low temp radiant, that would use 23.41 gallons of LP. If LP is $1.50/gal like it is here, it cost you $35.12, a 39% savings over electric. Of course these numbers will vary depending on prices in your area, but it's a good starting point to consider. At the same time, a good electric boiler is almost always less costly to install and maintain than a gas boiler. Not enough to make up for the gap in fuel costs, but also something to consider. If it were my home, with the $.14 electric rate and LP prices typically in the low $1 neighborhood during pre-buy, I'd strongly consider a ground source heat pump with an LP backup. But that's just like, my opinion, man

Solid_Fuel_Man

It really boils down to what you want to use for energy, and how much that will cost.

I bet in VA coal is pretty cheap....but the mess is BAD and most wouldn't go that route

Electric rates? Generally resistance electric is the cheapest to buy and install, but the most expensive to operate. This is for electric resistance heat, a ground source heat pump may very be the best option for your moderate climate. Here in ME they dont work out so well!

Wood, wood pellets? Again depends on the amount you want to be involved with your heating system.

Propane? If you go that route, buy your own tank. The initial expense will far outweigh the savings and freedom to shop around. Avoid underground tanks as they are very expensive in all aspects.

dousterhout

Wow... a lot of very thoughtful analysis... thanks all for taking time to help with our challenge. Let me ponder the information so that hopefully when I come back with some more questions you will feel like I listened and tried to understand.

I have to say that I am used to less than $10 per day for heat and electric, so the idea of $50, or even $30, per day is very scary.

We are going to spend most time upstairs so downstairs can stay in the 50-60 degree range. Upstairs we will have a wood burning fireplace and we love fires which will also have fans and vents to throw heat into the great room.

Solid_Fuel_Man

Oh! Wood heat! Dont start me on that path!

There are many options to burn wood at the highest efficiency and really surprise yourself at how little wood it takes to heat an entire structure. Think that likely your fireplace if it's an old fashioned open hearth is about 20% efficient. If it's an insert likely around 40-50% efficient. A wood gasification system is 75-85% efficient, so by numbers alone you can be getting 2-4x the heat out of that wood than you are now.

I'll halt the rant.....

SuperTech

Ground source/water source heat pump would work out the best for you. Next best option would be a modulating condensing propane fired boiler.

dousterhout

Is the heat load calculation the amount of BTU's required to maintain the existing temperature per day? I am trying to understand if the house needs 80,000 btu per day (although I do not understand how outside temperature plays into this) how much propane would it use and how much electricity would it use and the do the cost analysis?

ch4man

dousterhout said:

We are going to spend most time upstairs so downstairs can stay in the 50-60 degree range. Upstairs we will have a wood burning fireplace and we love fires which will also have fans and vents to throw heat into the great room.

bad idea. your building a high mass radiant system. you cant do deep setbacks. it'll take all day to recover from 50-60 degrees.

why the aversion to propane?

delta T

dousterhout said:

Is the heat load calculation the amount of BTU's required to maintain the existing temperature per day? I am trying to understand if the house needs 80,000 btu per day (although I do not understand how outside temperature plays into this) how much propane would it use and how much electricity would it use and the do the cost analysis?

No, the design heat loss is Btu/Hr. However, outside temp plays a huge role here. The heat loss of the structure is proportional to the difference in temperature between the outside and the inside of the structure (often called 'delta T', delta being a greek letter that looks like a triangle often used to denote difference or change). So, if you have a heat loss of 80,000 Btu/hr at an outside temp of -10 and an inside temp of 70, you have an 80 degree delta T. The same structure, at the same inside temp will have a 40,000 btu/hr heat loss if the delta T is 40 degrees or (30 degrees outside, 70 degrees inside). The design load is rarely ever met, and most of the time the real heat loss will be significantly lower than your design day worst case scenario. Hope that clears it up a bit for you. Always keep in mind that the exact outdoor and indoor temperatures don't matter so much, just the difference between them.

dousterhout

CH4man. Our house is two levels, with the lower level in the ground and a walkout basement. We will be living on the upper level and not downstairs very often, so we could (not saying we should) keep the downstairs at lower temp, say 50-60 and have the upstairs at 70 . The fireplace is upstairs. We would NOT try to change the temp but would always keep it the same and leverage the thermal mass. That is why we are spending the money for the concrete upper level.

Question: Should both levels be kept at same temp or is it ok to have one level at a lower temp and the upper level at a higher temp? Does that hurt the effectiveness of the thermal mass?

The only reason for not doing propane is simplicity with just having one power source and the fact that I want solar PV and once installed it offsets usage. I am just exploring the option to see if it makes sense. If it doesn't, then we can go the propane route. If electric were to cost a little more but my PV solar would pay for it, then electric might be the better way to go. If electric is going to cost "a lot more", then propane makes sense.

There are several good reasons to use propane, seems to be more efficient for heating, if no electricity, still have gas stove and hot water for heat and bathing.

One thing I am still confused about is some articles say that both methods use energy to heat and at the end of the day it is the relative cost of electricity vs cost of propane that determines which one is better cost wise. I am struggling to find an equation for fitting that into the discussion of the HeatLoad???

Jamie Hall

It's a little tricky -- but not that bad, really. A heating device drawing 1 kilowatt will put out -- very roughly -- 3000 BTUh. If you ran that device for 24 hours, that would be 24 kilowatt-hours of electricity (what the power company charges you by) and about 72,000 BTU. That would be, if you were burning propane, about a gallon of the stuff. Which is what the propane company will charge you by. From that you can compare the relative costs pretty easily. No need to go into more exact comparisons.

Now to look at a specific case, your heat loss figure can be used to determine, on any given day, how much heat you need (BTU or kilowatt-hours), if you want to.

