Best Practices in Modern Hydronic Heating - AN … · "Best Practices in Modern Hydronic Heating ... this cut would destroy the load-carrying ... • None of them look like a boiler

presented by:John Siegenthaler, P.E.

Appropriate DesignsHolland Patent, NY

www.hydronicpros.com © Copyright 2014, J. Siegenthaler, all rights reserved. The contents of this file shall not be copied or transmitted in any form without written permission of the author. All diagrams shown in this file on conceptual and not intended as fully detailed installation drawings. No warranty is made as the the suitability of any drawings or data for a particular application.

TRV

TRV

TRV

TRV

TRV

TRV

thermal storage

tank

thermostatic radiator valves!on each panel radiator

pressure-regulated!variable speed

circulator1/2" PEX or

PEX-AL-PEX tubing

panel radiator

manifold station

"Best Practices in Modern Hydronic Heating - AN OVERVIEW

2014

This Morning’s topics...• Why hydronics• High efficiency gas-fired boilers• Low temperature heat emitter options• High efficiency circulators• Homerun distribution systems• Zoning options

"Best Practices in Modern Hydronic Heating - AN OVERVIEW

What are the advantages of using hydronic heating in these houses?Water vs. air: Itʼs hardly fair...

14" x 8" duct

this cut would destroy the load-carrying ability of the floor joists

2 x

12 jo

ist

3/4" tube

Water is vastly superior to air for conveying heat

A given volume of water can absorb almost 3500 times as much heat as the same volume of air, when both undergo the same temperature change

Gas-firedboilers

Oil-firedboilers

wood-firedboilers

pellet-firedboilers

CONVENTIONALBOILERS

CONDENSINGBOILERS

Gas-firedboilers

Oil-firedboilers

RENEWABLE HEAT SOURCES

solarthermal

collectors

water-to-water(geothermal)

heatpumps

air-to-watervapor comp.

water-to-water(geothermal)air-to-water

absorp.cycle

Conventional boilers are not intended to operate with sustained flue gas condensation. Allowing them to operate with such condensation will damage both the boiler and flue.

High efficiency gas-fired boilersHydronic heat source options

gas-firedcast-iron sectionalatmospheric draft

oil-firedcast-iron sectionalatmospheric draft

oil-firedsteel fire tube

atmospheric draft


atmospheric draft

gas-firedcopper water tubeatmospheric draft

Conventional boilersConventional boilers are not intended to operate with sustained flue gas condensation

For conventional gas-fired boilers, sustained inlet water temperatures of 130 ºF or more are recommended to prevent sustained flue gas condensation.


atmospheric draft

“EVERY BOILER can be a condensing boiler...”Conventional boilers


atmospheric draft

The system must be designed to maintain the boiler inlet temperature above dewpoint of flue gases.

VENT

boiler inlet temperature!

sensor

mixed supply temperature!

sensor

mixing!assembly

conventional boiler

boiler loop

distribution system

Conventional boilers

The only way to ensure that a conventional boiler is protected against sustained flue gas condensation is to measure boiler inlet temperature and provide a mixing assembly that reacts to this temperature.


atmospheric draft

An intelligent mixing assembly that can sense boiler inlet water temperature and react to it WILL protect the boiler from sustained flue gas condensation.

Protecting conventional boilers from sustained flue gas condensation

The only way to ensure that a conventional boiler is protected against sustained flue gas condensation is to measure boiler inlet temperature and provide a mixing assembly that reacts to this temperature.

50,000 Btu/hr!heat input rate!

to water

135.4 ºF!20 gpm

130 ºF!20 gpm

6 floor circuits!300 ft x 1/2" PEX!

12" spacing bare slab

mixing valve!controller !

set for 125ºF

50,000 Btu/hr!heat output rate

111.4 ºF!5.5 gpm

93 ºF!5.5 gpm

thermal equilibrium

93 ºF!2.39 gpm

bypass flow through!closely spaced tees

14.5 gpm!135.4 ºF

135.4 ºF!2.39 gpm

bypass!circulator

130 ºF

135.4 ºF

∆T=5

.1ºF130 ºF

dewpoint

boiler inlet temperature sensor

93 ºF3.11gpm



atmospheric draft

These boilers use stainless steel or aluminum heat exchangers that can withstand the corrosive nature of condensed flue gases. (pH ≤ 4.0)

Mod/con boilers use a variable speed combustion air blower and proportional gas valve to regulate the rate of combustion. Typical range of modulation (20 - 100%).

