Hydronic Floor pump frequency vs water supply temp? - Page 2

AC_Hacker · 12-24-12, 09:36 PM

From what I am reading here, you are pretty much 'bought in' to 140F water because you are using the same heater for both domestic water and heat, am I correct?

Vlad (near Vancouver, CA) has a system like the one you are envisioning, but he has a 'smart' controller that injects metered amounts of hot water into the system as required to maintain the house temp. As I recall, his controller takes temperature readings from the air temp of the house and also outside air temp. I think it also measures water temp going into the floor and also coming out from the floor. From all this info, it is able to calculate the heating power of his system and the total resistance due to thermal mass. With this done, it can meter the heat input into the system, at appropriate rates, to manage various heating and cooling gradients so the house temp stays even.

Regarding system efficiency and floor temp, etc, the hydronic heating industry is coming out of an era of cheap fuel and entering an era of ever more expensive fuel. The 'common wisdom' of the last 60 years is not relevant as it once was.

Europe, because energy costs are much higher than in USA & Canada, has embraced high efficiency radiant heating, they have also embraced high efficiency insulation (to keep the heat in the house). As a result, the amount of heat required to heat a modern European home (especially in Scandinavia & Germany) is much less than in USA & Canada.

So we should pay close attention to their approaches, and learn as much as we can before we start laying PEX.

Best,

-AC

Mikesolar · 12-24-12, 09:58 PM

The really good builders with heat pumps in Europe are using 100-150mm (4-6") spacing which is about as good as you can get. Tubing is cheap and a closer spacing benefits any heat source.

Daox · 12-25-12, 07:55 AM

Are they using heat spreaders at those closer spacings?

Mikesolar · 12-25-12, 08:02 AM

Nope, the Europeans generally only use a thermal screed, 75mm+, for the tubing. Aluminum plates are a North American thing as we build on wood frame and most houses over there were concrete or other thermal mass.

AC_Hacker · 12-25-12, 12:47 PM

Quote:

Originally Posted by Mikesolar

...the Europeans generally only use a thermal screed, 75mm+, for the tubing...

Any more detail regarding what 'thermal screed' consists of?

Thanks ...interesting stuff.

Best,

-AC

Mikesolar · 12-25-12, 01:04 PM

It could be anything from a sand based mortar mix to gypsum cement (Gypcrete, which is what I use over wood floors). There are lots of self leveling products available some of which can be mixed in a large garbage pail. I don't see any reason to use a heat emission plate when you can use a thermal mass. Sure they heat up faster but the thermal mass holds heat better and can take a wider range of input temps and moderates temp swings better.

Drake · 03-08-13, 10:39 PM

Related to this I am trying to compare suppling a constant low temp flow by on demand heating vs batch heating a stored supply of high temp water and mixing it for a high mass/low temp floor. Either way I plan to have at least two heat sources in the system for back up. As I it will be in a smaller super insulated passive solar space the heat demand will be on very low side. Pay back for a super tech system will be minimal. I do have off peak elec and will be grid tied and plan to have PV and wind to bank elec credits.

Mikesolar · 03-09-13, 05:59 AM

low heat load homes create issues when picking a heat source. Any traditional boiler (or furnace) start at maybe 40-50Mbtu or often bigger and your house could potentially need 10-15Mbtu at design conditions. This means that any fossil fuel boiler will always be running at minimum when it is -20C (-4F) out. So, if you need to use gas, it is best to use something like a high efficiency water heater (polaris or similar). I don't like using a regular gas water heater because they are still only 50-60% efficient and they don't use outside combustion air.

That leaves either an electric boiler or a heat pump to heat water or just a ductless split, if the space is open enough. Combined with a wood stove (which will overheat the space really fast) and/or solar preheat, you will have the most effective backup to passive solar that you can have.

Most of my systems use constant flow floor heating with a 3 way mixing valve on an outdoor reset control. This usually comes from a tank which needs to be set 5C+ higher than the desired floor temp for the mixing valve to work properly. I don't use an internal t-stat except as a high temp limit any more. The control will also shut off the floor when the outdoor temp hits a desired temp, which for me can be 18C.

MN Renovator · 03-09-13, 09:44 AM

Regarding the installation of a variable boiler for hydronic floor heat. What is the cost to install all of what is needed for hydronic floor heat from scratch in comparison to forced air? I remember going through various trade based stuff for homes under 20k BTU requirements where they found it was universally cheaper to go with a condensing water heater tank with forced air using a hydronic coil.

Mikesolar · 03-09-13, 10:12 AM

Quote:

Originally Posted by MN Renovator

Regarding the installation of a variable boiler for hydronic floor heat. What is the cost to install all of what is needed for hydronic floor heat from scratch in comparison to forced air? I remember going through various trade based stuff for homes under 20k BTU requirements where they found it was universally cheaper to go with a condensing water heater tank with forced air using a hydronic coil.