Converting back from your heat loss to kilowatt-hours, you can begin to figure whether your photovoltaics will come close. A generally accepted average in the northeastern US and eastern Canada is that you will generate some power about 12 percent of the time.

dousterhout

Thanks Jamie, is heatload calculation based on a set difference between outside and inside? If heatload is BTU/hr and that is dependent on outside and inside differential, what is the standard from which the heatload is calculated?

Delta T referenced DeltaT and I am trying to understand that. The reverence is -10 and 80... is this standard for the heatload calc?

FYI... LP cost in VA is now at 3.07 per gallon.

You mentioned in an earlier comment a good electric boiler? Is it allowed to post that? If not, could you email it to me?

Is there a viable heat pump water heater/boiler that could be used for the radiant heat?

Zman

Your heat loss calc will give you estimated heat loss (required energy to offset the loss) on the design day. You can estimate your usage any day of the year by using HDD (heating degree day) data available through numerous weather data sites.

Don't overthink the cost of fuel. Just plug your local costs and efficiency of appliances into this sheet and Viola....

Solid_Fuel_Man

A design day is the coldest day of the year. So at say -20F you need 60,000 btu/hr to maintain 70F inside. It would be said that you need a boiler and enough radiation to produce 60,000 btu/hr.

Same example house, at 0F may only need 50,000 btu/hr to maintain 70F inside.

The colder it is outside the more energy flows through walls etc, therefore you must have more heat inside to offset that heat loss.

We are always essentially heating the outdoors. It's the insulation and building structure which slows down that heat loss. Now we can see why insulation is so important.

Jamie Hall

Design day temperatures in Virginia vary, depending on where you are, but are around 15 to 20, Fahrenheit. It is customary to use a design interior temperature of 70 Fahrenheit. This is used, in conjunction with the characteristics of the building, to determine the design day heat loss. Slant/Fin has a very nice calculator for that, which isn't hard to use.

There are a number of makes of electric boilers. At the present time they are little used in residential applications, as the cost of energy from electricity is almost always greater -- sometimes very much greater -- than getting the same energy from oil, natural gas, or LP gas. Furthermore, very few houses have the necessary electrical service (just for laughs, the main place I care for -- which is oil burning steam -- would require a 600 ampere 240 volt main service if it were heated electrically).

Heat pumps are a viable option for hot water heating, but not for steam. In your climate they are also a viable option for forced air heating and cooling.

dousterhout

Wow guys.. Thanks... this is great info. I was missing this part of the puzzle. Zman... what a great calculator... thanks.

dousterhout

Jamie, you say "heat pump is viable option for hot water but not steam". We will have hydronic radiant heat which is hot water and not steam. It sounds like that would be a viable option?

Does anyone have any thoughts as to which brands/models would be best to consider for a heat pump for the radiant heat?

pecmsg

dousterhout said:

Jamie, you say "heat pump is viable option for hot water but not steam". We will have hydronic radiant heat which is hot water and not steam. It sounds like that would be a viable option?

Does anyone have any thoughts as to which brands/models would be best to consider for a heat pump for the radiant heat?

A system that's Properly Sized, installed and maintained.

A HVAC "System" is not a appliance that you take home and plug in. It must be installed to the manufactures specifications and best industry standards.

The name on the trucks and personnel installing it is more important then the name on the boxs!

dousterhout

I have a great HVAC person to do the central air and heat. What I am missing is someone for radiant heat. Sure, I can lay lines, assemble manifolds, solder and pex... but the reason I am posting is because I need help deciding on the mechanism to provide the energy to drive the hydronic system. I do not have a local expert to help with that. I tried for several months to find someone I could work with, to no avail.

My current plan is to get all the radiant lines, manifolds, and pumps in place and have y hvac person install the boiler/heat source. Unfortunately, he can't really help with the question of which one to use?

So.... here I am.. and thanks to everyone that has graciously volunteered their thoughts and suggestions. It is sites like this that make diy possible on a very successful level.

Gordy

To the point. What is the KW producing potential of your PV array in summer and winter?

Relying on a PV array to offset electric costs is pretty unreliable, and inconsistant to budget bills accordingly.

My approach would be calculating roughly how much an all electric system would cost to operate according to the heatload calculations. Then apply worst case PV output. If the difference makes you uncomfortable. I would scratch the electric approach for heating.

Another thing to remember is PV panels degrade over time which reduces KW production.

Another thing to remember summer temp differentials for AC is far more consistent on the top end design day than winter design temps.

Solid_Fuel_Man

Grid-tie PV is a great system. You get all the benefits w/o the inefficiency of batteries as well as their maintenance and high cost.

For perspective my personal home with my wife and son and daughter, uses an average of 298KWh per month. That was the average for 2018.

I have no special appliances, a top-loader Maytag from the 80's, an side-by-side fridge from 1995 with frequently used ice maker, and a 200' deep well.

We have a gas range, and gas dryer, and do about 6 loads a week. House has plenty of glass and lights are used minimally. She works from home and is here most days.

Consider getting a properly set up fossil fuel boiler and add in an electric boiler later.

I know my utility won't pay you for excess KWh you make, only gives you credits which expire in mid winter when your need them the most assuming you didn't burn them all up for A/C.

Ben_Z

Just want to help. One of the best guides I've read on the net about tankless water heaters is this one: https://waterheaters.review/. You may find what you're looking for.

bob eck

Ben Z no attchment

hot_rod

If you go with electric for a fuel source I'd look at a heat pump, air to water to maximize the electrons.

dousterhout

I am looking at the ATW heat pumps. Anyone have any experience with Blue Ridge Company?