• Wall hung• Free standing on floor• Sealed combustion• Requires condensate drain

Mod/con (e.g., modulating / condensing) boilers are built with the intent that fluid gases will condense within the boiler.

High efficiency gas-fired boilers


atmospheric draft

modulating / condensing boilers, plenty to choose from...

These are all “low mass” mod/con boilers



atmospheric draft

modulating / condensing combi-units (space heat + DHW)

Triangle Tube

hot water

cold water

to / from!space!

heating

internal!circulator

motorized!diverter!valve

stainless steel!brazed plate!

heat exchanger

anti-scald!valve

flow!switch

combi-boiler

LAARS

Designed for “on-demand” DHW. 30-45 seconds from cold start to rated DHW delivery temperature.



atmospheric draft

To prevent short cycling - these boilers are often installed with a buffer tank.


buffer tank

mod/con boiler!(low mass)

to /

from

!he

atin

g lo

adtemperature!sensor

HIGH THERMAL MASS mod/con heating appliancesHigh efficiency gas-fired boilers

• “Self-buffering” heat source. No buffer tank required.

• Low pressure drop - no separate circulator required

HTP, Inc “Pioneer” heating appliance

add on DHW module to create combi-unitHigh efficiency gas-fired boilers

APPLIANCE!for space heating!

and DHW

panel radiator TRV

cold

DHW

European approach to combined space heating & DHW

ACVRotex


Do you notice anything in common among these products?• None of them look like a boiler or water heater...

• They all look like an “appliance.”

• They all have sufficient water volume to stabilize against short cycling the burner under light loading.

This is what some North American systems look like.

European approach to combined space heating & DHW


Solar assisted space heating & DHW, high mass mod/conHigh efficiency gas-fired boilers


atmospheric draft

DESIGN ISSUE: To obtain high efficiency ( 88 to 97%), the water temperature supplied to the mod/con boiler must be lower than the dewpoint of the exhaust gases.

Condensing mode operation begins at inlet water temperatures of about 130 ºF, and corresponding thermal efficiency of about 87.5%.

Thermal efficiency climbs as inlet water temperature decreases.

Inlet water temperature is a function of system design.

Applying mod/con boilers in higher temperature systems is generally not recommended.

LOW WATER TEMPERATURE ARE CRUCIAL TO HIGH PERFORMANCEHigh efficiency gas-fired boilers


atmospheric draft

Many mod/con boilers have compact heat exchangers:

Whatʼs good about this: Very low metal and water content.Whatʼs bad about this: Very low metal and water content.

DESIGN ISSUE: Low thermal mass boilers combined with highly zoned distribution systems will cause “short cycling.”

TYPICAL SOLUTION: add thermal mass in the form of a buffer tank.

heating load

(Btu/hr)

time (hr)

minimum modulation = 20% of full output

20%

100%

heating load profileheating load profile

heat source must cycle on/off to supply loads!under 20% of full output

10%

on at 30%, then stabilizeramp downhold at 20%, then off



atmospheric draft

DESIGN ISSUE: The very low pressure drop associated with cast-iron sectional boilers, and most fire tube boilers allows full system flow to pass through boiler.

0

5

10

15

20

25

0 2 4 6 8 10 12

pres

sure

dro

p (p

si)

flow rate (gpm)

100,000 Btu/hr !compact mod/con

100,000 Btu/hr !cast-iron sectional

VENT

conventional boiler!with low flow resistance



atmospheric draft

DESIGN ISSUE: Compact boiler heat exchangers also create significantly higher pressure drop as fluid flows through them.

0

5

10

15

20

25

0 2 4 6 8 10 12

pres

sure

dro

p (p

si)

flow rate (gpm)

100,000 Btu/hr !compact mod/con

100,000 Btu/hr !cast-iron sectionalTYPICAL SOLUTION: Use a dedicated

boiler circulator to create flow through boiler, in combination with some form of hydraulic separation.