That's a good question. This is just my opinion but I see forced air as a lower quality heat system to start with and if you look at the efforts taken to control humidity, dust and pathogen movement, radiant heat wins every time BUT, it can be more expensive. Of course, you still need fresh air so that becomes the tradeoff. If I had a 20Mbtu heat load in a 2000ft2 house, I would not need to fill every area with tubing to meet the heat load so the cost could be quite low but it is quite dependent on the home design.

If you have a ranch, slab on grade house, I could do it cheaper than ducting, especially if you take into account the bulkheads and extra drywall work necessary for it. HRVs could be done without ductwork using the German Lunos products.

In the end, if the ductwork and coil costs $5k installed I am sure the floor heat could be done for $6k and with less noise, service, dust etc.

12-24-12, 09:36 PM	#11
AC_Hacker Supreme EcoRenovator Join Date: Mar 2009 Location: Portland, OR Posts: 4,004 Thanks: 303 Thanked 723 Times in 534 Posts	From what I am reading here, you are pretty much 'bought in' to 140F water because you are using the same heater for both domestic water and heat, am I correct? Vlad (near Vancouver, CA) has a system like the one you are envisioning, but he has a 'smart' controller that injects metered amounts of hot water into the system as required to maintain the house temp. As I recall, his controller takes temperature readings from the air temp of the house and also outside air temp. I think it also measures water temp going into the floor and also coming out from the floor. From all this info, it is able to calculate the heating power of his system and the total resistance due to thermal mass. With this done, it can meter the heat input into the system, at appropriate rates, to manage various heating and cooling gradients so the house temp stays even. Regarding system efficiency and floor temp, etc, the hydronic heating industry is coming out of an era of cheap fuel and entering an era of ever more expensive fuel. The 'common wisdom' of the last 60 years is not relevant as it once was. Europe, because energy costs are much higher than in USA & Canada, has embraced high efficiency radiant heating, they have also embraced high efficiency insulation (to keep the heat in the house). As a result, the amount of heat required to heat a modern European home (especially in Scandinavia & Germany) is much less than in USA & Canada. So we should pay close attention to their approaches, and learn as much as we can before we start laying PEX. Best, -AC __________________ I'm not an HVAC technician. In fact, I'm barely even a hacker...

12-25-12, 07:55 AM	#13
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Are they using heat spreaders at those closer spacings? __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

12-24-12, 09:58 PM	#12
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	The really good builders with heat pumps in Europe are using 100-150mm (4-6") spacing which is about as good as you can get. Tubing is cheap and a closer spacing benefits any heat source.

12-25-12, 08:02 AM	#14
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	Nope, the Europeans generally only use a thermal screed, 75mm+, for the tubing. Aluminum plates are a North American thing as we build on wood frame and most houses over there were concrete or other thermal mass.

12-25-12, 01:04 PM	#16
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	It could be anything from a sand based mortar mix to gypsum cement (Gypcrete, which is what I use over wood floors). There are lots of self leveling products available some of which can be mixed in a large garbage pail. I don't see any reason to use a heat emission plate when you can use a thermal mass. Sure they heat up faster but the thermal mass holds heat better and can take a wider range of input temps and moderates temp swings better.

03-08-13, 10:39 PM	#17
Drake DIY Guy Join Date: Jan 2011 Location: Mpls,MN Posts: 315 Thanks: 2 Thanked 17 Times in 17 Posts	Related to this I am trying to compare suppling a constant low temp flow by on demand heating vs batch heating a stored supply of high temp water and mixing it for a high mass/low temp floor. Either way I plan to have at least two heat sources in the system for back up. As I it will be in a smaller super insulated passive solar space the heat demand will be on very low side. Pay back for a super tech system will be minimal. I do have off peak elec and will be grid tied and plan to have PV and wind to bank elec credits.

03-09-13, 05:59 AM	#18
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	low heat load homes create issues when picking a heat source. Any traditional boiler (or furnace) start at maybe 40-50Mbtu or often bigger and your house could potentially need 10-15Mbtu at design conditions. This means that any fossil fuel boiler will always be running at minimum when it is -20C (-4F) out. So, if you need to use gas, it is best to use something like a high efficiency water heater (polaris or similar). I don't like using a regular gas water heater because they are still only 50-60% efficient and they don't use outside combustion air. That leaves either an electric boiler or a heat pump to heat water or just a ductless split, if the space is open enough. Combined with a wood stove (which will overheat the space really fast) and/or solar preheat, you will have the most effective backup to passive solar that you can have. Most of my systems use constant flow floor heating with a 3 way mixing valve on an outdoor reset control. This usually comes from a tank which needs to be set 5C+ higher than the desired floor temp for the mixing valve to work properly. I don't use an internal t-stat except as a high temp limit any more. The control will also shut off the floor when the outdoor temp hits a desired temp, which for me can be 18C.

03-09-13, 09:44 AM	#19
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	Regarding the installation of a variable boiler for hydronic floor heat. What is the cost to install all of what is needed for hydronic floor heat from scratch in comparison to forced air? I remember going through various trade based stuff for homes under 20k BTU requirements where they found it was universally cheaper to go with a condensing water heater tank with forced air using a hydronic coil.