Many compact modulating / condensing boilers create high pressure drop

compactmod/con

heat exchanger

cast-ironsectional boiler



atmospheric draft

closely spaced tees

very low flow resistance!common piping!

high flow ! resistance boiler

size headers for max flow velocity of 2 ft/sec


TYPICAL SOLUTION: Use a dedicated boiler circulator to create flow through boiler, in combination with some form of hydraulic separation.

Hydraulic separation using closely spaced tees.



atmospheric draft

buffer!tank



boiler!circulator

high flow resistance boiler



Hydraulic separation using buffer tank.



atmospheric draft



hydraulic separator


high flow ! resistance boiler


Hydraulic separation using hydraulic separator.


solar

collec

tor ar

rayin

itial

lift

hea

d

thermal!storage!

tank

pressure regulated!variable speed circulator

3-way motorized mixing valve!(provides outdoor reset control)

zoned radiant ceiling panels

manifold valve actuators

variable speed!collector circulator

modulating / condensing

boiler

outdoor!temperature!

sensor

air return tube

air return tubedrainback /!

expansion space

temperature sensor mounted to absorber plate, or well within collector

DHW

Solar combisystem with drainback freeze

protection

Top of tank maintained at

minimum of 120 ºF

Low temperature / low mass hydronic

heat emitters

Low temperature / low mass hydronic heat emitters

2

2.5

3

3.5

4

4.5

5

5.5

6

6.5

-10 0 10 20 30 40 50 60 70CO

POutdoor air temperature (ºF)

leaving load water temp = 86 ºF

leaving load water temp = 104 ºFleaving load water temp = 122 ºF

Heat sources such as condensing boilers, geothermal & ATW heat pumps, and solar collectors all benefit from low water temperature operation.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

60 80 100 120 140 160 180 200

ther

mal

effi

cien

cy (d

ecim

al %

)

inlet fluid temperature (ºF)

ambient air temp. = 30ºF!solar radiation = 250 Btu/hr/ft2)

3.5

3.7

3.9

4.1

4.3

4.5

4.7

4.9

5.1

100 105 110 115 120 125

Coef

ficie

nt O

f Per

form

ance

(CO

P)

Entering water temperature (ºF)

Is radiant floor heating always the answer?

“Barefoot friendly” floors...

Consider a 2,000 square foot well insulated home with a design heat loss of 18,000 Btu/hr. Assume that 90 percent of the floor area in this house is heated (1800 square feet). The required upward heat flux from the floor at design load conditions is:

heat flux= design loadfloor area

= 18,000 Btu/hr1,800 square feet

=10 Btuhr•ft2

To deliver 10 Btu/hr/ft2 the floor only has to exceed the room temperature by 5 degrees F. Thus, for a room at 68 degrees F the average floor surface temperature is only about 73 degrees F. ?This is not going to deliver "barefoot friendly floors" - as so many ads for floor heating promote.

Is radiant floor heating always the answer?

Tf = average floor surface temperature (ºF)Tr= room air temperature (ºF)q=heat flux (Btu/hr/ft2)

Why radiant floor heating ISN'T always the best choice…Direct gain passive solar buildings…

Initial concept: Since the insulated floor slab is already there- why not add tubing to keep it warm on cloudy days?

The passive solar concept relies on the floor mass giving up it’s heat at night.

If maintained at an elevated temperature with auxiliary heat ensuing solar gains cannot be absorbed.

The space quickly overheats.

A comparison of THERMAL MASS for several heat emitters:All heat emitters sized to provide 1000 Btu/hr at 110 ºF average water temperature, and 70 ºF room temperature:

Low thermal mass allows the heat emitters to quickly respond to changing internal loads

Notice where the tubing is in this 6” heated concrete slab

Donʼt do this with ANY hydronic heat source!

Heat transfer between the water and the upper floor surface is severely restricted!

Documents

Best Practices in Modern Hydronic Heating - AN … · "Best Practices in Modern Hydronic Heating ... this cut would destroy the load-carrying ... • None of them look like a boiler